农田土壤微生物多样性形成规律的热能理论研究

The mechanism of microbial diversity formation is one of the most important scientific topics currently. The metabolic theory of ecology (MTE) emphasizes that the kinetic energy is the deterministic driving factor of the species diversity: higher temperature causes faster cell metabolism rate and higher gene mutation rates, resulting a more diverse community. Ln (species richness) is negatively correlate to the reciprocal absolute temperature. Nowadays, it is still not clear whether the MTE hypothesis in macro-ecology can be applied to microorganisms. This project intends to analyze the influence of temperature on the bacterial diversity at both molecular and community levels. The diversity of model microbial strains, simulated bacterial community and soil microbial communities across temperature gradient and environmental condition gradient in will be studied systematically. In laboratory conditions, the mode strain of the fluorescent pseudomonad strains SBW25 and the simulated community of r- and k-type bacteria will be used to illuminate the adjustment effect of temperature on mutation rate related genes and directly demonstrate the influence of temperature on succession of bacterial diversity formation. In natural environment, the variation of soil microbial diversity along the temperature gradient will be studied, and bacterial diversity in typical types of soils with pH and organic matter content gradients in eastern China will be compared. The quantitative relationship between bacterial diversity and temperature will be validated and revised. This driving mechanism of soil biodiversity formation will provide a theoretical basis for the nutrient cycling regulation and soil fertility improvement in farmland.

微生物多样性形成理论是当代生态学研究的热点和难点。宏观生态学的代谢理论（MTE）认为温度决定了物种多样性分布，温度高导致细胞代谢速率和基因突变率升高，最终形成较高的物种多样性，物种丰富度的对数与绝对温度的倒数间呈线性关系。目前仍不清楚MTE假说是否适合微生物，以及是否需要修正。本项目拟在分子和群体两个水平上，针对模式菌株、模拟微生物群落以及不同土壤微生物群落，系统研究温度梯度和环境条件梯度对细菌多样性的影响规律。首先基于实验室模拟试验，针对荧光假单胞菌模式菌株SBW25以及r型和K型细菌的模拟群落，阐明温度、pH和碳源浓度梯度对基因突变率和细菌多样性的影响机制和定量关系；然后基于中亚热带到寒温带的土壤置换试验，研究具有pH和有机质含量梯度的典型土壤类型中微生物多样性沿热量梯度的变化规律，验证温度对细菌多样性的定量关系。本项目可为农田养分循环调控和地力提升提供理论依据。

生态代谢理论（MTE）提出温度增加提高细胞代谢速率和基因突变速率，形成较高的物种多样性。项目针对MTE假说是否适用微生物多样性形成以及是否需要修正的问题，以模式菌株和不同土壤微生物群落为对象，开展了室内模拟试验、土壤置换试验和区域调查，利用高通量测序、功能基因芯片和荟萃分析，研究了环境条件（温度、碳源、pH）和生物特征（微生物体型大小、功能生物间相互作用）对细菌多样性的影响规律和定量关系。.(1)针对荧光假单胞菌SBW25野生型（wild type）和突变型（△mutS和△mutL）菌株的模拟群落，发现温度（5～30℃）与pH（4.5～8.5）通过影响SBW25的突变速率和生长速率进而影响其多样性形成；温度和多样性MTE关系的斜率为-0.64～-0.72；温度和pH对MTE的修正模型为：lnD∝lnA-Eα/RT-ln(1+10^(pK-pH)))。(2)验证了温度、pH与土壤细菌多样性的关系模型，在区域尺度（中国），水稻土和旱地土壤中Boltzmann斜率关系分别为-0.03和-0.2，在全球尺度为-0.2。(3)基于东亚稻田和全球土壤的荟萃分析发现：不同生物体型（繁殖体）在0.2～1612微米，生物体型与丰富度、扩散速率和生态位宽度负相关；较小的生物（细菌）受环境过滤和扩散限制较弱，群落构建趋向随机性，生物多样性更大。(4)基于土壤置换试验（SRTE，2005～）中黑土南移试验（寒温带-暖温带-中亚热带）发现：水热条件增加显著降低黑土微生物的分类多样性及系统发育多样性，增加了微生物群落的演替速率，其中拟杆菌门、变形菌门和浮霉菌门对水热条件敏感；水热条件增加（特别是在中亚热带）显著增加黑土微生物之间的竞争关系（负连线比例），导致放线菌的枢纽作用下降，拟杆菌门和芽孢菌的枢纽作用增强；水热条件增加与施肥对黑土C、N转化功能基因产生激发效应。(5)基于SRTE的秸秆腐解试验（2008～2017）发现：气候变暖（南移）增加了秸秆腐解微生物群落的演替速率；碳源质量主要影响了真菌群落结构的演替速率，并与温度有交互关系；气候变暖增加了难分解底物（玉米秸秆）微生物分子生态网络中的竞争作用，加速网络关键物种的改变。.