Effects of carbon turnover time on terrestrial ecosystem carbon storage

Carbon (C) turnover time is a key factor in determining C storage capacity in various plant and soil pools as well as terrestrial C sink in a changing climate. However, the effects of C turnover time on ecosystem C storage have not been well explored. In this study, we compared mean C turnover times (MTTs) of ecosystem and soil, examined their variability to climate, and then quantified the spatial variation in ecosystem C storage over time from changes in C turnover time and/or net primary production (NPP). Our results showed that mean ecosystem MTT based on gross primary production (GPP; MTTECGPP Combining double low line gCpool/GPP, 25.0g2.7 years) was shorter than soil MTT (MTTsoil Combining double low line gCsoil/NPP, 35.5g1.2 years) and NPP-based ecosystem MTT (MTTECNPP Combining double low line gCpool/NPP, 50.8g3 years; Cpool and Csoil referred to ecosystem or soil C storage, respectively). On the biome scale, temperature is the best predictor for MTTEC (2 Combining double low line g0.77, 0.001) and MTTsoil (2 Combining double low line g0.001), while the inclusion of precipitation in the model did not improve the performance of MTTEC 2 Combining double low line g0.76, 0.001). Ecosystem MTT decreased by approximately 4 years from 1901 to 2011 when only temperature was considered, resulting in a large C release from terrestrial ecosystems. The resultant terrestrial C release caused by the decrease in MTT only accounted for about 13.5g% of that due to the change in NPP uptake (159.3g1.45 vs. 1215.4g11.0gC). However, the larger uncertainties in the spatial variation of MTT than temporal changes could lead to a greater impact on ecosystem C storage, which deserves further study in the future.