The response of ecosystem carbon and nitrogen pools to experimental warming in grasslands: a meta-analysis

Aims Carbon (C) and nitrogen (N) coupling processes in terrestrial ecosystems have the potential to modify the sensitivity of the global C cycle to climate change. But the degree to which C–N interactions contribute to the sequestration of terrestrial ecosystem C (Cseq), both now and in the future, remains uncertain. Methods In this study we used a meta-analysis to quantitatively synthesize C and N responses from field experiments on grasslands subjected to simulated warming and assessed the relative importance of three properties (changes in ecosystem N amount, redistribution of N among soil, litter, and vegetation, and modifications in the C:N ratio) associated with grassland Cseq in response to warming. Important Findings Warming increased soil, litter, and vegetation C:N ratios and approximately 2% of N shifted from the soil to vegetation and litter. Warming-induced grassland Cseq was the result of the net balance between vegetation and litter C increase (111.2 g m -2) and soil C decrease (30.0 g m -2). Warming-induced accumulation of C stocks in grassland ecosystems indicated that the three processes examined were the main contributors to Cseq, with the change in C:N ratio in soil, litter and vegetation the major contributor, followed by N redistribution, whilst a decrease in total N had a negative effect on Cseq. These results indicate that elevated temperatures have a significant influence on grassland C and N stocks and their coupling processes, suggesting that ecological models need to include C–N interactions for more accurate predictions of future terrestrial C storage.