Tea-woody plant intercropping improves soil quality and ecosystem multifunctionality in the acidic tea plantation system.

Tea plantations under monoculture experience soil degradation and reduced ecosystem services, highlighting the need for sustainable alternatives. Agroforestry is increasingly recognized as a sustainable farming method that can improve soil ecosystem services. Though research has shown that intercropping tea with woody plants can improve certain soil properties, the mechanisms via which agroforestry simultaneously affects soil quality and ecosystem multifunctionality (EMF), and the dominant biogeochemical factors [carbon (C), nitrogen (N), or phosphorus (P) cycling] driving these changes remain poorly understood. Therefore, the present study compared soil characteristics, enzyme activities, ecoenzymatic stoichiometry, soil quality index (SQI), and EMF among tea monoculture (CK, control), tea-avocado intercropping (TA), and tea-macadamia intercropping (TM) systems in a plantation in China. Our initial analysis indicated that both TA and TM significantly increased soil organic carbon (SOC), dissolved organic nutrients, available and microbial phosphorus (P), and β-glucosidase, N-acetyl-glucosaminidase, and acid phosphatase activities, but reduced the ecoenzymatic C:P ratio and vector length compared to CK; these changes indicated decreasing microbial C limitation but persistent N limitation. Consequently, both SQI (186-295%) and EMF (139-149%) were enhanced under the tea-woody plant intercropping system. Random forest modeling and simple linear regression identified that the metrics associated with the P cycle were the primary drivers of EMF. Thus, our study proves that tea-woody plant intercropping enhances soil multifunctionality primarily by stimulating P cycling and increasing bioavailable P, with a moderate improvement in C supply. The study also indicates that intercropping is a viable strategy for improving soil health and agricultural sustainability in P-limited acidic soils.