Study type and plant litter identity modulating the response of litter decomposition to warming, elevated CO2, and elevated O3: A meta-analysis

Plant litter decomposition is one of the most important ecosystem carbon flux processes in terrestrial ecosystems and is usually regarded as sensitive to climate change. The goal of the present study was to examine the effects of changing climate variables on litter decomposition. By synthesizing data from multiple terrestrial ecosystems, we quantified the response of the litter decomposition rate to the independent effects of warming, elevated carbon dioxide (CO2), elevated ozone (O-3), and the combined effects of elevated CO2+elevated O-3. Across all case studies, warming increased the litter decomposition rate significantly by 4.4%, but this effect could be reduced as a result of the negatively significant effects of elevated CO2 and elevated CO2+elevated O-3. The combined effects of elevated CO2+elevated O-3 decreased the litter decomposition rate significantly, and the magnitude appeared to be higher than that of the elevated CO2 per se. Moreover, the study type (field versus laboratory), ecosystem type, and plant litter identity and functional traits (growth form and litter form) were all important moderators regulating the response of litter decomposition to climate warming and elevated CO2 and O-3. Although litter decomposition rate may show a moderate change as a result of the effects of multiple changing climate variables, the process of litter decomposition would be strongly altered due to the differing mechanisms of the effects of each climate change variable, suggesting that the global carbon cycle and biogeochemistry could be substantially affected. Key Point