Declines in carbon and nitrogen release from decomposing litter under elevated CO2 in terrestrial ecosystems

Abstract Atmospheric carbon dioxide (CO2) concentrations have been increasing dramatically due to human activities and land use changes, and the CO2 fertilization effect significantly increases global net primary productivity (NPP). However, whether the decomposition of surplus litter input on the soil surface is facilitated by elevated CO2 (eCO2) across a broad range of terrestrial ecosystems is not fully understood. We compiled 227, 85 and 131 paired observations (with and without eCO2) for litter mass loss, carbon (C) and nitrogen (N) release, respectively, during litter decomposition to assess the fate of decomposing litter and C and N release under eCO2 across terrestrial ecosystems. Litter mass loss was decreased by 4.46%, and C and N release were significantly reduced by 6.70% and 3.36%, respectively, under eCO2. This eCO2 effect on litter mass loss was greater in forests (decreased by 7.22%) than in croplands and grasslands. In forests, eCO2 had a greater effect on the decomposition rate of broadleaved than coniferous litter, and root litter was more sensitive than leaf and stem litter. Changes in litter lignin concentration and edaphic factors under eCO2 contributed to these differences in litter decomposition. Greater decreases in litter mass loss and C and N release were found after longer time (6-12 months) than short-term (less than 6 months) CO2 enrichment. A possible consequence is that more litter accumulates on soil surface without being decomposed due to eCO2 in terrestrial ecosystems over longer time periods, resulting in a negative loop in biogeochemical cycles with increasing atmospheric CO2 concentration.