Effects of different vegetation on autotrophic carbon fixation capacity and autotrophic microbial community in karst soil

The process of autotrophic carbon fixation can make considerable contribution to soil organic matter (SOM). However, the effects of different vegetation on the capacity of autotrophic carbon fixation and the autotrophic microbial community were not clear. In this study, we used 13C (13CO2) isotope labelling combing cross-polarization with magic angle spinning (CP-MAS) 13C nuclear magnetic resonance (NMR) and metagenomics to investigate the autotrophic carbon fixation capacity and autotrophs community of four typical soils (Alfalfa field, shrubland, cornfield and bare land) in a control karst experiment site. The 13C-NMR analysis showed that the 13CO2 was incorporated into the different chemical categories in SOM. The vital autotrophs mostly belong to Actinobacteria, and ammonia oxidizer play an important role. These results showed that the photoautotrophy was the primary in topsoil, while the chemolithoautotrophy plays an important role in carbon cycle of karst soil. Meanwhile we provided direct evidence of autotrophic inorganic carbon fixation with 13C-NMR and statistical evidence of autotrophic microbe community in karst different land-use soils.自养碳固定（autotrophic carbon fixation）过程对土壤有机质（soil organic matter, SOM）具有显著贡献。然而，不同植被对自养碳固定能力及自养微生物群落的影响尚不明确。本研究采用13C（13CO2）同位素标记结合交叉极化-魔角旋转（cross-polarization with magic angle spinning, CP-MAS）13C核磁共振（nuclear magnetic resonance, NMR）与宏基因组学（metagenomics）技术，对喀斯特对照试验样地中4种典型土壤（苜蓿田、灌丛地、玉米田与裸地）的自养碳固定能力与自养微生物群落展开研究。13C-NMR分析结果显示，13CO2被整合至SOM的不同化学组分中。关键自养微生物主要隶属于放线菌门（Actinobacteria），且氨氧化微生物发挥着重要作用。研究结果表明，表层土壤以光能自养作用（photoautotrophy）为主，而化能自养作用（chemolithoautotrophy）在喀斯特土壤碳循环中占据重要地位。本研究同时通过13C-NMR为喀斯特不同土地利用方式下的土壤自养无机碳固定提供了直接证据，并为自养微生物群落提供了统计学支撑。