Soil [N] modulates soil C cycling in CO-fumigated tree stands: a meta-analysis W. I. J. Dieleman et al. Elevated CO and soil N effects on C cycling.

Under elevated atmospheric CO concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta-analysis to test the hypotheses that: (1) elevated atmospheric CO stimulates soil C inputs more than C losses, resulting in increasing soil C stocks; and (2) that these responses are modulated by N. Our results confirm that elevated CO induces a C allocation shift towards below-ground biomass compartments. However, the increased soil C inputs were offset by increased heterotrophic respiration (Rh), such that soil C content was not affected by elevated CO. Soil N concentration strongly interacted with CO fumigation: the effect of elevated CO on fine root biomass and -production and on microbial activity increased with increasing soil N concentration, while the effect on soil C content decreased with increasing soil N concentration. These results suggest that both plant growth and microbial activity responses to elevated CO are modulated by N availability, and that it is essential to account for soil N concentration in C cycling analyses. [ABSTRACT FROM AUTHOR]