Abstract
Abstract. 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; MTTEC_GPP = Cpool/GPP, 25.0 ± 2.7 years) was shorter than soil MTT (MTTsoil = Csoil/NPP, 35.5 ± 1.2 years) and NPP-based ecosystem MTT (MTTEC_NPP = Cpool/NPP, 50.8 ± 3 years; Cpool and Csoil referred to ecosystem or soil C storage, respectively). On the biome scale, temperature is the best predictor for MTTEC (R2 = 0.77, p < 0.001) and MTTsoil (R2 = 0.68, p < 0.001), while the inclusion of precipitation in the model did not improve the performance of MTTEC (R2 = 0.76, p < 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 13.5 % of that due to the change in NPP uptake (159.3 ± 1.45 vs. 1215.4 ± 11.0 Pg C). 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.
Highlights
Rising atmospheric CO2 concentrations and the resultant climatic warming can substantially impact global carbon (C) budget (IPCC, 2007), leading to a positive or negative feedback to global climate change (Friedlingstein et al, 2006; Heimann and Reichstein, 2008)
Among eight typical biomes associated with plant functional types (PFTs, Table 1), the order of ecosystem C storage contribution followed as evergreen needleleaf forest (ENF) (34.84 ± 0.02 kg C m−2) > deciduous needleleaf forest (DNF) (25.30 ± 0.03 kg C m−2) > evergreen broadleaf forest (EBF) (22.70 ± 0.01 kg C m−2) > shrubland (18.29 ± 0.02 kg C m−2) > deciduous broadleaf forest (DBF) (16.51 ± 0.02 kg C m−2) > tundra (14.16 ± 0.02 kg C m−2)/cropland (14.58 ± 0.01 kg C m−2) > grassland (10.80 ± 0.01 kg C m−2)
The order of gross primary production (GPP)-based ecosystem mean C turnover times (MTTs) among biomes differed for ecosystem C storage, with tundra (99.704 ± 6.14 years) > DNF (45.27 ± 2.43 years) or ENF (42.23 ± 2.01 years) > shrubland (27.77 ± 2.25 years) > grassland (26.00 ± 1.41 years) > cropland (14.91 ± 0.40 years) or DBF (13.29 ± 0.68 years) > EBF (9.67 ± 0.21 years)
Summary
Rising atmospheric CO2 concentrations and the resultant climatic warming can substantially impact global carbon (C) budget (IPCC, 2007), leading to a positive or negative feedback to global climate change (Friedlingstein et al, 2006; Heimann and Reichstein, 2008). Projections of Earth system models (ESMs) show a substantial decrease in terrestrial C storage as the world warms (Friedlingstein et al, 2006), but the decreased magnitude is difficult to be quantified due to the complexity of terrestrial ecosystems in response to global change (Chambers and Li, 2007; Strassmann et al, 2008). The response of terrestrial C storage to climate change depends on the responses of C flux and turnover time in various C pools
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