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. 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 4.5%, and C and N release were significantly reduced by 6.7% and 3.4%, respectively, under eCO₂. This eCO₂ effect on litter mass loss was greater in forests (decreased by 7.2%) 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 the 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.

Key words: elevated CO₂, CO₂ fertilization, litter decomposition, carbon release, nitrogen release