Temperature Exerted No Influence on the Organic Carbon Isotope of Surface Soil along the Isopleth of 400 Mm Mean Annual Precipitation in China

Abstract. Soil organic carbon is the largest pool of terrestrial ecosystem and its carbon isotope composition is affected by many factors. However, the influence of environmental factors, especially temperature, on soil organic carbon isotope (δ13CSOM) is poorly constrained. This impedes interpretations and application of variability of organic carbon isotope in reconstructions of paleoclimate and paleoecology and global carbon cycling. With a considerable temperature gradient along the 400 mm isohyet (isopleth of mean annual precipitation – MAP) in China, this isohyet provides ideal experimental sites for studying the influence of temperature on soil organic carbon isotope. In this study, the effect of temperature on surface soil δ13C was assessed by a comprehensive investigation from 27 sites across a temperature gradient along the isohyet. This work demonstrates that temperature did not play a role in soil δ13C, this suggests that organic carbon isotopes in sediments cannot be used for the paleotemperature reconstruction, and that the effect of temperature on organic carbon isotopes can be neglected in the reconstruction of paleoclimate and paleovegetation. Multiple regression with MAT (mean annual temperature), MAP, altitude, latitude and longitude as independent variables, and δ13CSOM as the dependent variable, shows that the five environmental factors in total account for only 9 % soil δ13C variance. However, One-way ANOVA analyses suggest that soil and vegetation types are significant influential factors on soil δ13C. Multiple regressions in which above five environmental factors were taken as quantitative variables, vegetation type, Chinese nomenclature soil type and WRB soil type were introduced as dummy variables separately, show that 36.2 %, 37.4 %, 29.7 % of the variability in soil δ13C are explained, respectively. Compared to the multiple regression in which only quantitative environmental variables were introduced, the multiple regressions in which soil and vegetation were also introduced explain more variance, suggesting that soil type and vegetation type really exerted significant influences on δ13CSOM.