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

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 (C_seq), both now and in the future, remains uncertain. 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 C_seq in response to warming. 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 C_seq was the result of the net balance between increases in vegetation and litter C (111.2 g m⁻²) and decreases in soil C (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 C_seq, with the changes in C:N ratios in soil, litter and vegetation as the major contributors, followed by N redistribution, whilst a decrease in total N had a negative effect on C_seq. 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. [ABSTRACT FROM AUTHOR]