Effects of cover cropping on orchard soil microbiomes: Mechanisms and perspectives.

Orchards have long faced severe soil erosion, acidification of red soils, low nutrient-use efficiency, and frequent soil-borne diseases. Conventional clean tillage combined with intensive chemical inputs often fails to simultaneously improve fruit yield and quality while safeguarding orchard ecological security. Cover cropping (i.e., managed groundcover vegetation) introduces persistent surface plant cover and introduces continuous inputs of root exudates, litter, and residues, while simultaneously modifying soil moisture, temperature, aggregation, porosity, and nutrient availability. Consequently, it reorganizes the soil microbiome from the rhizosphere scale to community-network scales and drives key ecological processes such as carbon sequestration, nitrogen and phosphorus turnover, and disease suppression. Mechanistically, cover crops (i) enhance the supply of labile carbon through root exudation and residue return, stimulating microbial assimilation and enzyme-mediated decomposition and promoting SOC stabilization via microbial necromass formation-mineral association/aggregate protection; and (ii) optimize microbial habitats by improving aggregate architecture, pore structure, and water-holding capacity, and by regulating pH and nutrient availability, thereby increasing the abundance and functional potential of key guilds (e.g., diazotrophs, nitrifiers/denitrifiers, and microorganisms involved in organic-P mineralization) and their functional gene repertoires. In addition, cover cropping may strengthen system stability and suppressiveness through multi-trophic interactions and reconstruction of the soil micro-food web. However, under drought conditions or during the juvenile-tree stage, trade-offs can emerge due to context-dependent tree-groundcover competition for water and nutrients. Future progress requires long-term field experiments integrating multi-omics, isotope tracing, and process-based flux measurements to establish causal evidence chains and scenario-specific models linking management-microbial mechanisms-ecosystem services. Developing operational microbiome-based indicators will provide a scientific basis for groundcover species selection, cover pattern optimization, and fertilizer reduction with improved efficiency, as well as disease mitigation and fruit-quality enhancement.