Green manure species composition differentially regulates soil N₂O emissions and their environmental drivers in subtropical tea plantations

Abstract

Green manure intercropping is widely advocated for improving soil fertility in perennial cropping systems, yet its effects on soil N₂O emissions remain poorly quantified in tea plantations. This study assessed N₂O fluxes under three intercropping regimes, i.e., no intercropping (CK), single‑species green manure (SM), and legume‑based mixed green manure (HM), in a subtropical tea plantation. N₂O fluxes exhibited pronounced temporal dynamics, with seasonal means ranked as spring > summer > autumn > winter and treatment means followed SM > HM > CK. Compared with CK, total annual emissions increased by 38.5% under SM and 19.2% under HM; however, HM exhibited significantly lower N₂O emissions than SM, indicating that green manure species composition influenced the magnitude of the emission increase. Field operations, particularly tea harvesting, pruning, and fertilization, triggered strong short-term N₂O pulses, while green manure growth exerted sustained control over long-term emission dynamics. Green manure intercropping enhanced soil moisture retention and altered soil nutrient status, thereby modifying soil environmental conditions associated with N₂O emissions. Piecewise structural equation modeling (SEM) identified soil temperature (ST), water-filled pore space (WFPS), and total nitrogen (TN) as important environmental factors associated with N₂O fluxes across treatments, explaining 59–74% of the variance. Soil organic carbon (SOC) and TN represented important components of soil carbon and nitrogen pools associated with N₂O emissions. TN dominated under HM, whereas the SM exhibited a more complex network involving NO₃⁻-N, SOC, and pH; and CK was governed primarily by ST and WFPS. Overall, green manure species composition substantially influenced N₂O emissions in the tea plantation. Although both green manure treatments increased cumulative N₂O emissions relative to CK, the legume-based mixture produced lower emissions than the single-species green manure treatment.