• Energy Research

AbstractDroughts can strongly affect grassland productivity and biodiversity, but responses differ widely. Nutrient availability may be a critical factor explaining this variation, but is often ignored in analyses of drought responses. Here, we used a standardized nutrient addition experiment covering 10 European grasslands to test if full‐factorial nitrogen, phosphorus, and potassium addition affected plant community responses to inter‐annual variation in drought stress and to the extreme summer drought of 2018 in Europe. We found that nutrient addition amplified detrimental drought effects on community aboveground biomass production. Drought effects also differed between functional groups, with a negative effect on graminoid but not forb biomass production. Our results imply that eutrophication in grasslands, which promotes dominance of drought‐sensitive graminoids over forbs, amplifies detrimental drought effects. In terms of climate change adaptation, agricultural management would benefit from taking into account differential drought impacts on fertilized versus unfertilized grasslands, which differ in ecosystem services they provide to society.

AbstractDroughts can strongly affect grassland productivity and biodiversity, but responses differ widely. Nutrient availability may be a critical factor explaining this variation, but is often ignored in analyses of drought responses. Here, we used a standardized nutrient addition experiment covering 10 European grasslands to test if full‐factorial nitrogen, phosphorus, and potassium addition affected plant community responses to inter‐annual variation in drought stress and to the extreme summer drought of 2018 in Europe. We found that nutrient addition amplified detrimental drought effects on community aboveground biomass production. Drought effects also differed between functional groups, with a negative effect on graminoid but not forb biomass production. Our results imply that eutrophication in grasslands, which promotes dominance of drought‐sensitive graminoids over forbs, amplifies detrimental drought effects. In terms of climate change adaptation, agricultural management would benefit from taking into account differential drought impacts on fertilized versus unfertilized grasslands, which differ in ecosystem services they provide to society.

Abstract Since the industrial revolution, accelerated atmospheric nitrogen (N) deposition by human activities have increased N availability in forest ecosystems close to human settlements, potentially causing many nitrogen-limited forests to become nitrogen-saturated, with significant effects on productivity, biodiversity, and biogeochemical cycles. Four decades after recognizing the N saturation problem, however, global patterns of N saturation in forests still remain uncertain. In N-saturated forests, oversupply of N leads to higher N losses including those in form of N2O as compared to N-limited forests, suggesting that the sensitivity of soil N2O emission to N deposition (sN) might be used as an indicator of N saturation. In this study, we modeled the sN of global forests using data from N addition experiments. Testing with field observations on N saturation status, the global patterns of N-limited and N-saturated forests indicated by sN show an accuracy above 70% on global and geographic-regional scales. Our results suggest that 43% of global forests are N-saturated, and the proportions of forests being N-saturated are particularly high in East Asia and Western Europe (over 60%). The produced global map of N-saturated forests sheds light on the spatially varying N availability in forests, which founds a basis for predicting the influence of changing N deposition on forest greenhouse gas emissions and productivity, facilitating optimized environmental management practices for different regions.

Abstract Since the industrial revolution, accelerated atmospheric nitrogen (N) deposition by human activities have increased N availability in forest ecosystems close to human settlements, potentially causing many nitrogen-limited forests to become nitrogen-saturated, with significant effects on productivity, biodiversity, and biogeochemical cycles. Four decades after recognizing the N saturation problem, however, global patterns of N saturation in forests still remain uncertain. In N-saturated forests, oversupply of N leads to higher N losses including those in form of N2O as compared to N-limited forests, suggesting that the sensitivity of soil N2O emission to N deposition (sN) might be used as an indicator of N saturation. In this study, we modeled the sN of global forests using data from N addition experiments. Testing with field observations on N saturation status, the global patterns of N-limited and N-saturated forests indicated by sN show an accuracy above 70% on global and geographic-regional scales. Our results suggest that 43% of global forests are N-saturated, and the proportions of forests being N-saturated are particularly high in East Asia and Western Europe (over 60%). The produced global map of N-saturated forests sheds light on the spatially varying N availability in forests, which founds a basis for predicting the influence of changing N deposition on forest greenhouse gas emissions and productivity, facilitating optimized environmental management practices for different regions.

SummaryInteractions between carbon (C) and nitrogen (N) cycles in terrestrial ecosystems are simulated in advanced vegetation models, yet methodologies vary widely, leading to divergent simulations of past land C balance trends. This underscores the need to reassess our understanding of ecosystem processes, given recent theoretical advancements and empirical data. We review current knowledge, emphasising evidence from experiments and trait data compilations for vegetation responses to CO2 and N input, alongside theoretical and ecological principles for modelling. N fertilisation increases leaf N content but inconsistently enhances leaf‐level photosynthetic capacity. Whole‐plant responses include increased leaf area and biomass, with reduced root allocation and increased aboveground biomass. Elevated atmospheric CO2 also boosts leaf area and biomass but intensifies belowground allocation, depleting soil N and likely reducing N losses. Global leaf traits data confirm these findings, indicating that soil N availability influences leaf N content more than photosynthetic capacity. A demonstration model based on the functional balance hypothesis accurately predicts responses to N and CO2 fertilisation on tissue allocation, growth and biomass, offering a path to reduce uncertainty in global C cycle projections.

SummaryInteractions between carbon (C) and nitrogen (N) cycles in terrestrial ecosystems are simulated in advanced vegetation models, yet methodologies vary widely, leading to divergent simulations of past land C balance trends. This underscores the need to reassess our understanding of ecosystem processes, given recent theoretical advancements and empirical data. We review current knowledge, emphasising evidence from experiments and trait data compilations for vegetation responses to CO2 and N input, alongside theoretical and ecological principles for modelling. N fertilisation increases leaf N content but inconsistently enhances leaf‐level photosynthetic capacity. Whole‐plant responses include increased leaf area and biomass, with reduced root allocation and increased aboveground biomass. Elevated atmospheric CO2 also boosts leaf area and biomass but intensifies belowground allocation, depleting soil N and likely reducing N losses. Global leaf traits data confirm these findings, indicating that soil N availability influences leaf N content more than photosynthetic capacity. A demonstration model based on the functional balance hypothesis accurately predicts responses to N and CO2 fertilisation on tissue allocation, growth and biomass, offering a path to reduce uncertainty in global C cycle projections.