农田土壤中木质素的降解特征及其微生物驱动机制

Straw mulching is one of the main methods to sequester carbon in agricultural soils. Lignin is the main component in straw; hence, lignin degradation affects the size and stability of the carbon pool in agricultural soils. Microorganisms play a crucial role in lignin degradation, and microbial communities and enzymatic activities are closely related to the process of lignin degradation. In this study, field surveys will be carried out to elucidate the characteristics and structure of lignin in typical subtropical agricultural soils of China. In situ observation of long-term experiments is conducted to study dynamic changes in the relative rate, structure, and enzymatic activity of lignin degradation in several typical agricultural soils. We attempt to reveal dynamic changes in the quantities and communities of microbial functional groups in terms of fungal communities and functional gene diversity in the process of lignin degradation. Multivariate statistical methods are used to analyze the relationships between lignin degradation and changes in microbial functional groups. The objective of this investigation is to determine the content, structure, and degradation characteristics of lignin, as well as the microbial mechanisms that drive lignin degradation in different subtropical agricultural soils. The results of this study are expected to provide a scientific basis for understanding the microbial mechanisms of soil organic carbon stability in agricultural soils.

秸秆还田是主要的农田土壤固碳措施之一。木质素作为秸秆的主要组分之一，其在土壤中的降解直接影响农田土壤碳库的大小和稳定性。微生物作为土壤中木质素降解的主要驱动力，其群落结构和酶活性与木质素的降解过程密切相关。本项目拟通过区域调研结合长期定位试验原位观测，明确我国亚热带典型农田土壤中木质素的含量和结构特征，观测秸秆还田措施下几种典型农田土壤中木质素的相对降解速率、结构（各单体的含量和比例）与相关酶活性的动态变化，并从降解木质素的真菌群落结构和功能基因多样性方面，研究木质素降解过程中活性功能微生物数量和群落的动态变化，采用多元统计方法，分析并比较不同农田土壤中木质素的降解与微生物功能群数量和群落动态变化的内在关系。研究结果将阐明亚热带典型农田土壤中木质素的含量、结构、降解特征及其降解的微生物驱动机制，为加深理解农田土壤有机碳稳定性的微生物学机理提供科学依据。

秸秆还田是维持和增加农田土壤有机质的重要管理措施，而木质素作为农作物秸秆的重要组分之一，其积累转化特征影响土壤有机碳的周转速率和碳库的大小。项目采用长期定位试验与田间原位培养试验相结合的手段，观测秸秆配施化肥及单施化肥对亚热带红壤旱地、红壤水旱轮作地、石灰土旱地中木质素的动态变化，并分析不同农田土壤中木质素的积累与微生物功能群动态变化的内在关系，阐明木质素的积累特性和微生物耦合机制。结果表明：长期秸秆还田配施化肥有利于亚热带农田土壤中木质素的积累，红壤旱地、红壤水旱轮作地及石灰土旱地的总量分别于长期定位试验前414.47、201.56、337.12 μg∙kg-1 增至 2092.40、1972.24、2096.52 μg∙kg-1；与定位试验前相比，不同土地利用方式下木质素的积累具有单体特异性，红壤中木质素组分C类单体显著积累、石灰土则表现为V类单体比例显著增加；周年动态变化来看，一年内木质素的绝对含量及其对有机质相对贡献的增幅并不明显；含漆酶基因的细菌群落对漆酶（降解木质素关键酶）活性贡献较大，可解释其>90%的变异，且细菌丰度与漆酶活性线性关系显著，表明含漆酶基因的细菌群落（cbr1-cbr2）可能是指征亚热带农田土壤中木质素积累的关键功能微生物；氮素是驱动三种土壤中木质素积累的显著因子；结构方程模型表明，含漆酶基因的细菌群落组成对土壤中木质素的积累存在直接或间接影响。