红壤丘陵区旱地和水旱轮作地土壤中纤维素降解功能微生物群落特征

Characteristics of cellulose-degrading microbial communities in upland and paddy-upland rotation land soils in red soil hilly region

为揭示农田土壤有机质中纤维素降解的微生物机制,依托红壤丘陵区长期定位试验,以两种土地利用方式(旱地和水旱轮作地)下两种施肥模式(化肥、秸秆还田配施化肥)的农田生态系统为研究对象,分析了表层土壤中纤维素含量、纤维二糖水解酶活性以及纤维素降解功能微生物丰度与群落结构的周年动态变化特征。结果表明:长期(13年)施肥后土壤中纤维素并未发生显著积累,且从周年动态变化来看,秸秆还田后旱地和水旱轮作地中纤维素分别在6个月和3个月内完全降解或被转化为其他形态;相关分析表明,纤维二糖水解酶活性与纤维素含量呈显著正相关,而真菌cbh I基因丰度与纤维二糖水解酶呈显著正相关(P<0.01),因此功能基因cbh I可用于指示本研究供试土壤中降解纤维素的关键微生物群;聚类分析表明,旱地和水旱轮作地的纤维素降解微生物(含cbh I基因)互相分离,即与施肥相比,土地利用方式是引起土壤中纤维素降解微生物群落组成改变最主要的因素;克隆测序结果显示,两种土地利用方式下纤维素降解功能微生物均以伞菌和粪壳菌占绝对优势,分别占总克隆库的22.9%~39.5%(平均为34.7%)和17.7%~42.3%(平均为28.5%),其中秸秆还田后的纤维素降解过程可能由粪壳菌主导。研究结果阐明了红壤丘陵区旱地和水旱轮作地中秸秆还田后纤维素降解及其功能微生物群落的异同,为揭示农田土壤新鲜有机质中易分解组分(纤维素)的微生物转化机制提供了基础数据。

Cellulose is the most abundant organic component in crop residue and thus plays a vital role in organic matter transformation in agricultural soils. The degradation of cellulose in soil is mainly driven by microorganisms. The fungal cbh I gene is one of the key microbial genes participating in cellulose degradation. Based on long-term field experiments in subtropical hilly region, two land use types（upland and paddy-upland rotation land） and two fertilization treatments（chemical fertilizers and chemical fertilizers combined with crop straw）were selected for this study. The annual dynamics of cellulose content, cellobiohydrolase activity, and abundance and composition of cellulose-degrading microbial communities containing cbh I in surface soils were analyzed to reveal the characteristics of microbial decomposition of cellulose in agricultural soils. Results showed that after 13 years of long-term fertilization, cellulose had not accumulated significantly.Annual dynamic data indicated the newly added cellulose was degraded or converted into other forms within 6 and 3 months after straw incorporation into upland and paddy-upland rotation land soils, respectively. Both the Pearson correlation analysis and stepwise linear regression analysis showed that cellulose contents were positively related to the activity of cellobiohydrolase and that abundances of the fungal cbh I gene were positively related to cellobiohydrolase activity（P0.01）. This indicated that the fungal cbh I gene may be a potentially corresponding indicator of microbial decomposition of cellulose in the tested agricultural soils. Cluster analysis showed that cellulose-degrading microbial communities in upland soils and paddy-upland rotation land soils were separated from each other, suggesting that land-use type is the key factor in shaping cellulose-degrading microbial communities as compared with the fertilization treatments. Cloning and sequencing data showed that Agaricomycetes and Sordariomycetes, which accounted for 22.9% ~39.5%（average 34.7%） and 17.7% ~42.3%（average28.5%）of total clones, respectively, were the dominant cellulolytic microbial groups. Sordariomycetes may dominate the microbial process of cellulose decomposition after crop straw returns to the field. This study clarified the similarities and differences of cellulose decomposition and its functional microbial communities between upland and paddy-upland rotation land after straw returns to the field, and thus provided the basic data on revealing microbial mechanisms of labile soil organic matter（cellulose）turnover in agricultural soils.