植物-菌根真菌反馈驱动南亚热带森林演替的机制

Previous studies on plant community succession had mostly focused on abiotic factors and the characteristics of dominant plant species. Not until recently, had researchers realized the importance of plant-soil feedback in regulating plant community dynamics. Evidence showed that negative plant-pathogen feedback can drive plant community compositional changes, while our previous study suggested a role of positive plant-soil feedback in maintaining plant species diversity. The interactions between mycorrhizal fungi and plants are ubiquitous in natural ecosystems, where these interactions could be positive or negative depending on soil nutrient condition and host species characteristics. Despite the ubiquity of plant-mycorrhizal fungi associations, studies on the role of mycorrhizal fungi in forest succession are very limited. During the succession of subtropical forests, soil N often increases and soil P often decreases along the process, while the diversity of mycorrhizal fungi tends to increase. We hypothesize that the mycorrhiza dynamic due to variations in soil nutrient content along the successional stages may result in the differential interactions between mycorrhiza and early versus late successional plant species. These differential plant-mycorrhiza interactions may be an important driving force for forest succession. In this project, we plan to use 3-5 subtropical forests in China as study systems to explore the role of plant-mycorrhizal fungi feedback in forest succession, which is likely to provide new insights into how forest succession can be regulated not only through environmental changes and plant competitions, but also through plant-soil microbe interaction. This study, including both positive and negative plant-soil feedbacks, may also be a nice addition to the existing studies on plant community dynamics dominated by negative plant-soil feedbacks.

植物群落演替机制的研究一般集中在非生物环境和植物自身的特性方面。近期研究指出，植物-土壤病原菌负反馈是植物群落动态变化的重要驱动力，而我们前期也发现植物-土壤正反馈对维持群落的稳定也具有重要作用。菌根真菌与多数陆生植物都存在相互作用，这种作用可以是互利共生，也可以是寄生。然而，目前植物-菌根真菌反馈在森林群落演替中的作用研究仍非常匮乏。热带亚热带森林的演替进程普遍伴随N养分积累，P养分降低，而菌根真菌丰度增加的趋势。我们假设：南亚热带森林演替的土壤养分含量变化导致的菌根真菌群落变化可能导致不同演替阶段中优势植物与菌根真菌形成不同反馈作用，而这种植物-菌根真菌反馈差异可能是南亚热带森林演替的重要驱动力。本项目拟以3-5个南亚热带森林为研究对象，探讨植物-菌根真菌反馈在森林演替中的作用，完善以非生物环境因子和物种特性为主体的森林演替理论，并丰富以植物-土壤负反馈为主体的植物群落的动态变化机制。

随着植物-土壤反馈研究的深入，土壤微生物群落对植物群落的动态变化起到的作用日益受到重视。以往的研究主要集中在植物-土壤病原菌负反馈对植物群落动态变化的作用。然而，我们前期的研究发现，成熟稳定的植物群落表现出更强的植物-土壤正反馈作用，而这种正反馈作用产生的过程鲜有研究。在本项目中，我们以与植物互利共生的菌根真菌作为切入点，通过比较呈现不同演替阶段森林群落中优势植物和相应土壤微生物群落的特点，探究植物-土壤微生物正反馈在群落演替过程中的作用。结果表明：（1）演替中期优势植物通过减少早期优势植物与外生菌根真菌的结合以抑制早期优势植物的生长，却不对演替晚期优势植物的生长表现产生显著影响；（2）在南亚热带森林中，宿主植物起到直接驱动土壤菌根真菌群落演替的作用，土壤资源则通过影响群落的优势植物或者影响植物-外生菌根相互作用来间接影响菌根真菌群落；（3）菌根真菌群落对宿主植物产生依赖于土壤资源水平的反馈作用。 本项目首次证明了土壤菌根真菌在调控南亚热带森林演替进程中的潜在作用，并提出了土壤资源通过影响宿主植物从而间接驱动根系菌根真菌群落变化的潜在新范式。项目成果发展了森林演替的基础理论，丰富了植物-土壤微生物正反馈研究，并从土壤微生物修饰的角度为加速森林演替的实践提供了一种新思路。