Latitudinal Patterns And Influencing Factors Of Different Soil Organic Carbon Fractions In The Eastern Forests Of China

Soil organic carbon(SOC) is one of the most important pools in forest ecosystems. SOC is an important component on biogeochemical cycles, and it undertakes important process in carbon(C) interaction on terrestrial ecosystem. Understanding its geographic patterns and influencing factors is critical to predict the soil C sequestration and stability. In this study, nine typical forest ecosystems(Jiangfengling, Dinghushan, Jiulianshan, Shengnongjia, Taiyueshan, Donglingshan, Changbaishan, Liangshui, and Huzhong) were selected along the North–South Transect of Eastern China(NSTEC), and covered tropical, subtropical, and temperate climate zones. The content of SOC, easy–oxidized organic carbon(EOC), microbial biomass carbon(MBC), and dissolved organic carbon(DOC), humic acid carbon(HAC), fulvic acid carbon(FAC), humin carbon(HUC), and extractable humus carbon(HEC) was measured in the 0–10–cm soil layer, and climate factors, soil texture, soil microbes, and vegetation biomass were used to explore the latitudinal pattern of SOC fractions in forests and the main factors influencing them. The main conclusions are as following: 1. SOC, EOC, MBC, and DOC contents were 23.12–77.00 g kg–1, 4.62–17.24 g kg–1, 41.92–329.39 mg kg–1, and 212.63–453.43 mg kg–1, respectively. SOC, EOC, and MBC increased exponentially as the latitude increased(P < 0.05), whereas DOC decreased exponentially as the latitude increased(P < 0.05). The SOC and EOC contents in forest soils were in the following order: tropical forest < subtropical forest < temperate forest(P < 0.05), and the order for DOC content was tropical forest > subtropical forest > temperate forest(P < 0.001). The results of the structural equation modeling showed that climate, soil texture, soil microbe, and vegetation biomass significantly affected the spatial variations in SOC fractions, and they can explain 74%, 65%, 51%, and 76% of the variation in SOC, ECO, MBC, and DOC, respectively. Furthermore, the latitudinal patterns for the SOC fractions were mainly controlled by climate, with soil texture as the sub–dominant factor for SOC and EOC, and soil microbe and vegetation biomass as the sub–dominant factors for MBC and DOC, respectively. Forestsoil humic carbon HAC, FAC, HUC, and HEC contents were 23.12 –77.00 g kg–1, 0.44–1.62 g kg–1, 7.80 –18.30 g kg–1, 11.37–49.98 g kg–1 and 8.53–19.94 g kg–1, respectively. 2. HAC, FAC, HUC, and HEC in forest soils increased exponentially with increasing latitude(P < 0.001), representing a general trend of tropical < subtropical < temperate. The ratios of humic carbon fractions to SOC were 9.48–12.27%(HAC), 20.68–29.31%(FAC), and 59.37–61.38(HUC). Climate, soil texture and soil microbe jointly explained more than 90% latitudinal variation of SOC, HAC, FAC, HEC, and HUC, and the interactive effects were more important. These findings fill the gaps of latitudinal pattern for soil carbon fractions in forest at large scale, and may help us to develop or improve the models of soil carbon turnover and storage.