亚热带红壤区森林土壤剖面微生物残体碳分布及影响因素

Abstract

土壤剖面中20cm以下土壤有机碳（SOC）储量占土壤剖面总SOC储量50%左右，由于土壤微生物残体碳（MRC）是稳定土壤碳库的重要来源，因此研究土壤剖面中MRC对SOC的贡献对于评估土壤碳储量具有重要意义。然而，目前关于MRC含量及其对SOC贡献的研究多数集中在土壤表层，在土壤剖面和母质中尚不清楚。选取江西省千烟洲亚热带典型森林红壤剖面，通过氨基糖与磷脂脂肪酸（PLFA）微生物标志物分析方法，分析红壤剖面和母质中MRC的影响机制及其对SOC贡献的分布特征。研究结果表明：（1）MRC含量随着土壤剖面深度增加而显著降低（P<0.05），在整个土壤剖面中，细菌MRC对SOC贡献为6%-12%，真菌MRC对SOC贡献为12%-36%，MRC对SOC贡献为18%-46%。从土壤表层至母质，真菌MRC对SOC贡献高于细菌MRC。（2）结构方程模型结果表明，在土壤剖面中，MRC含量主要受到微生物-PLFA含量、容重和溶解态有机碳含量的影响。研究量化了红壤剖面中MRC对SOC的贡献，表明在20cm以下土壤及母质中，微生物残体碳对红壤地区生态系统碳库具有重要贡献。;In soil profiles, soil organic carbon (SOC) storage beneath 20cm accounts for about 50% of the total SOC storage in the terrestrial ecosystem. Microbial residue carbon (MRC) is considered as an important constituent of persistent soil organic carbon. It is important to learn the role of MRC for soil carbon storage in deep soil as the main source of soil stable carbon pool. Until now, most studies involving MRC content and the contribution of MRC to SOC have mainly focused on surface soil, but seldom in deep soil and parent material. In this study, we selected typical red soil profiles in Qianyanzhou, Jiangxi province in subtropical region. We measured the microbial biomarkers of amino sugars and phospholipid fatty acids (PLFAs) which represent microbial residue carbon content and living microbial biomass content, respectively. The objective of the study was to analyze the influence factors of MRC and to quantify the contributions of MRC to SOC along the soil profiles from the surface to parent material. The results showed that (1) bacterial residue carbon (MRC_B), fungal residue carbon (MRC_F) and MRC contents decreased significantly with soil depth (P<0.05), and were about 0.08, 0.18, 0.25 g/kg at the parent material, respectively. The contributions of MRC to SOC along the soil profiles remained unchanged because of the same variation trend of MRC and SOC contents. Along the whole soil profiles, the contributions of MRC_B, MRC_F and MRC to SOC were about 6%-12%, 12%-36% and 18%-46%, respectively. The contribution of MRC_F to SOC was higher than that of MRC_B to SOC from surface soil to parent material. This may be caused by different components of cell walls in bacteria and fungi. The chitin in cell wall of fungi is more difficult to decompose than peptidoglycan in cell wall of bacteria. In addition, MRC_F could have more physical protection than MRC_B by soil aggregates since extracellular mycelia and polysaccharides are involved in the formation of soil aggregates. (2) The structural equation model showed that MRC content was largely determined by microbial biomass content of PLFA biomarkers, soil bulk density (Db) and dissolved organic carbon (DOC) content in the soil profiles, while Db and DOC indirectly influenced but microbial-PLFA content directly influenced the MRC content. Our study quantified the contribution of MRC to SOC along the soil profile and emphasized the contribution of MRC to the formation of ecosystem carbon pool beneath 20cm and in the parent material in red soil region.