How do alder trees affect nitrogen content in soil

Nitrogen-fixing red alder trees tap rock-derived nutrients

Proc Natl Acad Sci U S A. 2019 Mar 12; 116(11): 5009–5014.

Published online 2019 Feb 25. doi: 10.1073/pnas.1814782116


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Tree species that form symbioses with nitrogen-fixing bacteria can naturally fertilize forests by converting atmospheric nitrogen gas into plant-available forms. However, other mineral nutrients that plants require for growth are largely locked in bedrock, and are released only slowly into soil. We used strontium isotopes to trace nutrient sources for six common tree species in a temperate rainforest, including one species from a globally widespread genus known for high rates of biological nitrogen fixation. We found that trees capable of fixing atmospheric nitrogen gas were also best able to directly access mineral nutrients from bedrock. This gives nitrogen-fixing trees the unique ability to provide the full suite of essential nutrients required to fuel growth and carbon uptake in forest ecosystems.

Keywords: nitrogen fixation, mineral weathering, forest, biogeochemistry, strontium isotopes

Symbiotic nitrogen (N)-fixing trees supply significant N inputs to forest ecosystems, leading to increased soil fertility, forest growth, and carbon storage. Rapid growth and stoichiometric constraints of N fixers also create high demands for rock-derived nutrients such as phosphorus (P), while excess fixed N can generate acidity and accelerate leaching of rock-derived nutrients such as calcium (Ca). This ability of N-fixing trees to accelerate cycles of Ca, P, and other rock-derived nutrients has fostered speculation of a direct link between N fixation and mineral weathering in terrestrial ecosystems. However, field evidence that N-fixing trees have enhanced access to rock-derived nutrients is lacking. Here we use strontium (Sr) isotopes as a tracer of nutrient sources in a mixed-species temperate rainforest to show that N-fixing trees access more rock-derived nutrients than nonfixing trees. The N-fixing tree red alder (Alnus rubra), on average, took up 8 to 18% more rock-derived Sr than five co-occurring nonfixing tree species, including two with high requirements for rock-derived nutrients. The increased access to rock-derived nutrients occurred despite spatial variation in community‐wide Sr sources across the forest, and only N fixers had foliar Sr isotopes that differed significantly from soil exchangeable pools. We calculate that increased uptake of rock-derived nutrients by N-fixing alder requires a 64% increase in weathering supply of nutrients over nonfixing trees. These findings provide direct evidence that an N-fixing tree species can also accelerate nutrient inputs from rock weathering, thus increasing supplies of multiple nutrients that limit carbon uptake and storage in forest ecosystems.

Trees can accelerate mineral weathering in soil and the release of essential nutrients from bedrock into ecosystems. There are many ways that trees promote weathering: by anchoring soils, by altering hydrologic cycling, by secreting organic acids and chelating agents, by reducing pH around root hairs, and by stimulating production of carbonic acid from root respiration and organic matter decomposition (1–3). All essential nutrients that trees require can be provided by mineral weathering, including nitrogen (N) in some geologic settings (4). Typically, however, most N inputs to ecosystems originate from biological fixation and atmospheric deposition (5). Consequently, couplings between plant N nutrition and mineral weathering remain largely speculative (6, 7). Understanding links between plant N nutrition and mineral weathering could contribute to climate, food, fiber, and soil security while minimizing release of excess N to the environment (8).

Nitrogen is the nutrient that most commonly limits tree growth, soil fertility, and carbon (C) storage in forests worldwide (5, 9, 10). Nitrogen limitation occurs due to a combination of low N inputs relative to annual plant demands, and persistent N losses that constrain N accumulation and availability in soil (4–7). Nitrogen input from biological N fixation converts inert atmospheric N2 gas into biologically available N in ecosystems. This evolutionary adaption to low N availability can eliminate N limitation in individual organisms, but less frequently eliminates community-wide N limitation (5, 11). An exception to this can occur in symbioses where woody plants support N-fixing bacteria in root nodules (hereafter “N fixers”). These symbioses can in some cases support exceptionally high rates of N fixation that exceed host plant N requirements, leading to excess N supply and community-wide N sufficiency that shifts nutrient limitation away from N toward other nutrients such as P and Ca (12, 13).

Non-N mineral nutrients such as P and Ca are taken up by plants from soil, yet are supplied ultimately to ecosystems by atmospheric deposition and bedrock weathering (5–7, 12, 14). Atmospheric deposition typically provides most non-N nutrients only sparingly relative to potential inputs from bedrock. As a result, non-N mineral nutrients are often considered “rock-derived,” and their availability depends on internal ecosystem processes that influence weathering inputs. Both plant (1–3) and microbial (15, 16) processes can accelerate mineral weathering in ecosystems, including several pathways that involve combined effects of plants and microbes (15–18). In forests, there is particular interest in whether certain classes of trees or mycorrhizal symbioses can accelerate weathering and uptake of rock-derived nutrients (17, 18). Early syntheses of terrestrial biogeochemistry theorized that symbiotic N-fixing trees may be one class of plant−microbial symbioses that can accelerate mineral weathering to release P and metallic cations for biotic uptake (6, 7). If true, such a role would place N fixers at a nexus of ecosystem nutrient sourcing, with potential for feedbacks between fixed N and rock-derived nutrients that regulate soil fertility, plant growth, and ecosystem C storage.

We used radiogenic Sr isotopes, 87Sr/86Sr (14, 18–20), to identify nutrient sources for six codominant tree species in a temperate rainforest in Oregon. Our prior work in this region established two distinct and well-constrained end-members of potential Sr sources to forests: atmospheric inputs of Sr from the nearby Pacific Ocean and mineral weathering inputs of rock-derived Sr from local basalt (20). These two sources are equally important, on average, in supplying Sr to forest ecosystems across the region (average rock-derived Sr = 48% of total, range = 14 to 90%, SE = 8, n = 11; ref. 20). However, potential differences among dominant tree species in Sr sources within these forests have not been examined. By comparing Sr isotopes in foliage to known end-members, we determined the proportions of atmospheric vs. rock-derived nutrient sources taken up by individual trees in mixed-species plots. We established six replicate study plots across a 15-ha study forest, with each plot containing all six tree species within a <0.1-ha area. The species consisted of one actinorhizal N-fixing angiosperm that also forms symbioses with ectomycorrhizal fungi, one additional nonfixing angiosperm with arbuscular mycorrhizae, three nonfixing gymnosperms with ectomycorrhizae, and one nonfixing gymnosperm with arbuscular mycorrhizae (). The soil has high N levels () typical of the region, and which lead to incipient Ca and P limitation of forest growth (13). Naturally high N availability in these forests shapes nutrient cycles in a manner similar to high inputs of N from anthropogenic deposition (21, 22), and provides context for broader identification of how ecosystem N enrichment alters cycles of rock-derived nutrients.

Table 1.

Tree species characteristics and foliar chemical and isotopic values in a temperate rainforest

PropertyBigleaf mapleRed alderSitka spruceDouglas-firWestern redcedarWestern hemlockPlot P value
Species nameAcer macrophyllumAlnus rubraPicea sitchensisPseudotsuga menziesiiThuja plicataTsuga heterophylla
N fixerNoYesNoNoNoNo
C, %50. 28 a50.26 a51.95 b51.98 b52.45 b52.75 b0.30
N, %3.21 a2.56 b1.41 c1.34 c1.28 c1.28 c0.72
Ca, mg⋅g−19.09 d6.40 b4.05 a7. 83 c10.65 d3.15 a0.29
Sr, µg⋅g−196.33 a103.15 a123.88 a73.70 a83.39 a8.18 b0.45
Mg, mg⋅g−13.19 c3.92 d0.99a1.86 b1.72 b1.09 a0. 33
K, mg⋅g−112.11 a9.13 b8.86 b9.25 b5.49 c6.01 c0.81
P, mg⋅g−13.92 b2.24 a1.99 a2.14 a1.80 a1.84 a0.28
C:N, mass15.69 a19. 68 b36.91 c39.04 d41.50 d41.24 d0.23
N:P, mass8.24 a11.70 b7.44 a6.24 a7.42 a7.00 a0.39
Ca:Sr, mol212.58 a139.25 a81.26 a232.36 a282. 21 a949.69 b0.27
δ15N, ‰−2.24 b−1.14 a−2.07 b−2.29 b−3.22 c−3.24 c0.38
δ13C, ‰−30.34 a−30.54 a−30.68 a−29.80 a−28.44 b−29.74 a0.24
87Sr/86Sr0. 70622 b0.70557 a0.70601 b0.70611 b0.70618 b0.70654 c<0.001
% Rock Sr54.2 b66.3 a58.1 b56.2 b55.0 b48.2 c<0.001
% Rock Ca66.5 b76.7 a70.2 b68. 3 b67.3 b61.1 c<0.001

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Tree species data are means across six mixed-species study plots. Different letters within a row denote significant differences among species, from post hoc Tukey test (P ≤ 0.05). Plot P value is block effect in ANOVA. Deciduous/Evergreen (Decid/Ever) is classified as follows: D, deciduous; E, evergreen. Mycorrhizae are classified as follows: A, arbuscular; E, ectomycorrhizal. Shade tolerance is classified as follows: INTOL, intolerant; TOL, tolerant; VTOL, very tolerant (47). The % rock Sr and Ca are calculated from Eqs. 1 and 2, respectively.

Table 2.

Mineral soil (0 cm to 10 cm) properties across the forest

pH4. 550.11
Total C, %16.502.68
Total N, %0.820.13
Caexch, µg⋅g−1750.3171.3
Mgexch, µg⋅g−1418.6139.2
Kexch, µg⋅g−1225.728.1
Naexch, µg⋅g−162. 316.5
Srexch, µg⋅g−110.02.8
C:N, mass20.21.2
Ca:Sr, molar186.214.5
δ13C, ‰−26.970.2
δ15N, ‰0.790.25
87Sr/86Sratmos0. 709160.00005
% Rock Srexch51.82.4
% Rock Caexch64.52.2

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Values are means and SEs (n = 8) from a transect bisecting the forest. Values of 87Sr/86Sratmos and 87Sr/86Srbedrock are from ref. 20, 87Sr/86Srexch are Sr isotopes in soil exchangeable pool, and % rock Srexch and Caexch are from Eqs. 1 and 2, respectively.

We found that N-fixing red alder trees (species code ALRU) obtained significantly more rock-derived Sr than all five codominant nonfixing trees in this mixed temperate rainforest (ANOVA, P < 0.001). In a two-source mixing calculation comparing atmospheric vs. bedrock Sr contributions (Methods and Eq. 1), N-fixing alder displayed a bedrock source of Sr (average = 66% bedrock-derived Sr, SE = 4%) that averaged 8 to 18% greater than nonfixing tree species (range: 48 to 58%; ). Similar calculations to determine Ca sources using Sr isotopes and end-member Ca/Sr ratios likewise suggest that N-fixing red alder relied 7 to 16% more on rock-derived Ca (average = 77%, SE = 3%) than nonfixing tree species (average = 67%, range: 61 to 70%; ). These Ca source calculations are unaffected by Ca/Sr fractionation during biological uptake (Methods, Eq. 2, and ref. 19). Our measured species differences in Sr and Ca sources likely underestimate true differences, due to lateral litterfall mixing and nutrient recycling among neighboring trees (23). Our findings broaden the current view of how symbiotic N-fixing trees influence ecosystem nutrient inputs, from a focus on increased N supply (5, 9–12), to a recognition that N fixers can also accelerate nutrient inputs from rock weathering.

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Percent rock-derived (A) Sr and (B) Ca in six tree species in a mixed-species temperate rainforest. Values are determined from two end-member mixing calculations that partition atmospheric and rock-derived sources (Sr, Eq. 1; Ca, Eq. 2). Tree species values are means and SEs from six mixed-species plots. Asterisks indicate that rock-derived nutrient sources are significantly greater in ALRU (N-fixing red alder) and significantly lower in TSHE (western hemlock) compared with other tree species (P < 0. 001). Shaded areas span the full range of rock-derived Sr and Ca sources measured in the mineral soil exchangeable pool across the forest. See for species codes.

Spatial variability in bedrock Sr inputs across landscape positions can obscure tree species differences in Sr sources (24). We observed significant spatial variability in Sr sources across the forest (ANOVA, P < 0.001), with average values of rock-derived Sr ranging from 44 to 64% among mixed-species plots. This 20% range in Sr sources due to spatial variability among plots was comparable to the 18% range observed among tree species. Despite these significant sources of variability, most individual tree species displayed Sr source patterns that tracked co-occurring species across the forest (, P < 0.05 for all species except Sitka spruce). This tracking among tree species implies a coherent community-level shift in plant nutrient sources in response to spatial variation in bedrock Sr inputs. As the tree community shifted its Sr sources across the site, however, it maintained consistent rankings of tree species reliance on rock-derived Sr, with N-fixing alder relying most on rock-derived Sr in five of six mixed-species plots, and nonfixing western hemlock (species code TSHE) relying least on rock-derived Sr in all six plots (). These consistent rankings highlight distinct species-level strategies of nutrient acquisition, particularly for N-fixing alder and nonfixing hemlock, that are maintained across spatial variation in forest Sr sources.

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Percent rock-derived Sr and Sr isotope values for individual trees (A) regressed against the mean % rock-derived Sr of all other species in each plot and (B) compared among species in each plot. In A, solid lines show linear regressions for ACMA, ALRU, PSME, THPL, and TSHE (all P < 0.05), indicating coherent tracking in Sr sources across the forest. In B, lines connect species across mixed-species plots, and the average of all six species is shown, as are individual mineral soil exchangeable Sr isotope values (n = 8) from a transect across the site.

Comparison of Sr isotopes in plants and soil exchangeable pools further reveals a distinct strategy of nutrient acquisition in N-fixing red alder that is targeted to uptake of rock-derived nutrients. The largest immediate source of “plant available” base cation nutrients in forests typically occurs in the soil exchangeable pool, a loosely held reservoir where nutrients are recycled before plant uptake (25). In the forests studied here, the soil exchangeable pool of Sr is well mixed and biologically available, displays negligible Sr isotope variation with depth, and covaries closely with foliar Sr isotopes across a wide range of site conditions and soil fertility (slope = 1.03, r2 = 0.97, n = 22; ref. 20). Similarly, all species of nonfixers that we examined exhibited considerable overlap of foliage with soil exchangeable Sr isotope values (). This overlap is typical in forests and highlights the important role of nutrient recycling within ecosystems in supplying nutrients to trees (5–7, 18). In contrast, N-fixing red alder was the only tree species whose foliage differed significantly from soil exchangeable Sr isotope values (; ANOVA, P < 0. 05). Red alder foliage was instead biased toward the signature of mineral weathering, implying direct uptake of rock-derived nutrients. This diminished dependence on soil exchangeable Sr, in combination with red alder’s distinct foliar Sr isotope values compared with other species, provides field evidence that N fixers can directly access rock-derived nutrients. By both fixing atmospheric N and taking up nutrients directly from mineral weathering, N fixers may therefore short-circuit the usual reliance of trees on internally recycled nutrients in forests.

The most likely mechanism for a stronger signal of rock-derived Sr in N-fixing alder is increased mineral weathering in the rooting zone caused by nitric acid. Acids often enhance mineral weathering and mobilize rock-derived nutrients in soil (1–3, 26), but may or may not alter soil pH depending on the acid buffering status (27). The generation of nitric acid in soil under red alder results from very high rates of N fixation relative to demands (28–30). This leads to excess soil N as ammonium that is oxidized by soil microorganisms during nitrification to nitrate and acidic protons (i.e., nitric acid). Excess N from biological fixation, atmospheric deposition, and agricultural fertilization can all produce nitric acid. Nitric acid is a strong acid compared with carbonic and organic acid weathering agents (1–3, 15–17, 29), and is very effective at mobilizing exchangeable soil cations (e.g., Sr and Ca) and stimulating coupled cation and nitrate leaching (20–22, 29, 30), as well as enhancing mineral dissolution (31). However, without isotopic tracers, it can be difficult to resolve whether acids mobilize cations from the soil exchangeable pool vs. stimulate mineral weathering (18, 29–33). Our Sr isotope evidence that N-fixing alder directly accesses rock-derived nutrients implicates enhanced mineral weathering in the rooting zone of trees. The mineral weathering likely occurs on minerals mixed throughout soil rather than unweathered bedrock at depth, because rooting depths are consistently shallow (<1 m deep; refs. 34–36) compared with the depth of fresh competent bedrock (>8 m; ref. 20).

Other possible causes of greater uptake of rock-derived Sr in N-fixing alder have less support. We excluded the possibility that N fixers occupied areas with intrinsically high rock-derived Sr by sampling mixed plots containing all focal tree species across a heterogeneous forest (). Mineral soil rooting depths of our study species are generally shallow (<1 m) and overlapping (34–36), and occupy a zone where soil exchangeable Sr isotopes display negligible depth variation (20). Ectomycorrhizal fungi can enhance mineral weathering in some tree species (16–18), but this effect is equivocal in alder (37). Furthermore, ectomycorrhizae were not unique to alder, as four of the six tree species studied support ectomycorrhizae, including western hemlock that relied more on atmospheric Sr (). The divergence in Sr sources between western hemlock and red alder is notable because both species produce highly acidic organic matter (35) that could promote weathering. Western hemlock’s weaker signal of weatherable Sr may reflect some uptake of atmospheric Sr from surface organic soil (36) as well as low weathering rates in mineral soil due to a lack of nitric acid generation (38). Finally, we are unaware of evidence that N-fixing trees directly exude more organic acids for mineral weathering compared with nonfixers, although such a mechanism could complement nitric acid weathering. We note, however, that exudate production from live N-fixing trees would be only transient compared with long-term legacies of soil N saturation that sustain excess nitrification and nitric acid generation across this landscape (20−22).

Our findings shed light on how N-fixing alder accelerates mineral weathering in the rooting zone to increase nutrient supply in our forests. By coupling Sr isotope data of foliage, bedrock, and atmospheric deposition to rates of atmospheric Sr input in mass balance calculations (Methods and Eq. 3), we find that N-fixing alder accelerates mineral weathering input of nutrients by 64% compared with nonfixing trees. This input flux is limited only to the rooting zone of soil, whereas larger-scale weathering fluxes that supply stream export are not addressed in our study. The substantial increase in mineral weathering by N-fixing alder helps explain how this species takes up 65% more P and 200% more Ca than nonfixing Douglas-fir (9). Enhanced access to P is most likely important to N fixers (5, 12), and is used to increase photosynthetic tissue mass and N-fixing nodule production to support growth (39). Strontium is only an indirect tracer of P (14, 40), but can directly trace Ca (14, 18–21). Ecosystem supplies of both P and Ca can limit nonfixer tree growth where N is abundant (12, 41), including in our forests (13). Alder-enhanced uptake of rock-derived Ca and its subsequent redistribution via litterfall may especially benefit bigleaf maple and western redcedar, two nonfixers with consistently high Ca demands (42) that have limited direct access to rock-derived nutrients.

Over long-term soil development, high rates of mineral weathering and solute mobilization can accelerate the pace at which forest ecosystems move through soil process domains. Work along climate gradients has elucidated clear thresholds of soil chemical change, wherein rainfall amount defines distinct domains of relatively stable soil properties (27, 43). Forest soils across our region display a similar nonlinear threshold of base cation depletion as a function of soil N, spanning a well-buffered domain of base-rich soil under low N conditions that changes sharply in N-rich sites to an acidified and poorly buffered domain depleted of weatherable base cations (20, 21). These changes due to soil N are caused ultimately by long-term N inputs from red alder. This N-fixing tree belongs to a widespread genus (Alnus spp) that spans boreal, temperate, and montane tropical regions, and consistently hosts symbiotic bacteria that carry out biological N fixation (44). High soil N in the region that we studied is maintained over millennia by wildfire disturbances that permit alder colonization and N fixation, even when N is not a limiting nutrient (28, 45). The result is sustained soil N saturation that continues to acidify soil and leach base cations even when N-fixing alder is no longer present (22), eventually leading to irreversible depletion of parent rock Ca from soil (20). Such long-term shifts in soil process domains due to excess N further implicate nitric acid generation as a key driver of enhanced mineral weathering in the rooting zone. Where persistent and irreversible depletion of rock-derived nutrients occurs, forests must shift to depend on atmospheric nutrient inputs to sustain primary productivity (14, 20).

Our finding that an N-fixing tree species can directly access rock-derived nutrients has implications for nutrient supplies that regulate tree growth and C uptake in forests. Inputs of fixed N can increase tree growth in N-limited forests (9–11), and could be further stimulated by access to rock-derived nutrients (5, 12, 28, 39). Where N is already abundant and other nutrients are limiting, supplies of rock-derived nutrients can be even more important to forest growth and C uptake (5, 12–14, 41). It is presently unknown whether high rates of N fixation by trees are geographically widespread (10–12), and whether N fixers other than red alder can similarly access rock-derived nutrients. Our suggestion that excess N fixation and nitric acid production can release rock-derived nutrients in forests is analogous to high rates of N fertilization that cause nitric acid-driven weathering in agricultural systems (31, 32). Resolving these interactions more broadly in forests requires new understanding to distinguish N fixers like red alder that routinely fix excess N, from species that down-regulate N fixation when soil N is abundant (11).

Field Site and Sample Collection.

We studied a mixed-species temperate rainforest in the Tillamook State Forest of the north central Oregon Coast Range (45°38′38.46″N, 123°47′51.51″W). The climate has cool wet winters and warm dry summers, with mean annual temperature of 9.4 °C and mean annual precipitation of 352 cm (46). The site is in the low-elevation Sitka spruce forest zone, which is among the most productive forest types worldwide, with exceptionally high plant and soil C storage potential (47). Soils developed from the Tillamook formation of basalt bedrock and are classified as Typic Fulvudands. The soils have high concentrations of total N and low exchangeable Ca (), which is typical of the broader study area (9, 13, 20–22) reflecting long-term legacies of N fixation (45).

We sampled a forest ∼80 y of age, in which trees established naturally after stand-replacing wildfire in 1933. Inspection of the field site and records from the Oregon Department of Forestry indicate that the site has been undisturbed since establishment. The forest has a closed canopy structure and well-integrated mixture of six tree species that codominate in the region. This codominance reflects a diverse availability of seed sources after disturbance, although differences in shade tolerance and longevity will filter species through succession (47). The species we examined include the evergreen conifers Sitka spruce (Picea sitchensis), Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and western redcedar (Thuja plicata) and the deciduous broadleaf trees bigleaf maple (Acer macrophyllum) and symbiotic N-fixing red alder (Alnus rubra).

We established six replicate study plots spanning midslope to upslope across a 15-ha area. Each plot contained a mixture of all six codominant tree species within a 0.1-ha area. We sampled sun foliage using a shotgun from three positions around the canopy of each tree, and composited these into one sample per species per plot. We sampled surface mineral soil (0 cm to 10 cm) using a 6.8-cm-diameter corer in eight locations on a transect bisecting the site.

Sample Processing and Analysis.

Field moist soil pH was determined in a 2:1 mixture of soil and deionized water after 30 min equilibration. Field moist soil was extracted for exchangeable Ca, Sr, Mg, K, and Na using 5 g of soil shaken for 30 min with 25 mL of unbuffered 1M NH4OAc, then filtered through a 0.45-µm Aerodisk PES membrane. Soil moisture was determined by drying at 105 °C for 48 h. Subsamples of foliage and soil were dried at 65 °C for 48 h and ground to fine powder using an agate ball mill before analysis.

Foliage and soil were analyzed for total C and N on a Costech ECS-4010 combustion analyzer at the USGS Forest and Rangeland Ecosystem Science Center, and, for δ13C and δ15N, on a PDZ Europa 20-20 isotope ratio mass spectrometer at the University of California, Davis Stable Isotope Facility. Foliage Ca, Sr, Mg, K, and P was processed with nitric acid microwave digestion. Foliage digests and soil exchangeable nutrients were analyzed using inductively coupled plasma optical emission spectrometry at the W. M. Keck Collaboratory at Oregon State University. Based on repeat analyses of standard reference materials, uncertainty for C was 1.5%, for N was 2.7%, for δ13C was 0.2‰, for δ15N was 0.3‰, and for Ca, Sr, Mg, K, and P was less than 5%.

Strontium isotopes (87Sr/86Sr) in foliage and soil exchangeable fractions were determined by purifying 30 ng of Sr using 1.8 mL of Eichrom AG50W-X8 (H+ form) cation resin followed by 50 µL of Eichrom Sr-Spec resin. Isotopic measurements were made on a Nu Plasma multicollector inductively coupled plasma mass spectrometer at the W. M. Keck Collaboratory at Oregon State University. Masses 83 to 88 were monitored in static collection mode. Masses 83 and 85 were monitored for Kr (blank only) and Rb (standards and samples) interferences. Sr isotope ratios were measured 40 times per sample and have analytical uncertainties of <0.000020. Reported values are corrected to 86Sr/88Sr = 0.1194 and Sr standard NBS-987 87Sr/86Sr = 0.710245. This instrument measured an average value of 0.70818 and a 2σ = 0.000045 for an in-house standard (EMD Millipore) (n = 205) over the duration that samples were run.

Strontium Isotope Mixing Calculations.

An extensive study of 22 forests across the region found, previously, that ecosystem inputs of Sr and Ca were dominated by two distinct sources: atmospheric inputs from sea salt aerosols in rainwater and mineral weathering inputs from bedrock (20). That study measured end-member values of atmospheric inputs for 87Sr/86Sr of 0.70916 and Ca/Sr(molar) of 138.87, and of mineral weathering of Tillamook Formation basalt from 1 M HNO3 leaches of fresh bedrock for 87Sr/86Sr of 0.70374 and Ca/Sr(molar) of 236.30 (20). This well-constrained, two-component system permits the use of standard equations to partition Sr and Ca in foliage and soil exchangeable pools into contributions from atmospheric versus rock-derived sources (19). We calculated the fractional contribution of rock-derived Sr to foliage and soil exchangeable pools using



where (87Sr/86Sr)mix is the Sr isotope ratio of foliage or soil exchangeable pools, (87Sr/86Sr)rock is the Sr isotope ratio of 1 M HNO3 bedrock leachate, and (87Sr/86Sr)atm is the Sr isotope ratio of rainfall. Our primary inferences regarding tree species access to rock-derived nutrients rely on Eq. 1. Tracing Ca dynamics with Sr isotopes requires modification of Eq. 1 to include molar Sr/Ca ratios of end-members (19), yielding the mass fraction of rock-derived Ca in foliage or soil exchangeable pools, as in



This calculation of % rock-derived Ca uses Sr/Ca ratios of atmospheric deposition and weathering, but does not use Sr/Ca ratios of the mixture (i.e., foliage or soil exchangeable pool). This calculation is therefore unaffected by biological processes that discriminate between Ca and Sr (19). Biological processes do not discriminate appreciably between 87Sr and 86Sr, and what little fractionation may occur is corrected during the mass spectrometer bias correction. Substitution of 87Sr/86Sr and Sr/Ca values from whole-rock digests instead of nitric acid leaches of bedrock in Eqs. 1 and 2 yields roughly 2% more rock-derived Sr and Ca, with no change in patterns among species.

We calculated weathering rates under N-fixing and nonfixing species using



where Inputatm is the Sr flux of atmospheric inputs, estimated at 0.33 mol⋅ha−1⋅y−1 Sr based on 350 cm⋅y−1 mean annual precipitation and measured precipitation chemistry (20, 46, 48). The average 87Sr/86Sr of atmospheric inputs is 0.70916 (SE = 0.00005, n = 3; compare with seawater = 0.70917), and the average 87Sr/86Sr of 1 M HNO3 leachates of fresh Tillamook formation rocks is 0.70374 (SE = 0.00007, n = 5) (20). This yields an average weathering rate for our five nonfixing species of 0.397 mol Sr⋅ha−1⋅y−1 and, for N-fixing red alder, of 0.650 mol Sr⋅ha−1⋅y−1, leading to 64% higher weathering rates under alder. These Sr isotope-based weathering rates represent the input of Sr from basalt minerals to the biologically cycled pool of Sr, consisting of soil exchangeable cations in the rooting zone plus plant biomass. This calculated weathering flux represents a supply from weathering to the trees, and is limited to the rooting zone ∼1 m deep at our site. Consequently, this rooting zone weathering input flux is not directly comparable to a landscape-scale weathering output flux. Sr isotopes do not fractionate during weathering, and, in basalt, ions such as Sr2+, Ca2+, and HCO3 are released congruently with the dissolution of major phases such as olivine, plagioclase, pyroxene, and volcanic glass. The differences in both 87Sr/86Sr signatures and weathering rates among major mineral phases in basalt are negligible in the context of the range of values observed in most ecosystem studies (19). This well‐constrained behavior of Sr isotopes during basalt weathering permits insights not possible in more heterogeneous types of bedrock.

Statistical Analyses.

We tested for differences among tree species in foliar chemistry, isotopes, and % rock-derived Sr and Ca using ANOVA blocked by plot, with Tukey B post hoc comparisons. Community-level tracking in % rock-derived Sr among tree species was evaluated using least-squares linear regression. Significance was set at P ≤ 0.05. Analyses were performed using SYSTAT v13.

We thank April Strid, Kecia Jones, Haley Casebier, Chris Catricala, Valerie Maule, George Pope, Collin Ruark, and Brian Haley for field and laboratory assistance; Stephen Porder and Jana Compton for manuscript comments; and the Oregon Department of Forestry for site access. Support was provided by National Science Foundation Grants DEB-1457650 (to S.S.P.) and EAR-1053470 (to J.C.P.-R.). Any use of trade names does not imply endorsement by the US government.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

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1. Kelly EF, Chadwick OA, Hilinski TE. The effect of plants on mineral weathering. Biogeochemistry. 1998;42:21–53. [Google Scholar]

2. Moulton KL, West J, Berner RA. Solute flux and mineral mass balance approaches to the quantification of plant effects on silicate weathering. Am J Sci. 2000;300:539–570. [Google Scholar]

3. Pawlik Ł, Phillips JD, Šamonil P. Roots, rock, and regolith: Biomechanical and biochemical weathering by trees and its impact on hillslopes—A critical literature review. Earth Sci Rev. 2016;159:142–159. [Google Scholar]

4. Houlton BZ, Morford SL, Dahlgren RA. Convergent evidence for widespread rock nitrogen sources in Earth’s surface environment. Science. 2018;360:58–62. [PubMed] [Google Scholar]

5. Vitousek PM, Howarth RW. Nitrogen limitation on land and in the sea: How can it occur? Biogeochemistry. 1991;13:87–115. [Google Scholar]

6. Gorham E, Vitousek PM, Reiners WA. The regulation of chemical budgets over the course of terrestrial ecosystem succession. Annu Rev Ecol Syst. 1979;10:53–84. [Google Scholar]

7. Reiners WA. Nitrogen cycling in relation to ecosystem succession. In: Clark FE, Roswall T, editors. Terrestrial Nitrogen Cycles: Processes, Ecosystem Strategies, and Management Impacts. Ecol Bull; Stockholm: 1981. pp. 507–528. [Google Scholar]

8. Beerling DJ, et al. Farming with crops and rocks to address global climate, food and soil security. Nat Plants. 2018;4:138–147. [PubMed] [Google Scholar]

9. Binkley D, Sollins P, Bell R, Sachs D, Myrold D. Biogeochemistry of adjacent conifer and alder‐conifer stands. Ecology. 1992;73:2022–2033. [Google Scholar]

10. Wieder WR, Cleveland CC, Lawrence DM, Bonan GB. Effects of model structural uncertainty on carbon cycle projections: Biological nitrogen fixation as a case study. Environ Res Lett. 2015;10:044016. [Google Scholar]

11. Menge DN, Levin SA, Hedin LO. Facultative versus obligate nitrogen fixation strategies and their ecosystem consequences. Am Nat. 2009;174:465–477. [PubMed] [Google Scholar]

12. Vitousek PM, Porder S, Houlton BZ, Chadwick OA. Terrestrial phosphorus limitation: Mechanisms, implications, and nitrogen-phosphorus interactions. Ecol Appl. 2010;20:5–15. [PubMed] [Google Scholar]

13. Mainwaring DB, Maguire DA, Perakis SS. Three-year growth response of young Douglas-fir to nitrogen, calcium, phosphorus, and blended fertilizers in Oregon and Washington. For Ecol Manage. 2014;327:178–188. [Google Scholar]

14. Chadwick OA, Derry LA, Vitousek PM, Huebert BJ, Hedin LO. Changing sources of nutrients during four million years of ecosystem development. Nature. 1999;397:491–497. [Google Scholar]

15. Uroz S, Calvaruso C, Turpault MP, Frey-Klett P. Mineral weathering by bacteria: Ecology, actors and mechanisms. Trends Microbiol. 2009;17:378–387. [PubMed] [Google Scholar]

16. Hoffland E, et al. The role of fungi in weathering. Front Ecol Environ. 2004;5:258–264. [Google Scholar]

17. Quirk J, et al. Evolution of trees and mycorrhizal fungi intensifies silicate mineral weathering. Biol Lett. 2012;8:1006–1011. [PMC free article] [PubMed] [Google Scholar]

18. Blum JD, et al. Mycorrhizal weathering of apatite as an important calcium source in base-poor forest ecosystems. Nature. 2002;417:729–731. [PubMed] [Google Scholar]

19. Capo RC, Stewart BW, Chadwick OA. Strontium isotopes as tracers of ecosystem processes: Theory and methods. Geoderma. 1998;82:197–225. [Google Scholar]

20. Hynicka JD, Pett-Ridge JC, Perakis SS. Nitrogen enrichment regulates calcium sources in forests. Glob Change Biol. 2016;22:4067–4079. [PubMed] [Google Scholar]

21. Perakis SS, et al. Coupled nitrogen and calcium cycles in forests of the Oregon Coast Range. Ecosystems. 2006;9:63–74. [Google Scholar]

22. Perakis SS, Sinkhorn ER. Biogeochemistry of a temperate forest nitrogen gradient. Ecology. 2011;92:1481–1491. [PubMed] [Google Scholar]

23. Waring BG, et al. Pervasive and strong effects of plants on soil chemistry: A meta-analysis of individual plant ‘Zinke’ effects. Proc Biol Sci. 2015;282:20151001. [PMC free article] [PubMed] [Google Scholar]

24. Meek K, Derry L, Sparks J, Cathles L. 87Sr/86Sr, Ca/Sr, and Ge/Si ratios as tracers of solute sources and biogeochemical cycling at a temperate forested shale catchment, central Pennsylvania, USA. Chem Geol. 2016;445:84–102. [Google Scholar]

25. Bormann FH, Likens GE. Nutrient cycling. Science. 1967;155:424–429. [PubMed] [Google Scholar]

26. Hartmann J, et al. Enhanced chemical weathering as a geoengineering strategy to reduce atmospheric carbon dioxide, supply nutrients, and mitigate ocean acidification. Rev Geophys. 2013;51:113–149. [Google Scholar]

27. Vitousek PM, Chadwick OA. Pedogenic thresholds and soil process domains in basalt-derived soils. Ecosystems. 2013;16:1379–1395. [Google Scholar]

28. Binkley D, Cromack K, Jr, Baker DD. Nitrogen fixation by red alder: Biology, rates, and controls. In: Hibbs DE, DeBell DS, Tarrant RF, editors. The Biology and Management of Red Alder. Oregon State Univ Press; Corvallis, OR: 1994. pp. 57–72. [Google Scholar]

29. Homann PS, Van Miegroet H, Cole DW, Wolfe GV. Cation distribution, cycling, and removal from mineral soil in Douglas-fir and red alder forests. Biogeochemistry. 1992;16:121–150. [Google Scholar]

30. Compton JE, Church MR, Larned ST, Hogsett WE. Nitrogen export from forested watersheds in the Oregon Coast Range: The role of N2-fixing red alder. Ecosystems. 2003;6:773–785. [Google Scholar]

31. Pierson-Wickmann AC, et al. High chemical weathering rates in first-order granitic catchments induced by agricultural stress. Chem Geol. 2009;265:369–380. [Google Scholar]

32. Perrin AS, Probst A, Probst JL. Impact of nitrogenous fertilizers on carbonate dissolution in small agricultural catchments: Implications for weathering CO2 uptake at regional and global scales. Geochim Cosmochim Acta. 2008;72:3105–3123. [Google Scholar]

33. Watmough SA, et al. Sulphate, nitrogen and base cation budgets at 21 forested catchments in Canada, the United States and Europe. Environ Monit Assess. 2005;109:1–36. [PubMed] [Google Scholar]

34. Smith JHG. Root spread can be estimated from crown width of Douglas fir, lodgepole pine, and other British Columbia tree species. For Chron. 1964;40:456–473. [Google Scholar]

35. Burns RM, Honkala BH. 1990. Silvics of North America. Agriculture Handbook (USDA Forest Serv, Washington, DC), Vol 654.

36. Eis S. Root system morphology of western hemlock, western red cedar, and Douglas-fir. Can J Res. 1974;4:28–38. [Google Scholar]

37. Yamanaka T, Li CY, Bormann BT, Okabe H. Tripartite associations in an alder: Effects of Frankia and Alpova diplophloeus on the growth, nitrogen fixation and mineral acquisition of Alnus tenuifolia. Plant Soil. 2003;254:179–186. [Google Scholar]

38. Turner DP, Franz EH. The influence of western hemlock and western redcedar on microbial numbers, nitrogen, and nitrification. Plant Soil. 1985;88:259–267. [Google Scholar]

39. Uliassi DD, Ruess RW. Limitations to symbiotic nitrogen fixation in primary succession on the Tanana River floodplain. Ecology. 2002;83:88–103. [Google Scholar]

40. Pett-Ridge JC. Contributions of dust to phosphorus cycling in tropical forests of the Luquillo Mountains, Puerto Rico. Biogeochemistry. 2009;94:63–80. [Google Scholar]

41. Vadeboncoeur MA. Meta-analysis of fertilization experiments indicates multiple limiting nutrients in northeastern deciduous forests. Can J Res. 2010;40:1766–1780. [Google Scholar]

42. Cross A, Perakis SS. Tree species and soil nutrient profiles in old-growth forests of the Oregon Coast Range. Can J Res. 2010;41:195–210. [Google Scholar]

43. Dixon JL, Chadwick OA, Vitousek PM. Climate‐driven thresholds for chemical weathering in postglacial soils of New Zealand. J Geophys Res Earth Surf. 2016;121:1619–1634. [Google Scholar]

44. Põlme S, Bahram M, Kõljalg U, Tedersoo L. Global biogeography of Alnus-associated Frankia actinobacteria. New Phytol. 2014;204:979–988. [PubMed] [Google Scholar]

45. Perakis SS, Sinkhorn ER, Compton JE. δ15N constraints on long-term nitrogen balances in temperate forests. Oecologia. 2011;167:793–807. [PubMed] [Google Scholar]

46. Wang T, Hamann A, Spittlehouse D, Carroll C. Locally downscaled and spatially customizable climate data for historical and future periods for North America. PLoS One. 2016;11:e0156720. [PMC free article] [PubMed] [Google Scholar]

47. Franklin JF, Dyrness CT. Natural Vegetation of Oregon and Washington. Oregon State Univ Press; Corvallis, OR: 1988. [Google Scholar]

48. National Atmospheric Deposition Program 2014 National Atmospheric Deposition Program (NRSP-3). Available at Accessed June 27, 2013.

A Weed, or Just the Tree We Need?

Each spring the serrated leaves of the red alder grow anew and each autumn they fall to the forest floor and into nearby streams bringing nutrients with them. (Garrett Dalan)

Coastal Forests Could Increase Resilience, Carbon Sequestration by Planting Red Alder

By Garrett Dalan, Community Relations Manager, The Nature Conservancy, [email protected]

In the Northwest coastal forests where the landscape is dominated by Douglas fir and similar conifers, it may be time to incorporate a greater proportion of red alder. In the struggle with the impacts from climate change, red alder could provide a path to greater resilience and increased near-term carbon sequestration, while continuing to provide economic opportunities.

This would be achieved by taking advantage of a few key characteristics, including fast early growth and shorter total lifespan; the ability to thrive in areas where conifers may not, the benefit to many bird species, insects and pollinators; nitrogen fixing and improvement of soils’ mineral content, especially after major disturbance such as wildfire; and a high moisture content making it potentially less conducive to wildfire spread.

Rapid growth makes red alder an efficient carbon sequestration engine at an early age. Based on studies published by the U.S. Forest Service (Berntsen, 1961) one can infer that if planted today, young alder stands in some sites can remove nearly twice as much CO2 from the atmosphere than conifers during their first 30 years. Although conifers eventually surpass red alder’s total, accumulated biomass and substantially outperform it in carbon sequestration over the long term, red alder may be a viable tool for meeting crucial short-term targets in the next 30 years of climate mitigation efforts.

The mottled, ashy-gray bark of the red alder can help it stand out a Northwest forest, but it is the unseen nitrogen-fixing nodules on its roots that makes it stand out ecologically (Garrett Dalan).

On a board-foot basis, red alder’s economic value can exceed that of most conifers, aside from cedar (Gedney, 1990). In its first 20 years, red alder accumulates biomass twice as fast as conifers (Berntsen, 1961), while its height can increase two and a half times faster than conifers (Deal and Harrington, 2006). By contrast, most conifers, including Douglas Fir and Hemlock, have slow growth rates the first 15 years, followed by rapid growth rates starting around their 20th year (Berntsen, 1961; Deal and Harrington, 2006). Red alder’s rapid early growth means final harvest can occur as early as 30 years after planting, a shorter harvest rotation than typical conifers. An easy to work hardwood, red alder can mimic more expensive woods, making it an excellent furniture choice.

Ecologically, alder increases soil productivity by fixing nitrogen in the soil and adding soil organic matter. It is the only commercial, nitrogen-fixing tree in the Northwest that benefits itself and the surrounding plant life. The leaf detritus fertilizes the forest floor, provides cover for insects and amphibians, and supports aquatic food chains.

Research is being developed as a collaboration between the University of Washington, Oregon State University, The Nature Conservancy and a working group of volunteers along the Washington Coast.

This work will strive towards answering critical questions:

  • Can planting and growing pure red alder stands rather than conifers help in meeting 2050 climate change mitigation targets for Washington State?  Can red alder sequester more carbon (per acre) in a 25-30 year period than a typical Western Washington conifer, such as Douglas-fir or western hemlock?
  • What are the best available tools for estimating growth and yield? How can we use these to characterize alder and conifer productivity across the landscape (driven by soils, topography, climate)?
  • Beyond year 2050, could the occurrence of red alder stands create more carbon sequestration potential by improving later conifer growth through nitrogen fixation and soil amending?
  • Can mixed red alder-conifer plantations capture the benefits of both rapid, early red alder growth and later conifer growth, especially if later conifer growth is enhanced by improved soil conditions?
  • Is red alder less affected by wildfire than conifers? Does red alder interact with wildfire in a different, beneficial way when compared to conifers?
  • Considering red alder’s slow growth after age 30-40 years and relatively short life span, how would harvest of red alder in 30-40 year rotations affect carbon sequestration potential?

This work is expected to occur over the next couple of years with some early findings being available around the end of 2022.   In the meantime, give a strong thought to keeping a few more alder during your next pre-commercial thinning or including alders in your replanting plan.

What was once considered a weed may end up being just what we need.

This is an updated and truncated version of an article written by Dick Binns (Working Group Volunteer), Dr. Indroneil Ganguly (University of Washington), Mike Maki (The Schultes Center) and Garrett Dalan (The Nature Conservancy).


Berntsen, C. 1961. Growth and development of red alder compared with conifers in 30-year-old stands. USDA For. Serv., Res. Pap. PNW-38.

Deal, R.L. and C.A. Harrington, eds. 2006. Red alder—a state of knowledge. General Technical Report PNW-GTR-669. Portland, OR: U.S. Department of Agriculture, Pacific Northwest Research Station. 150 p.

Gedney, Donald R. 1990. Red alder harvesting opportunities. Resour. Bull. PNW-RB-173. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 17 p

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Influence of increased natural growth background on soil enzymatic activity and photosynthesis in shrub alder (Duscheciafruticosa)

I. ManakovKN. Productivity and biological cycle in tundra biogeocenoses of the Kola Peninsula. - JI.: Nauka, 1970. - 159 p.

12. Vikhireva-Vash'kova VV, Gavrilyuk VA, Shamurin VF Overground and underground mass of some shrub communities of the Koryak Land // Problems of the North.-M.; L.: Nauka, 1964,-Issue. 8.-S. 130-147.

13. Ignatenko I.V., Norin B.N., Rakhmanina A.T. Circulation of ash elements and nitrogen in some biogeocenoses of the East European forest tundra // Soils and vegetation of permafrost regions of the USSR. - Magadan: DVNTs AN SSSR, 1973. - S. 335-350.

14. Gasheva A.F. Phytomass reserves of some communities of the station "Kharp" // Biomass and dynamics of vegetation cover and animal population in the forest tundra. - Sverdlovsk, 1974. - S. 106-107.

15. Andreev VN et al. Seasonal and annual dynamics of phytomass in the subarctic tundra. - Novosibirsk: Nauka, 1978.- 191 p.

16. Karpov N.S. Influence of reindeer grazing

on the pasture vegetation of the subarctic tundras of Yakutia.-Yakutsk, 1991.- 116 p.

17. Chepurko N.L. Structure and annual balance of biomass in the forests of the Khibiny massif // Soils and productivity of plant communities. - Issue. 1. -M.: Publishing House of Moscow State University, 1972. - S. 94-116.

18. Levina VI Determination of the mass of annual litter in two types of pine forest on the Kola Peninsula // Bot. magazine - 1960. - T. 45. - No. 3. - S. 418-423.

19. Andreev V.N. Growth of fodder lichens and methods of its regulation // Geobotany: Tr. Institute im. V.L. Komarov Academy of Sciences of the USSR.-M.; L., 1954.-S. 11-74.

20. Andreyashkina N.I. On the methodology for determining annual growth, litter and decay rate in communities of hypoarctic shrubs and shrubs // Botanical journal. - 1987. - T. 72. - No. 4. - S. 1985.

21. Andreyashkina N.I., Peshkova N.V. Comparative analysis of the response of the main phytocenoses of the typical tundra subzone (Yamal Peninsula) to transport impacts // Bot. magazine - 1997. - T. 82. - No. 2. - S. 97-102.

UDC [631.427+(581.132:582.632.1)] (571.56)

Influence of increased natural background of growth on the enzymatic activity of soils and photosynthesis in shrub alder (OcIecia/gnisociaa)

M.M. Shashurin, M.V. Shchelchkova, A.N. Zhuravskaya, V.I. Popov

A study was made of the enzymatic activity of soils and some indicators of photosynthesis of shrub alder leaves under the influence of excessive natural radiation background. It has been established that as the content of uranium in the soil increases, its amount in the leaves of plants increases. It was revealed that the activity of soil enzymes (invertase, urease, catalase and polyphenol oxidase) decreases with an increased γ-background. Also, there is an intensification of photosynthesis and activation of the enzyme ribulose-1,5-diphosphate carboxylase in plant leaves. With an increase in the γ-background of growth (from 20 to 1000 μR/h), the content of low-molecular antioxidants and chlorophyll in alder leaves does not change statistically significantly.

Research offermentation activity of bedrocks and some photosynthesis parameters ofDuschecia fruticosa is carried out at the influence, the exceeded natural radioactive background. Cleared up, that in process of augmentation of uranium contents in bedrock, its amount in leaves increases. It is revealed that at increased r-background activity of edaphic enzymes (invertase, urease, catalase and polyphenol oxidase) decreases. Also there is an intensification of a photosynthesis and activization of an enzyme ribose- 1,5-diphosphate carboxylase in leaves of plants. With augmentation a background ofgrowth (from 20 up to 1000 microentgenfh) the contents of low-molecular antioxidants and chlorophyll in leaves of an alder statistically authentically does not variate.

Modern environmental and biochemical studies of the effect of increased natural radiation background (PERF) on ecosystems in the main

SHASHURIN Mikhail Mikhailovich, post-graduate student of the IPC SB RAS; SHCHELCHKOVA Marina Vladimirovna, Associate Professor of the Department of General Biology, BGF YSU, Ph. D.; ZHURAVSKAYA Alla Nikolaevna group of radiobiology, IPC SB RAS, Doctor of Biological Sciences; POPOV Vyacheslav Ivanovich lab. elemental mass spectrometric analysis AN RS(Y)

nom aimed at studying changes in the physiological and biochemical characteristics of plant and animal organisms [1, 2, 3]. At the same time, the study of the soil component (including its enzymological component), the relationship between the distribution of radionuclides in the "soil - plant" system and the biochemical responses of soil and plant biota, as a rule, is not carried out. At the same time, only a comprehensive radioecological and radiobiological study of

system "soil - plant" in the conditions of PERF allows you to identify patterns of influence of radiation background and toxic radionuclides on the biological parameters of soils (for example, their enzymatic activity) and plants (for example, the process of photosynthesis). Accordingly, the purpose of this work is to reveal the effect of increased natural radiation background in soils and plant tissues on the enzymatic activity of soils and a number of indicators of the photosynthesis process in shrub alder.

Material and methods. The studies were carried out on technogenically disturbed areas of the uranium-thorium deposit (Aldan region of the Republic of Sakha), characterized by different content of radionuclides and, accordingly, different y-background. On the dumps of the deposit, 5 test sites were laid, having a background of 20, 60,100,750 and 1000 μR/h, respectively. Registration of the y-background was carried out with a SRP-68-01 dosimeter. In this range of y-background values, shrub alder (Duscheciafruticosa) is widespread. On test plots, photosynthetic activity was determined in the leaves of shrub alder (in vivo) by taking into account carbon dioxide (labeled with 14C) in the air flow that passed through a certain area of ​​the leaf [4]. At the same time, alder leaves and mixed samples of fine earth were collected from the upper root-inhabited soil layer (0-10 cm). The samples were dried to an air-dry state to determine the following biochemical parameters under laboratory conditions. In dry leaves, the total content of low molecular weight antioxidants (LMAO) and the activity of ribulose-1,5-diphosphate carboxylase (RuBPC) [5], the activity of superoxide dismutase (SOD) [6], as well as the content of chlorophyll by the spectrometric method [7] were determined. The content of uranium (U) and thorium (Th) radionuclides was determined in air-dry samples of fine earth and dry leaves of shrub alder using an ISP “Element” plasma mass spectrometer (Finnigan MAT, Germany) with inductively coupled plasma; and in soil samples - the activity of hydrolytic and redox enzymes (urease, invertase, catalase, polyphenol oxidase) [8, 9,ten].

Experiments were carried out in 4 replicates. The significance of the difference between the arithmetic means was determined by calculating the standard deviations and confidence intervals for a given quantitative value of the sample [11]. When determining biochemical parameters, the statistical spread was determined by applying a 1% error to the method.

Results and discussion. The development of uranium deposits in the territory of South Yakutia was accompanied by the extraction of rocks enriched with heavy natural radionuclides onto the day surface. Entering the environment, they are involved in the biological cycle, affecting all biotic components of the ecosystem. Soil microorganisms, which have a powerful apparatus for the synthesis of enzymes excreted (for the purpose of extracellular “digestion”) into the external environment, are an effective ecological link in the processes of transformation of various organic and mineral compounds, including various xenobiotics, which are also capable of chelating radionuclides [12 ]. Enzymes of microbiological origin enter the soil, are immobilized by organo-mineral components, and ultimately determine its enzymatic activity. From this point of view, it is relevant to study changes in the enzymatic activity of soils as a factor that determines the conditions for plant growth under the influence of different doses of radiation.

Studies show that radionuclide contamination of soils leads to changes in the abundance and composition of microbial complexes [13]. There is evidence that an increase in the level of natural radiation increases the radioresistance of microorganism cells and the resistance of the latter to lethal doses of radiation [14]. At the same time, the intensity of accumulation of a number of microbial metabolites in soils also changes. It was noted that at high doses of radiation, the vital activity of soil microorganisms is inhibited and the amount of microbial metabolites, DNA, RNA, and free amino acids, decreases in soils [12]. However, there are no data in the literature on the effect of radionuclide contamination on the enzymatic activity of soils. The studied enzymes invertase, urease, catalase, and polyphenol oxidase play an important role in the material and energy metabolism of soils, catalyzing the hydrolysis of carbohydrates and nitrogenous compounds, as well as the redox transformations of hydrogen peroxide and phenols.

Soil enrichment with humus is an important factor determining its enzymatic activity. More humus soils tend to be more active. As our studies have shown,

samples of fine earth, other things being equal, differed not only in different levels of radioactivity, but also in unequal humus content (from 3.52 to 11.86%). In order to level this difference, the activity of enzymes was expressed not only in terms of 1 g of air-dry soil, but also in terms of 100 mg of humus. In our opinion, this allows a more correct comparison of the studied samples.

The results of the study of the enzymatic activity of soils of dumps in the range of increased PY, RF from 20 to 1000 μR/h are shown in fig. 1 (the abscissa shows the values ​​of the radiation background, the ordinate shows the activity of the corresponding soil enzymes). The data obtained indicate that radioactive contamination reduces the level of enzymatic activity of all four studied (both hydrolases and oxido-reductases) soil enzymes. The sharpest decrease in activity was noted for invertase and catalase. Invertase activity decreases by about 3 times already at a minimally elevated background of -60 μR/h, compared with the control (20 μR/h; Fig. 1A). At PERF 100 μR/h, a 3-fold decrease in catalase activity was recorded (Fig. 1B). Urease and polyphenol oxidase activities decreased relative to the control, by 3+4 and 2 times, respectively, only at PERF 1000 μR/h (Fig. 1 C, D).

The decrease in the enzymatic activity of soils, apparently, is a consequence of the inhibition of soil microflora as a result of an increase in the content of radionuclides. According to published data, at radionuclide contamination above 800 μR/h, the content of fungal and bacterial biomass, the amount of DNA, RNA, amino acids, and amine nitrogen in soils decrease [12]. At a lower level of pollution - in the range from 700 to 800 μR/h - fluctuations of these parameters are recorded, which are multidirectional. Moreover, there is not always a complete correspondence between the amount of microbial biomass, the content of microbial metabolites in the soil and radionuclides. Not all metabolites can be directly related to radiation exposure. Such a relationship has been shown for DNA, RNA and bacterial biomass [12]–.

In tab. Table 1 presents data on the content of uranium and thorium in the soil and leaves of shrub alder growing under conditions of different values ​​of PERF, as well as the transfer coefficients of the main radionuclides. It can be seen that the increase in the γ-background is due to an increase in the uranium content in the studied soil samples (except for 100 μR/h). At

y-background 1000 μR/h, the content of and in the soil increases 90 times, and in the leaves of plants - 1560 times. The transition coefficient in the "soil-plant" system at this point of the study was 28. It should be noted that the content of thorium both in the soil and in the leaves was insignificant and did not change regularly depending on the level of PERF.

Uranium is not only a source of ionizing radiation, but also a toxic heavy metal capable of entering into various chemical reactions with the formation of very biochemically active compounds, for example, Ca (UO2) 2PO4, pH20, and metallic uranium can react with almost all atmospheric components , hydrosphere, and many trace elements [14]. The increased content of uranium in the leaves could not but affect the biochemical processes occurring in them.

To assess the degree of effect of PERF on the antioxidant status of plant leaf cells, the content of low molecular weight antioxidants and the activity of enzymatic antioxidants were measured. It has been established that at γ-backgrounds from 20 to 1000 μR/h, the content of HMAO does not change statistically significantly. The activity of SOD, which is an enzymatic membrane antioxidant, increases by 1.2 and 2.0 times at a γ-background value of 100 and 750 μR/h, respectively. Accordingly, the calculated values ​​of caosis with these backgrounds are also higher by 10-50% than in the control (table 2). Previously, it was shown that long-term growth of a number of plant species under PERF conditions leads to an increase in their viability, especially in the range of γ-background values ​​from 100 to 750 µR/h. Moreover, the preservation of cell stability is achieved by activating antioxidant defense systems: either by increasing the content of HMAO, or by activating SOD [1, 2].

To evaluate photosynthetic processes in shrub alder leaves, the following characteristics were studied: chlorophyll content, intensity of photosynthesis, activity of ribulose-1,5-diphosphate carboxylase. The content of chlorophyll in the leaves affects the productivity of plants, but the potential of the plant depends on the intensity of photosynthesis. It is known that the intensity of photosynthesis depends on a large number of factors: illumination, carbon dioxide content, watering, temperature, etc. In nature, a plant experiences all these factors simultaneously, some of which affect the light phase, while others affect the dark phase of photosynthesis [15 ].

It has been established that in the leaves of shrub alder at values ​​of γ-background of 750 and 1000 μR/h, the content of chlorophyll decreases from 0.9 to 0.6, respectively (Table 2). At the same time, the intensity of photosynthesis with PERF above 60 μR/h statistically significantly increases by 40–80%. It is known that plants of different species, placed in optimal conditions, have approximately the same intensity of photosynthesis. Differences appear only when they are exposed to a stress factor [16]. Therefore, it can be assumed that growth conditions with γ-backgrounds above 60 μR/h are stressful for alder shrub and primarily affect the intensity of photosynthesis. Ribulose diphosphate carboxylase, which is the key enzyme of photosynthesis and catalyzes the reaction of carbon dioxide addition to ribulose-1,5-diphosphate, increases its activity by 1.5+2.0 times (relative to control) with an increase in y-background (relative to control) with an increase in PERF from 60 to 1000 μR /h (Table 2). It is known that under the influence of any damaging factor (for example, high temperature), an imbalance in the mechanisms of the photosynthetic apparatus that regulate the optimal distribution of light energy between photosystems can occur [16]. Our results show that an increase in the radiation background is such a factor leading to similar rearrangements in the photosynthetic apparatus of shrub alder leaves.


1. It has been established that as the uranium content in soil increases from 6.3 to 564 mg/kg, its amount in plant leaves increases from 0.01 to 15.6 mg/kg. While thorium practically does not pass into sheet tissue.

2. It has been shown that radioactive contamination with natural radionuclides in the studied concentration range (the increase in γ-background is from 20 to 1000 μR/h) reduces the level of enzymatic activity of the studied soils, both hydrolases and oxidoreductases (invertases, ureases, catalases and polyphenol oxidase) by 2.0+3.5 times. Moreover, the activity of all the studied enzymes (except invertase) changes non-linearly with the growth of PERF, reaching a maximum at 60 μR/h (urease, catalase) or 100 μR/h (polyphenol oxidase), which is 15+45% higher than the activity values ​​of the corresponding enzymes in the control ( at 20 µR/h).

3. It has been established that with an increase in the y-background of growth from 20 to 1000 μR/h, the content of low-molecular antioxidants and chlorophyll in alder leaves does not change statistically significantly. While the activity of SOD changes non-linearly, reaching a maximum (200% of control) at 750 μR/h. Such indicators of the photosynthesis process as its intensity (increase by 40–80%) and the activity of ribulose-1,5-diphosphate carboxylase (>2 times) change non-linearly, reaching a maximum at 100 μR/h. This, apparently, should be considered as a response, adaptive reaction of the plant organism to the actions of the radioactive environmental factor.

Fig. 1. Enzymatic activity of soils depending on the level of γ-background:

A - invertase activity [mg. glitch/g*h]; B - urease activity [mg 1>W47g * 24 h]; B - catalase activity [ml 02 / g * min]; G - activity of polyphenol oxidase [mg benzox./10g h].

On the abscissa axis - the value of the y-background [μR/h]; along the y-axis, the activity of enzymes

Table 10003

with increased natural radiation background

U, mg/kg to Th, mg/kg to transition

µR/h in soil 1 in leaves transition in soil in leaves

20 6. 3±0.01 0.01 ±0.01 0.001 4.8±0.04 0.02±0.01 0.004

60 32.8±0.3 0.89±0.01 ■ 0.027 0.8±0.01 0.03± 0.01 0.04

100 19.1±0.2 1.69±0.01 0.088 0.6±0.01 0.01±0.01 0.01

750 121.9±1, 2 2.27±0.01 0.019 2.2±0.02 - -

1000 564.2±5.3 15.59±0.01 0.028 4.5±0.04 0.01±0.01 0.003

Table 2

Values ​​of the content of low molecular weight antioxidants, superoxide dismutase activity, total antioxidant protection coefficient, chlorophyll content, intensity of photosynthesis and activity of ribulose-1,5-diphosphate carboxylase in shrub alder leaves (normalized relative to control)

μR/h HMAO SOD c a03 Chlorophyll content Rate of photosynthesis Rubisco

20 1.0 1.0 1.0 1.0 1.0 1.0

60 0.9 1.0 1.0 1.0 1.4 1.5

100 0.91.2 1.1 1.0 1.8 1.9

750 0.9 2.0 1.5 0.9 1.6 1.7

1000 1.0 1.0 1.0 0, 6 1.4 2.0


1. Filippov E.V. Physiological and biochemical assessment of the resistance of the genome of wild plants to the action of radiation and non-radiation stress factors of Yakutia: Abstract of the thesis. dis... cand. biol. Sciences. - Yakutsk, 2000.-45 p.

2. Zhuravskaya A.N. Adaptation to extreme environmental conditions and radiosensitivity of plants (radioecological studies): Abstract of the thesis. dis... dr. of biol. Sciences. - M., 2001. - 45 p.

3. Maslova KI. Influence of the ecological factor of increased natural radioactivity on the organism of murine rodents // Radioecology of Vertebrate Animals. - M.: Nauka, 1978. - S. 33-59.

4. Maksimov T.Kh. Ecological and physiological studies of barley photosynthesis in Yakutia: Abstract of the thesis. dis... cand. biol. Sciences. - M., 1989. - 20 p.

5. Asatiani B.C. Enzymatic methods of analysis. - M.: Nauka, 1969. - 740 p.

6. Constantine N.G., Stanley K.R. Superoxide Dismutases in hanger plants // Plant Physiol. 1977.-V.59. -P. 565-569.

7. Large workshop on plant physiology. -M.: Higher School, 1978. -408 p.

8. Khaziev F.Kh. Enzymatic activity of soils. -M.: Nauka, 1976.-S. 20-56.

9. Khaziev F.Kh., Agafonova Ya.M., Gulko A.E. Accelerated colorimetric method for determining soil invertase activity // Eurasian Soil Science. - 1988. -№11.-186 p.

10. Khaziev F.Kh. Methods of soil enzymology. -M.: Nauka, 1990.-S. 171-197.

I. LakinG.F. Biometrics. -M.: Higher school, 1980. -293 p.

12. Efremov A.L. Indication of radionuclide contamination of coniferous forests according to the activity of soil microbiota // Soil Science. - 1997. - No. 11. - S. 743-749.

13. Zhdanova N.N., Vasilevskaya A.I., Zakharchenko V.A., Artyshkova L.V., Nakonechnaya L.T. Features of the microbiota of soils contaminated with radionuclides in the zone of influence of the Chernobyl nuclear power plant (1986 - 1992) // Microbulopchny journal. - 1994. - T. 56. - No. 2. - P. 427.

14. Popular library of chemical elements. - M.: Nauka, 1974. - 237 p.

15. Belikov P.S., Dmitrieva G.A. Plant Physiology - M.: RUDN, 1992. - 248 p.

16. Veselova T. V., Veselovsky V.A., Chernavsky D.S. stress in plants. - M.: Publishing House of Moscow. un-ta, 1993. -143 p.

This work was financially supported by the Russian Foundation for Basic Research,

project No. 03-04-96044 "r2003arktika_a".

Paanajärvi National Park » Contests

We would like to remind you that visitors of our site without age restrictions are invited to participate in the contests. By submitting works to the competition, the participant agrees to the processing of personal data, as well as to the use and publication of articles and photographs. The contributor is also responsible for the copyright of the work.

Applications for participation in competitions and competitive works are accepted until May 30, 2016 by e-mail of the organizer: [email protected] The application must indicate the name of the competition, the name of the work and contact details (participant's full name, place of work / study, address, contact phone number, e-mail).

The results of the competitions and the best works will be published on the official website of the Paanajarvi National Park June 05, 2016 - World Environment Day. Ecologist Day . Also, the best photographs will be placed at the exhibition visit center of the organization.

Additional information can be obtained by phone: 8 (814 39) 48 507; 8 (921) 221 30 55

Competition No. 1 - "Biogeocenosis in photographs"

The purpose of the competition: to focus the attention of the population on the need to preserve the flora and fauna of our region, the preservation of the integrity of which is in our hands.

The participant's work must be submitted in electronic form and framed in a photo wall with a file document attached to it containing a description of the selected ecosystem option (biogeocoenosis). It can be a biogeocenosis of a forest, tundra, lakes, swamps, meadows.

The scheme of biogeocenosis that you see in the picture is an example of a photo wall, in each window of which there should be a photo or collage that replaces each of the sections presented here.

All photographs of your work must be taken on the territory of the Republic of Karelia.

Example: forest biogeocenosis can be as follows: Section "atmosphere" is replaced by a photograph thunderclouds , under the influence of which the soil is moistened, earthworms (photo) immediately set to work, loosening, processing dead plants ( needles, leaves, herbs) is soil-soil section ; microorganisms (nodule bacteria) have their positive effect, but we can only see them under a microscope, which is more difficult to photograph and is the only section of your photographic work that you are allowed to draw. You can draw microorganisms, bacteria or the result of their action on the soil - for example, the root of a plant and photograph your drawing. Nodule bacteria are able to assimilate free nitrogen from the air and convert it into mineral salts available to plants. This favorably affects the soil under alder, which often contains several times more nitrogen than it is available under other species. Element Vegetation Alder (photo). black grouse feed on alder earrings (photo) - representative of section "animal population".

Five components of biogeocenosis are found. Let's try to exclude one of them - earthworms. Up to 5 million worms can live on one hectare of forest soils, which provide significant benefits to the entire forest. Soil animals begin the processing of organic material (dead plants and animals), bacteria and fungi, in turn, complete this work, converting organic residues into minerals available to plants. Mineral salts are used by plants, animals eat plants - the circulation of substances in the biogeocenosis is carried out. But let's not forget that this cycle would not have been possible without the influence of the atmosphere, from which nodule bacteria absorb nitrogen.

The contestant must demonstrate by his work the interconnection of all components of the biogeocenosis and the impossibility of the existence of the presented ecosystem with the exclusion of even one of its components.

In addition to working in electronic form, photographs are submitted as separate files in JPEG format. To further check and exclude the presence of plagiarism. Each photograph must contain technical information (ie camera, lens, aperture, shutter speed, ISO, any special equipment used).

Competition No. 2 —

"The best artistic and journalistic work" , the theme of which is the motto of the March of Parks - 2016.

your voice in defense of a living organism.

Works in the following genres can be submitted to the competition: article, essay, essay, etc. The volume of work should be no more than 2 A4 pages, Times New Roman font, size 12, line spacing 1. 5. Photos and illustrations (if any) are submitted as separate files in JPEG format.

Evaluation criteria: disclosure of the topic of the competition, the presence of significant and original ideas related to the purpose of the competition, the completeness and accuracy of the assessment of the current situation within the framework of the competition, the quality of the text (style of presentation, literacy).

Competition No. 3 -

Crossword "Biodiversity of the native land".

We offer you to get acquainted with interesting facts about the life of the animal and plant world of our region, test your knowledge and solve a crossword puzzle, after solving which you can read part of the motto of the March of Parks - 2016.

Horizontal: 1. The name of a flower pollinated by bumblebees but not by bees. 3. This tree is called a "chameleon", because after felling there is a rapid change in the color of the wood from white to reddish. 6. What plants are called barometers of air purity? 15. A bird that loses its hearing while singing. 17. The most ancient species of insects that appeared on Earth more than 100 million years ago. Today, this insect lives all over the world except for Iceland, Greenland and Antarctica. 18. A bird of prey from the falcon family, lives on all continents except Antarctica. Its speed reaches 320 km / h. 19. A small genus of flowering plants in the Heather family. Usually they are deciduous shrubs that creep along the ground. 23. A bird that is called a "grasshopper" for its dexterous jumps along the branches, "a big one" for its size, and a "zinziver" for its sonorous song. 24. What is the name of the animal, whose paws are turned "palms" out? 25. The smallest mammal in our country. 27. A semi-aquatic predator, on the muzzle and knees of which there are so-called "vibrissae", thanks to them the animal catches the smallest movement in the water and receives information about prey.

Vertical: 2. The name of the mammal with the fastest pulse. 4. The family of this animal stores 30 cubic meters of wood for the winter. 5. The needles of this plant contain 7 times more vitamin C than lemon. 7. Wood, the wood of which is resistant to rot, therefore it is used for underwater structures, in shipbuilding. 8. A branched freshwater crustacean that does not have a circulatory system. It is a natural filter of fresh water. 9. What are the names of organisms that combine the characteristics of plants and animals? 10. 20 thousand years - this is the age of the most ancient rock paintings with images of this predatory animal. The drawings were found in southern Europe. 11. A bird whose male changes color 4 times during the year. 12. A large beetle that exterminates the caterpillar of pests. 13. Predatory animal. He has very sharp hearing and vision. The ancient Greeks believed that this predator could see through objects. 14. The most recognizable of the poisonous mushrooms. Its companions are boletus and porcini mushrooms.

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