有机培肥下红壤团聚体中食细菌线虫捕食对解磷微生物多样性及其功能的作用机制

Red soil is the low yield soil which distributes widely in hilly and mountainous region of southeastern China. The acidification of red soil causes low level of fertility and serious deficiency in phosphorus pool. The diversity of phosphate-solubilizing bacteria closely related to efficient conversion of phosphorus. In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new genotypes or phenotypes. The rapid diversification characteristic of adaptive radiation is thought to be driven by strong divergent natural selection generated through resource competition and predation. The impact of bacterivorous nematodes predation on the extent and rate of diversification in microorganisms remains unclear. Based on ecological network analysis, we have evaluated the influence of nematode-microorganism interactions on microbial community composition and functions in red soils under the long-term manure experiment. The community structure of phosphate-solubilizing bacteria in the bacterivorous nematode guts is analyzed to determine the selective feeding habits of nematodes on phosphate-solubilizing bacteria. The spatiotemporal characteristics of phosphate-solubilizing bacterial diversification in aggregate fractions are investigated to reveal the time and space "synchronization" effects of nematode selective predation on the succession of phosphate-solubilizing bacterial diversity, and to clarify the mechanisms of nematodes-microorganisms interaction on phosphate-solubilizing bacterial diversification and evolution rate. The molecular mechanism of dominant bacterivorous nematodes (Protorhabditis) grazing on the diversification (mutation rate) of the model strain is further tested in experimental microcosms under strictly controlled laboratorial conditions. Consequently, this project will enrich the knowledge of phosphate-solubilizing bacterial diversification in adaptive radiation, succession rate and function in red soils, and provide a theoretical basis for synchronized improving soil fertility and functional microbial diversity and building healthy ecological effects of red soils.

红壤是我国东南丘陵区广泛分布的中低产土壤，红壤酸化导致肥力水平低，有效磷库严重亏缺。红壤解磷微生物多样性与磷素高效转化功能密切相关。资源竞争和生物捕食驱动了生物多样性的适应辐射现象，但土壤食细菌线虫的捕食作用对解磷微生物多样性及其功能的影响尚不明确。本项目针对红壤旱地农田生态系统，基于长期施用有机肥试验结果的网络模型分析，在明确线虫—微生物互作对红壤微生物群落结构和功能活性影响的背景下，研究食细菌线虫肠道内解磷微生物的群落结构特征，剖析食细菌线虫对解磷微生物选择性捕食规律；围绕土壤团聚体揭示解磷微生物多样性演变的时空特征，从微观角度解析线虫选择性捕食对解磷微生物多样性变化的时空“同步”效应，阐明线虫—微生物互作对解磷微生物多样性形成、演变速率及代谢功能的驱动机制；结合室内土壤微域实验，从分子水平（基因突变率）揭示红壤优势食细菌线虫（原杆属）对模式菌株荧光假单胞菌SBW25多样性的作用机制。

红壤是我国东南丘陵区广泛分布的中低产土壤，红壤酸化导致肥力水平低，有效磷库严重亏缺。红壤解磷微生物多样性与磷素高效转化功能密切相关，但土壤食细菌线虫的捕食作用对解磷微生物多样性及其功能的影响尚不明确。本项目针对红壤旱地农田生态系统，基于有机培肥长期试验，（1）研究了红壤团聚体中线虫—微生物互作对碳转化的调控机制。高肥处理下大团聚体中>100μm的大孔隙数量显著增加，为食细菌线虫提供了生活更为适宜的空间，其优势类群原杆属的丰度最高。与小团聚体相比，大团聚体中高丰度的食细菌线虫促进形成了高度复杂的线虫—细菌网络结构，食细菌线虫的捕食作用通过增加细菌与真菌比值（B/F）促进了土壤有机碳库容与周转速率的增加。（2）揭示了土壤微食物网中真菌途径对根际磷转化和植物生产力的促进机制。施用有机肥下食真菌原生动物和线虫的捕食作用刺激AMF生物量增加，显著改变了AMF群落组成。高肥处理下，食真菌线虫优势属滑刃属和真滑刃属肠道中AMF丰度更高，提示两种优势食真菌线虫对AMF的取食效应更强。AMF-食真菌动物的相互作用增加了AMF在玉米根部定殖以及植物中P转运蛋白基因ZMPht1;6的表达水平，提高了植物生产力。（3）揭示了生物炭负激发效应的关键微生物竞争作用机制。生物炭施用影响了土壤细菌和真菌群落的组成和共生网络关系；生物炭施用导致细菌和真菌网络中关键类群的竞争性交互作用增强。通过结构方程模型分析表明，网络关键种与其他微生物间的竞争性交互作用提高了细菌和真菌多样性，降低了碳水化合物分解代谢活性和土壤呼吸熵。施用生物炭后细菌网络关键物种变为节杆菌属和芽单胞菌科属，真菌网络关键物种变为毛壳霉属和青霉属，施用生物碳促进了这些关键物种与其他微生物之间的竞争作用，导致生物炭的负激发效应。本项目为解析红壤肥力与功能微生物多样性协同提升机制，构建良好的红壤生态效应提供理论依据。