Productivity improvement mechanism of mixed forest plantations driven by underground factors

A large area of plantation has been built worldwide due to site restriction, commercial need and other reasons, which plays an important role in wood production, landscape construction, environmental improvement and climate change mitigation. However, the decrease of productivity and biodiversity caused by monoculture management are the main problems restricting its development. The purpose of constructing mixed forests is to avoid the above problems in monoculture and maximize the benefits of plantation. Due to the long periodicity of forest growth, the complexity of forest environment and the characteristics of soil “black box”, it is challenging to explore the process of underground ecosystem. At present, the research on the mechanism of increasing yield of mixed forests mainly focuses on the above-ground parts such as tree species composition and stand structure, and the exploration of subsurface factors mainly focuses on soil nutrient content and turnover process. Subsurface niche separation, competition reduction and promotion caused by niche complementarity are the main mechanisms of species coexistence in mixed forests, which is conducive to resource acquisition of mixed tree species. The response of root plasticity to interspecific interaction is another mechanism for plants to avoid direct competition for limited resource. Both may even lead to an “overyielding effect”. Changes in root secretions and soil microorganisms caused by plant-soil feedback have important effects on physiological and ecological processes in some mixed forests. Thus, niche complementarity and plant-soil feedback largely determine the productivity and sustainability of mixed forests. In view of this, the purpose of this paper is to elaborate the underground interactions of successful mixed forests based on niche complementarity and plant-soil feedback theory, in an effort to deepen our understanding of the changes and regulatory mechanisms of subsurface resource acquisition strategies of trees in mixed forests, and the shortcomings and prospects of current research were proposed.