Spatially Contrasting CO₂ Dynamics Driven by Green Manure Intercropping in Subtropical Tea Plantations

Abstract. Tea plantations are important contributors to greenhouse gas emissions due to intensive fertilization and continuous cultivation. However, the mechanisms by which green manure intercropping regulates soil CO₂ dynamics in these systems remain poorly understood. We investigated how intercropping with Vulpia myuros (SM) and a legume–nonlegume mixture of Lolium perenne and Trifolium repens (HM) influenced spatial CO₂ flux dynamics compared with a no-intercropping control (CK) from tea rows and inter-row zones in a subtropical tea plantation. Distinct seasonal variations were observed, with CO₂ fluxes peaking in summer and autumn and declining in spring and winter. Average tea-row fluxes were 7.41 ± 0.45, 7.35 ± 0.44, and 8.12 ± 0.46 mg·m⁻²·min⁻¹ under SM, HM, and CK, respectively, indicating emission reductions with intercropping. In contrast, inter-row fluxes were higher under SM (10.83 ± 0.52 mg m⁻² min⁻¹) and HM (9.77 ± 0.54 mg m⁻² min⁻¹) than under CK (9.07 ± 0.44 mg m⁻² min⁻¹), demonstrating pronounced spatial contrasts. Diurnal patterns exhibited midday peaks (12:00–14:00), especially in spring and summer, and short-term CO₂ pulses were triggered by field operations such as fertilization and pruning. Notably, HM effectively suppressed fertilization-induced CO₂ pulses, revealing the mitigation potential of legume–nonlegume mixtures. Green manure increased soil organic carbon (6.4 %), lowered soil temperature (4.5 %), and enhanced porosity (4.2 %), collectively shaping CO₂ dynamics. Multivariate analysis identified soil organic carbon (SOC) and temperature as dominant flux drivers, and a potential SOC threshold was detected, beyond which CO₂ emissions accelerated. While intercropping reduced tea-row emissions by 7.1–7.9 % but increased inter-row emissions by 12.7–28.9 %, continuous intercropping significantly decreased overall inter-row emissions over time. These results highlight the spatially heterogeneous nature of carbon flux regulation and demonstrate the long-term potential of green manure intercropping as a climate-smart management strategy in perennial agroecosystems.