不同类型菌根植物的抗病性与森林群落物种共存

Feedback with soil biota is thought to be an important determinant of tropical and subtropical forest diversity. While previous studies mostly focused on the negative density dependent effects driven by soil pathogens, the mutualistic symbiosis between mycorrhizal fungi and host trees which could result in positive feedbacks were believed to have disadvantage on species coexistence. As two major parts of (sub)tropical forest communities, arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees could coexist stably in a same community and both have high diversities. Mycorrhizal fungi could promote the resistance of host plants against soil pathogens, and a recent study found that the type of mycorrhizal association explained much of the variation in plant-soil feedbacks. However, we currently lack vital experimental evidence to test the differences among AM and ECM trees, which requires understanding how different types of mycorrhizas regulate plant-soil feedbacks. In this proposal, we will therefore determine the network of interactions among plants, soil pathogens and mycorrhizal fungi in the field, and show using manipulation experiments whether this is related to the strength of plant-soil feedbacks. This aim requires coupling a comprehensive and unique dataset of spatial analyses of plant diversity with new analyses of pathogenic and mycorrhizal fungal diversity in subtropical evergreen forests, and novel manipulation experiments. By combining the negative and positive effects of plant-soil feedbacks, this project will show us a more comprehensive investigation on the coexistence between ECM trees and AM trees. This will make a step change in our understanding of the role of soil microbes in niche separation and species coexistence in subtropical forests.

“植物-土壤反馈”作用是森林群落物种共存的重要驱动因子，但现有研究通常只关注了病原菌驱动的负密度制约效应，而认为菌根真菌不利于生物多样性的维持。丛枝菌根树种和外生菌根树种在热带亚热带森林中具有较高的物种多样性且能够稳定共存。菌根真菌通过提高寄主植物的抗病性进而改变密度制约效应的强度，但不同类型菌根真菌与病原菌相互作用的差异及其对寄主植物群落构建的影响尚未有实验研究。本项目中，我们提出菌根真菌驱动的植物抗病性差异与生态位分化假说，以亚热带常绿阔叶林为研究对象，采用野外调查、野外和室内盆栽实验相结合的方法，探讨外生菌根真菌和丛枝菌根真菌在提高寄主植物抗病性中的不同作用，并研究其如何驱动不同类型菌根植物在空间异质性条件下的种间生态位分化。本项目将“植物-土壤反馈”作用中的正负反馈机制相结合，探讨不同类型菌根植物的抗病性差异对多样性维持机制的影响，可进一步完善森林群落物种共存理论。

近年来，外生菌根真菌、丛枝菌根真菌和病原菌共同驱动森林群落物种共存受到广泛关注。针对植物-土壤反馈作用的方向和强度的不确定性，本项目提出菌根真菌驱动的植物抗病性差异与生态位分化假说：森林群落中，植物根系与菌根真菌的互利共生能够显著增强寄主植物对土壤病原菌侵染的抵抗能力，但不同类型的菌根真菌对提高寄主植物抗病性的程度和机制存在较大差异，从而改变了土壤病原菌介导的密度制约效应的方向和强度，促进了植物物种间的生态位分化和共存。本项目以南亚热带常绿阔叶林为研究对象，采用大型监测样地动态监测、野外和温室控制实验相结合的方法，揭示了森林林下土壤中菌根真菌组成的地下高速网络通过连接母树和同种幼苗，进而实现母树对幼苗生长存活和抗病性的显著促进作用；采用更全面的多样性测度指标（谱系多样性）和更独特的种间作用方式（“植物-土壤反馈作用”驱动的间接种间作用），为土壤微生物驱动的“生物多样性-生产力”关系的形成提供了机制上的解释。课题组出色完成了项目申报书中预设的发表4-6篇SCI论文的目标，分别在Nature Communications（被国际菌根协会评为十大杰出成果）、Science Advances、 Soil Biology and Biochemistry、Oecologia和Journal of Plant Ecology上发表文章。相关成果不仅完善了现有的生物多样性形成和维持的理论体系，还为生物多样性保护和亚热带森林的保育提供了重要的理论基础。