南方典型滨海湿地土壤微生物群落对海平面上升的响应机制

Sea level rise seriously threatens coastal wetland ecosystems in China. Mangroves and Spartina alterniflora salt marshes are typical coastal wetlands in southern China and play an important role in global climate change. Analyzing the assemblage process and co-occurrence network of soil microbial community can provide theoretical basis for predicting the response and feedback of ecosystem to environmental change. However, the effects of sea level rise on the assemblage process and co-occurrence network of soil microbial communities in typical coastal wetlands in southern China have not been reported. Based on the in-situ marsh organ with elevation gradient, soil samples of mangrove and S. alterniflora under different water level gradient will be collected. Soil bacteria, archaea and fungi community will be analyzed by high-throughput sequencing, quantitative real-time polymerase chain reaction (qPCR) and bioinformatics techniques. This study aims to investigate: (1) the response mechanism of soil microbial community composition and diversity to sea level rise; (2) the effects of sea level rise on the assemblage mechanism of soil microbial community; (3) the influences of sea level rise on the co-occurrence networks of soil microbial community. In addition, soil microbial community will be combined with plant functional traits and soil physical-chemical properties to elucidate the key factors that affecting soil microbial community, and to reveal the relationships between soil microbial community and plant growth, soil carbon and nitrogen pools. This study can provide theoretical basis for predicting the evolution process of coastal wetland ecosystems under the background of sea level rise.

海平面上升严重威胁着我国滨海湿地生态系统。红树林和互花米草生态系统是我国南方滨海湿地的典型代表，在全球气候变化中起着重要作用。解析土壤微生物群落构建机制和共存网络，可为预测生态系统对环境变化的响应和反馈提供理论依据。然而，海平面上升对南方典型滨海湿地土壤微生物群落构建机制和共存网络的影响还未见报道。本项目依托原位水位梯度平台，采集不同水位梯度下红树林和互花米草土壤，利用高通量测序、实时荧光定量PCR和生物信息学等技术分析土壤细菌、古菌和真菌，研究：（1）土壤微生物群落组成和多样性对海平面上升的响应机制；（2）海平面上升对土壤微生物群落构建机制的影响；（3）海平面上升对土壤微生物共存网络的影响。此外，结合植物功能性状和土壤理化性质，阐明影响土壤微生物群落的关键驱动因子，并解析土壤微生物群落与植物生长、土壤碳氮库之间的关系。本项目可为预测海平面上升背景下滨海湿地生态系统的演变过程提供理论依据。

海平面上升已是不争的事实，严重威胁滨海湿地生态系统生物多样性和功能。在全球气候变化加剧情景下，海平面上升速率及后果将愈演愈烈。然而，我们对土壤微生物群落如何响应由海平面上升引起的土壤淹水频率的增加仍知之甚少。本项目依托漳江口原位水位梯度平台，聚焦不同淹水频率下2种典型生境土壤：红树林（Kandelia obovata, KO）和互花米草（Spartina alterniflora, SA），利用高通量测序，解析土壤微生物多样性、群落构建机制和共存网络对淹水频率增加的响应。主要结论如下：（1）由海平面上升引起的土壤含水量增加是影响土壤细菌和古菌群落的最重要环境因素；（2）物种替换过程主导了土壤细菌和古菌群落β多样性的变异，且随着土壤含水量增加，物种替换的相对贡献随之增加；（3）确定性过程主导了土壤细菌群落构建过程，且随着土壤含水量的变化程度的增大，异质性选择过程的相对贡献随之增强。不同于细菌群落，古菌群落构建以随机性过程为主，且随机性过程的相对贡献随着土壤含水量的增加而增强；（4）共存网络分析表明，细菌和古菌群落对于淹水频率增加具有不同的响应模式，即淹水频率增加显著降低了细菌网络复杂性，反之，增加了古菌网络复杂度；（5）与丰富种（AT）相比，稀有种（RT）的群落周转速率较低，生态位宽度更窄，在不同的环境梯度上表现出更强的系统发育信号，从而表现出更强的生态偏好；（6）群落构建分析表明，RT在系统发育上更趋于群落聚集，主要受匀质性选择主导，而AT则更倾向于群落分散，受扩散限制的支配，而土壤含水量的增加降低了AT和RT群落系统发育聚集程度；（7）结构方程模型分析发现，在不同淹水频率下，RT群落变异与红树林秋茄幼苗的生物量息息相关。总体而言，本项目初步解析了土壤微生物群落对淹水频率变化的响应规律，研究结果对于我们认识全球变化背景下滨海湿地土壤微生物多样性及其生态功能的演变具有重要意义。