Variations Of Soil Labile Organic Carbon In The Poplar Plantations Of Different Ages In A Coastal Area Of Northern Jiangsu

The dynamics of soil organic carbon is a hot issue in the current climate change research.To understand the variations of soil labile organic carbon and their correlations with soilphysical and chemical properties, the poplar plantations (Populus euramericana San Martino)at five age levels (i.e.4,8,12,15, and20years old) were selected as study sites in a coastalarea of northern Jiangsu province. An experiment was conducted to analyze the soil totalorganic carbon (TOC), water-soluble organic carbon (WSOC), microbial biomass carbon(MBC), soil physical and chemical properties of the0-10,10-25,25-40cm soil layer. Theresults showed that：(1)The soil TOC, WSOC, MBC in all plantations decreased with soil depth increasing.The soil TOC increased with the plantations'age under15years old, and then appeared a stabletrend. The maximum of TOC was in the plantation at15years old, and the minimum was at4years old. Soil WSOC and MBC had the same variation trend as soil TOC. TheWSOC/TOC and MBC/TOC ratios increased with the plantations'age increasing. The WSOCwas significantly correlated with the MBC. Furthermore, the WSOC and MBC weresignificantly related to TOC, TN, C/N, pH, soil bulk density, respectively.(2)The season changes of TOC in all poplar plantation VIwas not obvious. The WSOCand MBC were higher in spring and summer, but lower in autumn and winter at all poplarplantations, especially in the0–10cm soil layer. The maximum of WSOC was in spring, andthe minimum was in the fall. The maximum of MBC was in summer, and the minimum wasin the autumn or winter. The WSOC was significant correlation with the MBC. However,the WSOC and MBC were not significantly related to soil temperature and soil moisture.(3) In all, the soil TOC increased with the plantations' age under15years old, and thenappeared a stable trend. Soil WSOC and MBC had the same variation trend as soil TOC. TheWSOC and MBC were higher in spring and summer, but lower in autumn and winter at allpoplar plantations. The seasonal variation of WSOC and MBC is not only associated with soiltemperature and soil moisture, but also the soil physical and chemical properties, seasonalchanges of ground cover. The changes of ages and seasons may have a significant impact onsoil the content and stability of soil labile organic carbon. We might change the heat and waterfactors, nutrient factors and soil structure to increase the soil carbon sink and its stability.