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76 results for “15N”

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edi36/100

Nitrate concentration and 15N signal of Streamwater and Precipitation from Archived Samples: Watershed 3

This data set includes the analysis of 18 Oxygen isotopes in precipitation and streamwater archived samples from watershed 3. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station.

openCC (other)Jan 2020View details →

edi36/100

15N Tracer Study in Grassland and Shrubland at the Sevilleta National Wildlife Refuge, New Mexico (1989-2002)

Because grasses and shrubs may induce different spatial distributions of nutrients in desert soils, this study was initiated to examine the redistribution of nitrogen in grassland and shrubland soils over a long time period. The stable isotope N15 was applied to plots in grassland and shrubland, and the plots were measured annually from 1989-1993 and again in 1999, 2001, and 2002.

openOpenSep 2010View details →

dryad32/100

Natural 15N abundance of bulk soil N, ammonium, and nitrate in soil profiles

Assessment of nitrogen (N) saturation of forests is critical to evaluate how ecosystems will respond to current and future global changes such as N deposition. However, quantifying N saturation remains a challenge. We developed a conceptual model of N saturation stages in forest ecosystems based on i) a hypothetical relative rate of ammonification, nitrification, and denitrification, ii) concentrations of ammonium and nitrate in the soil, and iii) 15N enrichment pattern of bulk soil N, ammonium, and nitrate in the soil profile. We tested the hypotheses using the data from the five forests located at five sites across eastern Asia, including one boreal forest an dtwo temperate forests in northeastern China, one temperate forest in Japan, and one subtropical forest in south China. The fraction of nitrate in total inorganic N (TIN) indicated that the sites represent an N saturation gradient with one boreal forest being least saturated, three temperate forests moderately saturated, and the tropical forest most saturated. The δ15N of bulk soil N increased from topsoil to subsoil more sharply at N-limited sites than at the N-rich sites along the N deposition gradient. We also found distinct 15N enrichment patterns of bulk soil N, ammonium, and nitrate in the soil profile across the study sites. At the least saturated forest, nitrate was more 15N-depleted than ammonium only in the organic soil horizon indicating limited nitrification while the 15N depletion of nitrate than ammonium was observed in the deeper mineral soil in the moderatley and most saturated forests. Furthermore, ammonium was more 15N-depleted than bulk soil N in the least and moderately saturated forests but more 15N-enriched than bulk soil N in the most saturated forest. Our study suggests that soil profile patterns of δ15N of bulk soil N, ammonium, and nitrate provide information about the relative rates of mineralization, nitrification, and denitrification, thus can be an additional measure of N saturation of forest ecosystem across broad environmental gradients.

opencc-zeroDec 2021View details →

dryad32/100

Retention fraction of 15N-labelled deposited ammonium and nitrate in forests

The impacts of enhanced nitrogen (N) deposition on global forest carbon (C) sink and other ecosystem services may depend on whether N is deposited in reduced (mainly as ammonium) or oxidized forms (mainly as nitrate) and the subsequent fate of each. However, the fates of the two key reactive N forms and its contribution to forest C sink is unclear. We conducted ecosystem-scale paired 15N-labelling experiments in nine forests across China to quantify N retention fractions for both deposited ammonium and nitrate, including tropical and sub-tropical forests for the first time. By combining these results with four previous experiments from temperate Europe and North America, here we show that total ecosystem N retention is similar for ammonium and nitrate, but plants consistently take up more of the labelled nitrate than ammonium while soils retain more ammonium than nitrate. Nitrogen retention in plants and soils across sites is predicted by a combination of tree (NPP and woody biomass) and soil (organic layer mass and soil C/N ratios) variables. Greater proportions of deposited N are retained in N-limited ecosystems with low soil N availability and high soil C/N ratios. We estimate that N deposition-induced C sink in forests contributes more than 20% of the total terrestrial C sink. Although less N is deposited in oxidized than reduced state, their total contributions to the global forest C sink are approximately equal due to more efficient use by trees of the oxidized than the reduced form. Our study demonstrates differential fates of reduced and oxidized N deposition that improves current understanding of the C-N interaction in forests and indicates a greater C sink attributable to atmospheric N deposition than previous estimates.

opencc-zeroDec 2020View details →

dryad32/100

15N recovery under ambient and deepened snow treatments

Seasonal differences in plant and microbial nitrogen (N) acquisition are believed to be a major mechanism that maximizes ecosystem N retention. There is also a concern that climate change may interrupt the delicate balance in N allocation between plants and microbes. Yet, convincing experimental evidence is still lacking. Using a 15N tracer, we assessed how deepened snow affects the temporal coupling between plant and microbial N utilization in a temperate Mongolian grassland. We found that microbial 15N recovery peaked in winter, accounting for 22% of the total ecosystem 15N recovery, and then rapidly declined during the spring thaw. By stimulating N loss via N2O emission and leaching, deepened snow reduced the total ecosystem 15N recovery by 42% during the spring thaw. As the growing season progresses, the 15N released from microbial biomass was taken up by plants, and the competitive advantage for N shifted from microbes to plants. Plant 15N recovery reached its peak in August, accounting for 17% of the total ecosystem 15N recovery. The Granger causality test showed that the temporal dynamics of plant 15N recovery can be predicted by microbial 15N recovery under ambient snow but not under deepened snow. In addition, plant 15N recovery in August was positively correlated with and best explained by microbial 15N recovery in March. The lower microbial 15N recovery under deepened snow in March reduced plant 15N recovery by 73% in August. Together, our results provide direct evidence of seasonal differences in plant and microbial N utilization that are conducive to ecosystem N retention, however, deepened snow disrupted the temporal coupling between plant-microbial N use and turnover. These findings suggest that changes in snowfall patterns may significantly alter ecosystem N cycling and N-based greenhouse gas emissions under future climate change. We highlight the importance of better representing winter processes and their response to winter climate change in biogeochemical models when assessing N cycling under global change.

opencc-zeroMay 2022View details →

dryad32/100

Data from: Drivers of foliar 15N trends in southern China over the last century

Foliar stable nitrogen (N) isotopes (δ15N) generally reflect N availability to plants and have been used to infer about changes thereof. However, previous studies of temporal trends in foliar δ15N have ignored the influence of confounding factors, leading to uncertainties on its indication to N availability. In this study, we measured foliar δ15N of 1,811 herbarium specimens from 12 plant species collected in southern China forests from 1920 to 2010. We explored how changes in atmospheric CO2, N deposition and global warming have affected foliar δ15N and N concentrations ([N]) and identified whether N availability decreased in southern China. Across all species, foliar δ15N significantly decreased by 0.82‰ over the study period. However, foliar [N] did not decrease significantly, implying N homeostasis in forest trees in the region. The spatiotemporal patterns of foliar δ15N were explained by mean annual temperature (MAT), atmospheric CO2 (PCO2), atmospheric N deposition, and foliar [N]. The spatiotemporal trends of foliar [N] were explained by MAT, temperature seasonality, PCO2, and N deposition. N deposition within the rates from 5.3 – 12.6 kg N ha-1 yr-1 substantially contributed to the temporal decline in foliar δ15N. The decline in foliar δ15N was not accompanied by changes in foliar [N] and therefore does not necessarily reflect a decline in N availability. This is important to understand changes in N availability, which is essential to validate and parameterize biogeochemical cycles of N.

opencc-zeroJun 2022View details →

zenodo32/100

FIGURES 3–6 in 1H, 13C and 15N resonance assignments of telomeric repeat-binding domain ofArabidopsis thaliana

FIGURES 3–6. Nilotanypus polycanthus sp. n., male. 3. Abdomen. 4. Wing. 5. Tibial spur and pseudospurs on fore leg. 6. Hypopygium, ventral and dorsal view.

opennotspecifiedMay 2006View details →

dryad32/100

Strong non-growing season N uptake by deciduous trees in a temperate forest: A 15N isotopic experiment

Nitrogen (N) is a critical element for vegetation growth and subsequent carbon (C) and nutrient cycling in terrestrial ecosystems. Plant N uptake, the only pathway for plants to directly obtain N from soils, is a bottleneck process for ecosystem C and N cycling. Ecological theories predict that deciduous trees remain dormant and do not take up N during winters as no growth occurs during this season. In this study, we adopted a 15N isotopic experiment to trace N processes throughout the non-growing season in a temperate forest in northern China. The 15N-labeled inorganic N (NH4+ and NO3−) and 13C15N-labeled organic N (glycine and tyrosine) (equivalent to 150 mg 15N m-2) were applied to soils at mid-fall, and the 15N recovery in various components of dominant evergreen and deciduous species was analyzed. We found that soil N transformation remained active in the winter and microbial N immobilization reached its peak in late winter. Surprisingly, deciduous species maintained a high N uptake that was comparable with the evergreen species throughout the non-growing season. Perennial herbs did not take up N until the next spring. All plant species acquired inorganic N and simple amino acids, while only the tree species utilized complex amino acids. Throughout the non-growing season, evergreen and deciduous trees showed higher uptake rates for NH4+ and glycine than NO3− and tyrosine, while deciduous shrubs and herbs showed a stronger preference for NO3− over other N forms. Synthesis: The finding that deciduous trees have strong N uptake in the non-growing season challenges the conventional viewpoint that deciduous trees remain dormant during non-growing seasons. This mechanism might supplement the algorithm in the model representation of N-limited temperate forest ecosystems.

opencc-zeroJul 2021View details →

dryad32/100

Enhanced foliar 15N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds

Determining the abundance of N isotope (δ15N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their 15N signatures remains unclear. Here, the response of δ15N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH4HCO3, urea, and NH4NO3) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ15N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N2-fixing species) showed significantly lower 15N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi, AMF) and C. duriuscula (associated with AMF). Moreover, the foliar δ15N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m-2yr-1. Foliar δ15N values were significantly higher when NH4HCO3 and urea were added than when NH4NO3 was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co-existing plant species in the ecosystem.

opencc-zeroDec 2022View details →

dryad32/100

Data from: In situ 15N-N2O site preference and O2 concentration dynamics disclose the complexity of N2O production processes in agricultural soil

Arable soil continues to be the dominant anthropogenic source of nitrous oxide (N2O) emissions owing to application of nitrogen (N) fertilizers and manures across the world. Using laboratory and in-situ studies to elucidate the key factors controlling soil N2O emissions remains challenging due to the potential importance of multiple complex processes. We examined soil surface N2O fluxes in an arable soil, combined with in-situ high-frequency measurements of soil matrix oxygen (O2) and N2O concentrations, in situ 15N labeling, and N2O 15N site preference (SP). The in situ O2 concentration and further microcosm visualized spatiotemporal distribution of O2 both suggested that O2 dynamics were the proximal determining factor to matrix N2O concentration and fluxes due to quick O2 depletion after N fertilization. Further SP analysis and in situ 15N labeling experiment revealed that the main source for N2O emissions was bacterial denitrification during the hot-wet summer with lower soil O2 concentration, while nitrification or fungal denitrification contributed about 50.0% to total emissions during the cold-dry winter with higher soil O2 concentration. The robust positive correlation between O2 concentration and SP values underpinned that the O2 dynamics were the key factor to differentiate the composite processes of N2O production in in situ structured soil. Our findings deciphered the complexity of N2O production processes in real field conditions, and suggest that O2 dynamics rather than stimulation of functional gene abundances play a key role in controlling soil N2O production processes in undisturbed structure soils. Our results help to develop targeted N2O mitigation measures and to improve process models for constraining global N2O budget.

opencc-zeroMay 2023View details →

dryad32/100