An assessment of soil enrichment by actinorhizal N2fixation using δ15N values in a chronosequence of deglaciation at Glacier Bay, Alaska (original) (raw)
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Soil Biology and Biochemistry, 1994
The role of both actinorhizal and leguminous N,-fixing plants during primary succession within glacial forelands has received much attention, but there are few estimates of the contribution of fixed N to neo-glacial substrates. The main objectives of our work were (i) to assess the N,-fixing ability of three Dryas taxa across a chronosequence of ca 135 yr of post neo-glacial recession, and (ii) to establish whether Dryas serves as a source of N for non-N,-fixing species. The mineral N pool was highly limited across the sere and increased from 0.3 to 1.3 ng g-' of soil over the chronosequence.
Environmental Pollution, 2018
While numerous studies have examined the effect of N deposition on ecosystem N retention, few have analyzed the involvement of plant species and climate warming in this process. We experimentally investigated the effects of increasing N deposition (N exo) and climate warming on the fate of N exo in a subalpine meadow and established the involvement of plant species. Using N tracer, we tracked N exo sprayed on the vegetation in belowground and aboveground plant biomasses (AGB) and in bulk soil over three growing seasons. We assessed the N exo absorption capacity of plant species and the contribution of N exo to their AGB N pool. The meadow retained a large proportion of N exo (≈ 65%, mostly in AGB) for depositions up to four times the background N rate. N exo present in the meadow compartments in year 2 was still present in year 3, suggesting that the ecosystem was unsaturated after three years of high N input. N exo retention resulted more from an increase in N concentration in plant tissues than from the increase in AGB. The species-specific N exo absorption capacity was inversely related to their AGB N concentration. N exo accounted for up to 40% of total AGB N depending on the species and the N treatments. The contribution of species to ecosystem N exo retention more contingent on their AGB than on their relative cover in the community, ranked as follows: C. vulgaris (14.0%) > N. stricta (7.0%) > other Poaceae = C. caryophyllea (2.5%) > other Eudicotyledons (1.5%) > non-vascular species = P. erecta > Fabaceae (0.8-0.2 %). Climate warming increased AGB and decreased tissue N concentration. No warming-N exo interaction was observed. Thus, Pyrenean subalpine meadows that have not undergone a decline in plant species richness in recent decades paradoxically display a high potential to sequester atmospheric N deposition.
Nitrogen fixation in the High Arctic: a source of ‘new’ nitrogen?
Biogeochemistry, 2017
Biological nitrogen (N 2) fixation performed by diazotrophs (N 2 fixing bacteria) is thought to be one of the main sources of plant available N in pristine ecosystems like arctic tundra. However, direct evidence of a transfer of fixed N 2 to non-diazotroph associated plants is lacking to date. Here, we present results from an in situ 15 N-N 2 labelling study in the High Arctic. Three dominant vegetation types (organic crust composed of free-living cyanobacteria, mosses, cotton grass) were subjected to acetylene reduction assays (ARA) performed regularly throughout the growing season, as well as 15 N-N 2 incubations. The 15 N-label was followed into the dominant N 2 fixer associations, soil, soil microbial biomass and nondiazotroph associated plants three days and three weeks after labelling. Mosses contributed most to habitat N 2 fixation throughout the measuring campaigns, and N 2 fixation activity was highest at the beginning of the growing season in all plots. Fixed 15 N-N 2 became quickly (within 3 days) available to non-diazotroph associated plants in all investigated vegetation types, proving that N 2 fixation is an actual source of available N in pristine ecosystems.
Oecologia, 1993
The dynamics of nitrogen supply was investigated for blue-green and green algae from Smith Lake and other freshwaters of subarctic and arctic Alska. The natural abundance of 15N (defined as δ15N) of six N2-fixing blue-green algae was 1.0±%o(X±SE), indicating supply of metabolic nitrogen from atmospheric N2 (δ15N=0.0). The δ15N of six green algae showed an average of 6.6±4.5%o, which is significantly higher than δ15N of N2-fixing blue-green algae from the same waters, reflecting the utilization of dissolved inorganic nitrogen (DIN). Nitrogen-fixing algae also showed higher nitrogen content (7.1±2.1%) than non-N2-fixing algae (2.9±1.5%). The δ15N of a bloom-forming species, Anabaena flos-aquae (Lyngb.) Breb. in Smith Lake showed no significant interannual variations during a three-year study period. The changes in δ15N during each bloom were probably due to variations in the 15N composition of DIN and in the proportional uptake of DIN and N2 fixation. An estimation of the fractional contribution of atmosphere-derived nitrogen (ADN) from δ15N indicated that A. flos-aquae obtained 58–75% of its nitrogen by N2 fixation. This technique agreed with the result obtained using a 15N2 enrichment method. The δ15N of the presumed N2-fixing terrestrial plant was similar to that of the atmospheric N2, whereas the δ15N of the presumed non-N2-fixing terrestrial plants reflected their nitrogen sources.
Arctic, Antarctic, and Alpine Research, 2002
The influence of environmental factors on the nitrogen fixation activity in soil and vegetation samples from different types of plant communities from the Sassen Valley (78°N, 16°E), Svalbard, Norway, was measured under controlled laboratory conditions using the acetylene reduction assay throughout the summers of 1997 and 2000. Samples for study were chosen from six sites along a 2-km-Iong transect representing different types of arctic vegetation. The influence of temperature, soil water content, and light intensity on acetylene reduction rates was studied. Samples from all sites showed low and almost constant acetylene reduction rates between 0 and 100e. Above 10°C the activity of all samples increased rapidly and reached its maximum at about 25 and 32°C for the samples with free-living cyanobacteria and moss-associated cyanobacteria, respectively. There was a significant water-dependent increase of acetylene reduction activity for all types of vegetation. The samples showed a clear response to varying light conditions, i.e. a rapid decrease in acetylene reduction rates when light intensity decreased from 140 to 80 urnol m? S-I depending on the type of vegetation.
Nutrient cycling in …, 2000
Biological nitrogen fixation (BNF) associated with trees and shrubs plays a major role in the functioning of many ecosystems, from natural woodlands to plantations and agroforestry systems, but it is surprisingly difficult to quantify the amounts of N 2 fixed. Some of the problems involved in measuring N 2 fixation by woody perennials include: (a) diversity in occurrence, and large plant-to-plant variation in growth and nodulation status of N 2 -fixing species, especially in natural ecosystems; (b) long-term, perennial nature of growth and the seasonal or yearto-year changes in patterns of N assimilation; and (c) logistical limitations of working with mature trees which are generally impossible to harvest in their entirety. The methodology which holds most promise to quantify the contributions of N 2 fixation to trees is the so-called ' 15 N natural abundance' technique which exploits naturally occurring differences in 15 N composition between plant-available N sources in the soil and that of atmospheric N 2 . In this review we discuss probable explanations for the origin of the small differences in 15 N abundance found in different N pools in both natural and man-made ecosystems and utilise previously published information and unpublished data to examine the potential advantages and limitations inherent in the application of the technique to study N 2 fixation by woody perennials. Calculation of the proportion of the plant N derived from atmospheric N 2 (%Ndfa) using the natural abundance procedure requires that both the 15 N natural abundance of the N derived from BNF and that derived from the soil by the target N 2 -fixing species be determined. It is then assumed that the 15 N abundance of the N 2 -fixing species reflects the relative contributions of the N derived from these two sources. The 15 N abundance of the N derived from BNF (B) can vary with micro-symbiont, plant species/provenance and growth stage, all of which create considerable difficulties for its precise evaluation. If the%Ndfa is large and the 15 N abundance of the N acquired from other sources is not several δ 15 N units higher or lower than B, then this can be a major source of error. Further difficulties can arise in determining the 15 N abundance of the N derived from soil (and plant litter, etc.) by the target plant as it is usually impossible to predict which, if any, non-N 2 -fixing reference species will obtain N from the same N sources in the same proportions with the same temporal and spatial patterns as the N 2 -fixing perennial. The compromise solution is to evaluate the 15 N abundance of a diverse range of neighbouring non-N 2 -fixing plants and to compare these values with that of the N 2 -fixing species and the estimate of B. Only then can it be determined whether the contribution of BNF to the target species can be quantified with any degree of confidence. This review of the literature suggests that while the natural abundance technique appears to provide quantitative measures of BNF in tree plantation and agroforestry systems, particular difficulties may arise which can often limit its application in natural ecosystems.
Arctic, Antarctic, and Alpine Research, 2006
Atmospheric nitrogen (N) fixation is a key N input to arctic ecosystems, but relatively few estimates of annual N-fixation rates are available. We measured N-fixation of plant-soil cores by the acetylene reduction technique at different topographic positions in an upland tundra watershed, Imnavait Creek, through two growing seasons in order to evaluate spatial and temporal variation in N-fixation. We also examined the effects of light and temperature on N-fixation to estimate annual N-fixation rates of surface soil in this watershed using field meteorological data. Surface soil at Imnavait Creek had significant acetylene reduction potential throughout the watershed (generally 6 to 10 lmol C 2 H 4 m À2 h À1 ), indicating that N-fixing organisms were present everywhere. Although acetylene reduction potential was roughly constant through the growing season, moisture, temperature and light intensity strongly affected the measured acetylene reduction rates in laboratory incubations. In addition, the relatively few samples that included the lichen, Peltigera apthosa, had significantly greater acetylene reduction potential, although the overall influence of Peltigera on N-fixation in this watershed seems to be small. The N input via N-fixation at Imnavait Creek was estimated at 80 to 131 mg N m À2 yr À1 , indicating that N-fixation contributed 85 to 90% of total watershed N inputs.
Nitrogen nutrition and isotope differences among life forms at the northern treeline of Alaska
Oecologia, 1994
Natural abundances of nitrogen isotopes, ~15N, indicate that, in the same habitat, Alaskan Picea glauca and P. mariana use a different soil nitrogen compartment from the evergreen shrub Vaccinium vitis-idaea or the deciduous grass Calamagrostis canadensis. The very low 615N values (-7.7 %0) suggest that (1) Picea mainly uses inorganic nitrogen (probably mainly ammonium) or organic N in fresh litter, (2) Vaccinium (-4.3 %0) with its ericoid mycorrhizae uses more stable organic matter, and (3) Calamagrostis (+0.9 %0) exploits deeper soil horizons with higher 615N values of soil N. We conclude that species limited by the same nutrient may coexist by drawing on different pools of soil N in a nutrient-deficient environment. The differences among lifeforms decrease with increasing N availability. The different levels of 615N are associated with different nitrogen concentrations in leaves, Picea having a lower N concentration (0.62 mmol g-I) than Vaccinium (0.98 mmol g-l) or Calamagrostis (1.33 mmol g-l). An extended vector analysis by Timmer and Armstrong (1987) suggests that N is the most limiting element for Picea in this habitat, causing needle yellowing at N concentrations below 0.5 mmol g-1 or N contents below 2 mmol needle-1. Increasing N supply had an exponential effect on twig and needle growth. Phosphorus, potassium and magnesium are at marginal supply, but no interaction between ammonium supply and needle Mg concentration could be detected. Calcium is in adequate supply on both calcareous and acidic soils. The results are compared with European conditions of excessive N supply from anthropogenic N depositions.
Ecosystems, 2008
For the first time in an arctic long-term warming and fertilization experiment, the short-term (days) and longer-term (month and year) nitrogen (N) uptake and allocation in plants, microbes, and soil pools were studied, with 15 N-labeling of an organic nitrogen form, glycine. The long-term warming and fertilization had no marked effect on soil inorganic N content, but both dissolved organic N (DON) and plant biomass did increase after fertilization. Soil microbes initially immobilized most of the added 15 N, but in the following months, they lost two-thirds, while label concentration in plants increased. After a year, however, the 15 N recovered in microbes was still 10-fold higher than that in the plant biomass, showing the high importance of soil microbes in nutrient retention in arctic ecosystems, irrespective of the impact of long-term warming or fertilization. The effects of the treatments on the uptake of label by deciduous shrubs and evergreens paralleled that of their N pool sizes, suggesting that their N uptake potential was unaffected by longterm warming and fertilizer addition. Mosses and herbs had high uptake potential but in fertilized plots they took up less 15 N, that is, they were N saturated. The fraction of 15 N in microbes tended to decrease after fertilization, but this was an effect of higher N pool dilution after 1 month and a year, and not due to lower initial uptake. Although the concentration of soil inorganic N did not change after fertilization, both increased DON and the results of the 15 N label addition showed that the N availability in the ecosystem had increased. By contrast, warming had little effect on soil N pools and microbial 15 N uptake, and, hence, had no detectable effects on 15 N accumulation.
Some land-use systems in Saskatchewan, Canada include the nitrogen-fixing trees buffaloberry (Shepherdia argentea Nutt.), caragana (Caragana arborescens Lam.) and sea buckthorn (Hippophae rhamnoides L.). These species provide various ecological functions such as ameliorating soil moisture, light and temperature but little work has been done quantifying biological nitrogen fixation by these species. Greenhouse experiments were conducted to quantify N 2 -fixation using the 15 N natural abundance and the 15 N dilution methods. Buffaloberry failed to form nodules in all but one of the four replicates in the natural abundance experiment. Using the 15 N dilution method, the percentage of N derived from atmosphere (%Ndfa) in the shoot of buffaloberry averaged 64 %. For caragana, the mean %Ndfa was 59 and 65 % and seabuckthorn was 70 and 73 % measured using the natural abundance and dilution methods, respectively. Because of large variability in biomass production between plants grown in the natural abundance experiment and the dilution experiment, the amounts of N 2 fixed also were very variable. Buffaloberry fixed an average of 0.89 g N m -2 ; the average for caragana ranged from 1.14 to 4.12 g N m -2 and seabuckthorn ranged from 0.85 to 3.77 g N m -2 in the natural abundance and dilution experiments, respectively. This corresponds to 16 kg N ha -1 year -1 for buffaloberry; an average of 15-73 kg N ha -1 year -1 in caragana and 11-67 kg N ha -1 year -1 in seabuckthorn. The substantial amounts of N 2 fixed by these species indicate that they have the potential to contribute to the overall N balance in land-use systems in which they are included.