基于生态化学计量学研究典型旱地土壤有机碳转化与演变过程

In the intensively managed agro-ecosystem, inputs of organic amendments and nitrogen (N), phosphorus (P) nutrients is the most direct and efficient practices to enhance soil carbon sequestration and improve soil fertility. Changes in soil nutrients availability and the stoichiometric ratios (C:N:P) resulted from long-term fertilizer and organic amendments regime may act on soil organic carbon (C) turnover process and evolution by altering soil microbial community and structure. However, the mechanism of this process is still unknown. Based on typical long-term fertilization experiment net and ecological stoichiometry theory, we aim to explore the characteristic, regulation coefficient, and regulating factors of C, N, P stoichiometry in soil-aggregates-microbial biomass in typical upland. Combined techniques of labeled isotope and molecular biology with 13C-PLFA-SIP would be used to study the dynamic of stoichiometry, microbiology biodiversity, and extracellular enzyme in soil organic C turnover process under various soil C, N, P availability gradient and limited nutrients addition. This incubation experiment is designed to illustrate the response of community and biodiversity of key functional microbes involved in added carbon source to changes in soil N and P nutrients. Multivariate statistics techniques and structural equation model (SEM) will be implied to quantify the interaction influence of C, N, P stoichiometry of soil, aggregates, and soil microbes on soil organic C turnover process. The objective is to reveal the co-driving mechanism of C, N and P stoichiometry combined with key functional soil microbes on soil organic C turnover and evolution under long-term nutrient input. Results from this project are supposed to enrich better understanding of elements interactions under intensive nutrients managements, and provide scientific foundation for sustainable nutrients management.

集约化管理下农田氮磷养分和有机物输入是增加土壤固碳，提升土壤肥力最直接有效的方式。这种长期、重复输入导致的碳氮磷有效性及计量比差异，可能通过改变微生物群落结构而作用于土壤有机碳转化过程，但其机制尚不清楚。本研究依托典型旱地长期试验，基于生态化学计量学原理，研究典型农田土壤-团聚体-微生物碳氮磷化学计量特征、内稳性指数及其主控因子。采用同位素示踪、分子生物学及同位素探针等技术手段，研究不同氮磷梯度及限制性氮或磷养分添加条件下，土壤微生物碳氮磷计量比、群落结构及胞外酶动态，阐明参与外源碳转化过程关键功能微生物群落多样性及其对氮磷变化的响应过程；通过多元统计分析和结构方程模型，明确土壤氮磷有效性及计量比对有机碳转化的影响及其程度，揭示施肥条件下土壤碳氮磷化学计量特征与关键功能微生物驱动有机碳转化与演变的联动机制。研究结果将丰富集约化管理农田土壤碳氮磷元素互作理论，为土壤养分的可持续管理提供依据。

集约化管理下长期、重复的养分输入会改变农田土壤碳氮磷有效性及计量比，通过影响微生物群落结构和酶活性进而导致土壤碳氮转化过程变化，但其影响机制尚不清晰。项目依托3种典型土壤（黑土、潮土和红壤）长期施肥定位试验，结合同位素示踪和微生物分子生物学方法，研究了长期施肥下土壤碳氮磷（C、N、P）化学计量比变化特征及其对土壤有机碳转化过程的作用机制。结果表明，土壤与微生物的CNP化学计量比受到施肥和土壤类型共同影响。相对于单施化肥，有机物料投入对于黑土和潮土主要通过降低微生物量碳（SMBC）与氮（SMBN）计量比形成较高的土壤碳氮失衡（C:N imbalance），但在红壤上通过提高SMBC: SMBN造成较低的C:N imbalance。内稳性模型结果显示，施肥管理下农田土壤微生物群落不具有保持其自身化学元素组成相对稳定的能力。与化肥相比，有机肥的投入显著增加了黑土表层土壤真菌细菌比，土壤pH和碳氮磷的失衡（imbalance）是驱动微生物群落结构改变的关键因素，也是土壤碳和氮矿化速率的控制因子，与碳氮磷有效性的计量比（与DOC: Mineral N、DOC: Available P、Mineral N: Available P）一起控制微生物碳氮利用效率（CUE, NUE）及激发效应强度。碳源的重复添加引起的激发效应强度随土壤肥力水平和氮素有效性的增加而降低，具有明显的“马太效应”。结合高通量测序分析发现，养分有效性及其计量比主要是通过改变细菌物种Chloroflexi和Planctomycetes相对丰度进而影响有机碳的矿化强度。养分添加会显著提高低肥力潮土有机碳矿化，不添加或者同时添加氮磷养分显著提高了低肥力潮土激发效应强度。这些结果证实了施肥管理措施主要是改变土壤碳氮磷化学计量比以及pH来调控微生物群落组成，通过控制底物碳氮磷的有效性及微生物碳氮利用效率进而控制土壤本底碳矿化和外源碳固存，揭示了碳氮磷化学计量驱动土壤有机碳转化与演变的过程机制，相关成果发表在《Soil Biology and Biochemistry》、《Biology and Fertility of Soils》、《Applied Soil Ecology》等国内外知名期刊发表论文12篇。研究结果丰富和完善了土壤碳氮磷元素互作理论，可为农田土壤碳氮的可持续管理提供理论支撑。