植物-土壤反馈与草地群落演替:菌根真菌和土壤病原菌的调控作用

Abstract

由植物引起的根际土壤生物或非生物环境的改变能够反馈影响群落中不同植物的生长，直接改变共存植物的相对竞争关系，推动群落结构的动态变化。作为土壤生物群落的重要组成部分，土壤微生物在植物-土壤反馈关系中起到重要的调控作用，对解释植物群落的演替进程和方向有着重要的意义。在草地植物群落演替的早期阶段和外来物种入侵的过程中，宿主植物对丛枝菌根真菌（AMF）的依赖性较低，受本地病原菌的影响较小，一般不存在负反馈。在演替后期，植物对AMF更具依赖性，而积累的病原菌则产生较强的负反馈效应，从而促进群落物种共存和植物多样性，提高草地生产力和稳定性。研究微生物-植物反馈机制不仅有助于完善草地退化与恢复理论，还对退化草地恢复治理的实践有着指导意义。未来关于根际微生物-植物反馈在草地群落演替中的作用应该加强以下几方面的研究：（1）在实验方法上，开展专性微生物-植物反馈研究；（2）在测定指标上，进一步量化不同微生物在反馈关系中的功能差异；（3）在研究对象上，加强土壤微生物在植物群落水平的反馈研究；（4）在应用上，明晰植物-土壤反馈在退化草地恢复过程中的作用，指导草地管理实践。;Biotic and abiotic changes of soil properties (e.g. physical, chemical and biotic) caused by a plant affect the growth of other plant species within the same communities, reshape the competitive relationship between different species, and restructure the dynamic changes of species composition. The feedback between plant and soil has become an important concept for explaining the diversity, stability, dynamics and succession of plant communities. Its process and mechanism are also key scientific issues to understand the responses of terrestrial ecosystems to global changes. However, biotic factors, in particular soil microbes mediated plant-soil feedback are still poorly understood. These changes in key microbial groups, such as arbuscular mycorrhizal fungi (AMF) and soil pathogens may increase or decrease the plant growth, resulting in positive or negative plant-soil feedbacks. In the early successional stage or during exotic plant invasion, host plants preferentially utilizing abundant soil nutrients have low dependence on the AMF and are less affected by native pathogens. Generally, there is no negative feedback. In the late successional stage, as the nutrients are being depleted, AMF help host plants with better access to soil nutrients and increased resistance to stress and pathogens, which could generate positive feedback and potentially accelerate succession. However, the accumulated pathogens can generate negative feedback and contribute to plant species coexistence and diversity, and thus improved productivity and stability of grassland. The study of microbial feedbacks on plant community dynamic is not only helpful to improve the theory of grassland degradation and restoration, but also instructive to the practice of restoration and management of degraded grassland. In the future, the key issues of plant-microbe feedback in grassland community succession were suggested as follows. (1)In experimental methods, it is necessary to test the net effect of obligate microbes dynamics on the plant succession using a fully reciprocal inoculation experiment which involves host-mediated differentiation of microbial communities and differential effects of the microbes on the plant fitness. (2)Regarding measurement indexes, further work quantizing the trade-off between the nutrient uptake and the carbon allocated to the microbes by host plant is needed. Comparing the ratios of nutrient benefit versus carbon cost between plants reciprocally inoculated with own and foreign microbial communities would enable us to evaluate functional variation between different microbes. (3)For research objects, the impacts of microbes on plant community structure require more empirical attention. In terms of application, the role of plant-microbe feedback on the restoration of degraded grassland is clarified to guide grassland management.