持续扰动下农田SOM固持及微生物学机制

Continuous disturbance is one of sufficient and necessary conditions for microbial-mediated soil organic matter (SOM) formation. We want to investigate whether the environmental disturbances can promote SOM sequestration. The microcosm incubation will be set up under constraints of repeated synthetic nitrogen addition with different frequency and continuously varying temperatures. The 13C-labeled corn stalk and root are used as exogenous organic residues, which being applied to black soil and aquatic brown soil, respectively. In order to reveal the temporal dynamics of recalcitrant vs. labile C pools, microbial community structure and ecology strategies, we will use stable isotopic probing technique to differentiate and measure the residue- and SOM-derived C flux, soluble organic C and lignin, microbial biomarkers like phospholipid fatty acid and amino sugar, and fungal and bacterial diversity and composition through high-throughput sequencing. Enzyme activities related to different organic C compounds decomposition are also detected. Through multivariate analysis, we will rationalize the co-metabolism of exogenous residue- and extant SOM-derived C compounds and their relationship with related microbial ecology strategies, composition and activities. This proposal will address the knowledge of responding realistic and effective ecological functions of microbiome involving in the key metabolic pathway of SOM accumulation by residue quality control and synthetic nitrogen addition in the agroecosystem of northern China.

持续扰动是土壤有机质（SOM）形成充要条件之一。针对植物残体添加条件下农田SOM养分固持对施氮与温度扰动反馈机制的科学问题，提出通过分析不同质量13C标记外源有机残体与内源SOM的碳组分和微生物组协同代谢特征，可明确施氮和温度扰动促进SOM对外源碳组分固持的微生物学机理。项目拟选取13C标记茎叶和根系为外源有机底物，以黑土和潮棕壤为供试土样，设立氮肥高-低施用频次和循环变温-恒温相对照的室内控制实验。采用同位素示踪技术，检测分别来自13C标记植物残体和SOM的碳矿化速率，易分解（水溶性碳）和难分解（木质素）组分及微生物标识物（磷脂脂肪酸、氨基糖）含量；结合高通量测序技术，分析SOM和植物残体来源的真（细）菌丰度、组成、多样性和科属分类特征。同时，检测与有机残体分解相关的主要胞外水解酶活力。研究旨在揭示秸秆还田条件下氮肥精准投放对农田SOM养分固持影响的微生物机制及相关生态过程的温度敏感性。

针对不同质量植物残体添加条件下农田SOM养分固持对施氮、温度、耕作等环境因素扰动对特定碳组分矿化过程及相关菌群组成及多样性影响及其反馈机制的科学问题，提出利用多因素多水平室内微域培养，分析不同质量13C标记外源有机残体与内源SOM的碳组分和微生物组协同代谢特征，可明确特定环境因子扰动利于SOM对外源碳组分固持的微生物学机理。项目分别选取13C标记籽实、茎叶和根系为外源有机底物，并额外施加木质纤维素不同残体质量物影响，以黑土和潮棕壤为供试土样并辅以不同干扰程度农田耕作土壤，并设立氮肥高-低施用频次和循环变温-恒温相对照的室内控制实验，测定不同处理土壤碳矿化速率、碳氮循环相关酶活力、真（细）菌微生物群落时序特征，明确局限条件下SOC矿化对不同生态因子的响应规律。通过对不同培养时期主要微生物群落活体生物量累积积分，明确各主要菌群累积生长力及其对土壤碳矿化和土壤有机质积累贡献力及其对外界因素干扰、残体质量响应规律。结果表明，不同培养时期土壤瞬时呼吸速率、碳矿化过程动力学参数、水溶性碳、磷脂脂肪酸与氨基糖、真（细）菌群多样性等指标均温度、氮素和耕作等因素扰动的显著影响。总体上，不同有机碳库矿化速率、碳氮循环相关酶活力、土壤微生物多样性，随温度变化呈现变温处理显著高于恒温处理，高质量外源残体明显高于低质最残体处理，多氮频次显著高于单一氮频次处理。此外，恒温处理条件下的碳矿化、水溶性碳和微生物群落温度敏感性变化远低于变温处理，应对环境扰动，微生物群落明显进化出更快生长速率和适应策略。外源植物质量显著地影响了植物源微生物群落生长，依次是籽实最大，叶片次之，根系最小；革兰氏阴性细菌变化最为明显，残体质量效应几乎不受其它因素影响；非扰动土壤显著高于扰动处理（除革兰氏阴性细菌）；革兰氏阳（阴）性细菌累积生长力远大于真菌，而放线菌累积生长力最低。研究揭示秸秆还田条件氮肥精准投放对农田SOM固持影响的微生物机制及相关生态过程。