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Nitrogen (N) dynamic is one of the main controlling factors of responses to climate change in N-limited terrestrial ecosystems, which rely on nutrient recycling and retention. In this study we investigate the N partitioning in ecosystem compartments of a grassland heath, and the impact of multiple climate change factors on long-term N retention after 15N pulse labelling. The impacts of elevated carbon dioxide (eCO2), warming and drought and the treatments in combination on ecosystem N retention were investigated in a field scale manipulation experiment. A 6-year time-course was assessed by pulse-labelling with the stable N isotope 15N and by sampling after 1 day, 1 year and 6 years. After 6 years we observed that the total ecosystem retained 42% of the amended 15N across treatments (recovery of the amended 15N in the pool). The fate of the applied 15N was mainly stabilization in soil, with 36% 15N recovery in soil, while the plant compartment and microbial biomass each retained only 1%–2% of the added 15N. This suggests a moderate retention of N, for all treatments, as compared to similar long-term studies of forest ecosystems. A decreased ammonium and vegetation N pool combined with higher 15N retention in the soil under eCO2 treatments suggests that eCO2 promoted processes that immobilize N in soil, while warming counteracted this when combined with eCO2. Drought treatments contrastingly increased the vegetation N pool. We conclude that as the organic soil layer has the main capacity for N storage in a temperate heathland-grassland, it is important for buffering nutrient availability and maintaining a resilient ecosystem. However, the full treatment combination of drought, warming and eCO2 did not differ in 15N recovery from the control, suggesting unchanged long-term consequences of climate change on retention of pulse added N in this ecosystem., Nitrogen (N) dynamic is one of the main controlling factors of responses to climate change in N-limited terrestrial ecosystems, which rely on nutrient recycling and retention. In this study we investigate the N partitioning in ecosystem compartments of a grassland heath, and the impact of multiple climate change factors on long-term N retention after 15N pulse labelling. The impacts of elevated carbon dioxide (eCO2), warming and drought and the treatments in combination on ecosystem N retention were investigated in a field scale manipulation experiment. A 6-year time-course was assessed by pulse-labelling with the stable N isotope 15N and by sampling after 1 day, 1 year and 6 years. After 6 years we observed that the total ecosystem retained 42% of the amended 15N across treatments (recovery of the amended 15N in the pool). The fate of the applied 15N was mainly stabilization in soil, with 36% 15N recovery in soil, while the plant compartment and microbial biomass each retained only 1%–2% of the added 15N. This suggests a moderate retention of N, for all treatments, as compared to similar long-term studies of forest ecosystems. A decreased ammonium and vegetation N pool combined with higher 15N retention in the soil under eCO2 treatments suggests that eCO2 promoted processes that immobilize N in soil, while warming counteracted this when combined with eCO2. Drought treatments contrastingly increased the vegetation N pool. We conclude that as the organic soil layer has the main capacity for N storage in a temperate heathland-grassland, it is important for buffering nutrient availability and maintaining a resilient ecosystem. However, the full treatment combination of drought, warming and eCO2 did not differ in 15N recovery from the control, suggesting unchanged long-term consequences of climate change on retentio

The combination of nitrogen (N) fertilization and straw incorporation has complex influences on soil N transformations and derived nitrous oxide (N2O) emissions. This study aimed to reveal the coupled effects of straw returning forms and N fertilizer management on soil N2O emissions. Here, carbon (C) sources with varied availabilities were supplied by different straw returning forms, including straw, charred straw, and combined application of straw and charred straw. The time gaps between additions of exogenous N and C sources were carried out by managing the timing of N fertilization, including N application simultaneous with or delayed after straw return. Soil N2O emissions under different straw returning forms and their response relationships to soil C, N, microbial biomass, as well as soil pH and oxygen (O2) were explored. Co-application of straw and N fertilizer provided sufficient C and N sources, enhanced the microbial biomass, and consequently increased N2O emissions. Delayed N fertilization could decouple the response of N2O emissions to straw addition, because of constrained N availability and limited pH decline, which decreased the cumulative N2O emissions significantly. Possibly due to straw induced N immobilization coupled with charred straw induced pH elevation, the combined application of straw and charred straw constrained soil N2O emissions compared with straw only application, regardless of N fertilizer management. By shaping the microbial biomass and soil C, N, and O2 dynamics, delayed application of N fertilizer could further enhance the inhibition effect of the charred straw and straw combination on soil N2O emissions. Therefore, the varied straw returning forms and the timing of N fertilization could affect the supply of available C and N, influencing the hot moments of N2O emissions, and the joint addition of straw and ch

Nitrous oxide is an important greenhouse gas and emissions from managed ecosystems are directly correlated to anthropogenic nitrogen input. Here we have measured nitrous oxide emissions from flooded depressions within croplands and from incubated soil samples. We scaled emissions to >20,000 comparable flooded depressions across Zealand in Denmark using a deep-learning approach based on aerial photos and satellite images. We show that flooded depressions within cultivated fields, representing less than 1% of the total cultivated area, can release 80 times more nitrous oxide compared to rest of the fields. Fluxes can remain high for more than two months after fertilisation and can account for 30 ± 1% of the nitrous oxide budget during that period. This highlights the urgent need for assessment of nitrous oxide hotspots, as managing these hotspots appear to represent an important part of the overall greenhouse gas emissions from managed croplands and an efficient mitigation action.

In the Arctic tundra, snowmelt is followed by soil thaw allowing water and dissolved nutrients to move downslope. However, the fate of the released nitrogen (N) remains unclear, which includes the fraction of N that is lost to downslope transport or converted to N gasses. We have quantified the release of NO3− into the soil solution and the loss of gaseous N upon thaw and up to a month after first thaw in an Arctic hillslope in W Greenland. We further investigated which factors of the slope ecosystem that influence the NO3− concentrations and N2O fluxes throughout two snowmelt and growing seasons using a Structural Equation Model (SEM) linking physical, biological and biogeochemical characteristics across the slope. Snowmelt controls growing season onset, but varies in the landscape. To account for this, we normalized the spatiotemporal variation in snowmelt and soil thaw by measuring NO3− release and N2O loss in a controlled laboratory thaw experiment with topsoil cores from along the slope. We furthermore normalized seasonal progression of ecosystem variables in space based on the first day of soil thaw in the field. We tested the variable Day After Soil Thaw (DAST) as the temporal driver in our SEM, and found that season progression is the most important factor to describe patterns in NO3− concentrations and N2O fluxes. We conclude that DAST is a useful tool for analysing seasonal patterns in a spatially heterogeneous snowmelt landscape and between different snowmelt years. When normalizing based on first day of soil thaw, we saw that the decreasing NO3− content over the season did not control the increasing N2O emissions. Rather, nitrification replaced denitrification as the main N2O -source during the growing season, where soil temperatures increased and soil moisture decreased. The gaseous N los

Rationale Stable isotope approaches are increasingly applied to better understand the cycling of inorganic nitrogen (N-i) forms, key limiting nutrients in terrestrial and aquatic ecosystems. A systematic comparison of the accuracy and precision of the most commonly used methods to analyze delta N-15 in NO3- and NH4+ and interlaboratory comparison tests to evaluate the comparability of isotope results between laboratories are, however, still lacking. Methods Here, we conducted an interlaboratory comparison involving 10 European laboratories to compare different methods and laboratory performance to measure delta N-15 in NO3- and NH4+. The approaches tested were (a) microdiffusion (MD), (b) chemical conversion (CM), which transforms N-i to either N2O (CM-N2O) or N-2 (CM-N-2), and (c) the denitrifier (DN) methods. Results The study showed that standards in their single forms were reasonably replicated by the different methods and laboratories, with laboratories applying CM-N2O performing superior for both NO3- and NH4+, followed by DN. Laboratories using MD significantly underestimated the "true" values due to incomplete recovery and also those using CM-N-2 showed issues with isotope fractionation. Most methods and laboratories underestimated the at%N-15 of N-i of labeled standards in their single forms, but relative errors were within maximal 6% deviation from the real value and therefore acceptable. The results showed further that MD is strongly biased by nonspecificity. The results of the environmental samples were generally highly variable, with standard deviations (SD) of up to +/- 8.4 parts per thousand for NO3- and +/- 32.9 parts per thousand for NH4+; SDs within laboratories were found to be considerably lower (on average 3.1 parts per thousand). The variability could not be connected to any single factor but next to errors due to blank contamination, isotope normalization, and fractionation, and also matrix effects and analytical errors have to be considere

In recent years, wildfire frequency and severity has increased in the Arctic tundra regions due to climate change. Pyrogenic organic matter (PyOM) is a product of incomplete combustion of biomass containing nutrients such as nitrogen (N), and is expected to affect ecosystem N cycling during a post-fire recovery period. We investigated effects of fire on soil biogeochemical cycles with a focus on pyrogenic N turnover over two subsequent growing seasons, combined with and without summer warming, in an Arctic heath tundra, West Greenland. The summer warming was achieved by deployment of open top chambers (OTCs). We simulated an in situ tundra fire by removing vegetation and litter, and scorching/heating soil surface followed by the addition of N-15-labelled PyOM (derived from aboveground biomass and litter) to the soil surface in plots with and without summer warming. A darker surface after the simulated fire resulted in an increase of 1.3 degrees C in soil temperature at 5-cm depth over the growing seasons. The fire also caused a nine-fold increase in soil NH4+-N and three-fold increase in soil NO3--N concentrations at 7-cm depth after two years. Tracing the fate of N-15-labelled PyOM, 21 days after its application, showed low N-15 recovery in microbial biomass (0.4%) and total dissolved N (TDN) pools (0.01%). Microbial and root N-15 recovery increased two-fold and 15-fold after one year, respectively, and TDN N-15 recovery increased two-fold after two years, suggesting that relatively recalcitrant N of PyOM can be partly transformed into plantavailable forms over time. Root and TDN N-15 recovery was also significantly higher after two years of summer warming than under ambient temperature conditions, suggesting that summer warming can enhance availability of PyOM-N for recovering plants after the fire. Hence, we conclude that fire-induced PyOM can act as an N source for plant recovery in this Arctic tundra ecosystem for years after the fire, and this N source will

Vådlægning af lavbundsjorde er udset til at spille en vigtig rolle i at rette op på klimaregnskabet. Men det kan tage mellem 15 og 100 år at opnå en klimaeffekt, og den vil være lille og måske negativ de første mange år. Der mangler viden om, hvad der sker., Vådlægning af lavbundsjorde er udset til at spille en vigtig rolle i at rette op på klimaregnskabet. Men det kan tage mellem 15 og 100 år at opnå en klimaeffekt, og den vil være lille og måske negativ de første mange år. Der mangler viden om, hvad der sker.