Spatially contrasting CO 2 dynamics driven by green manure intercropping in subtropical tea plantations

Abstract

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 employed the static chamber method over a 2-year period, with sampling conducted weekly, to investigate how intercropping with Vulpia myuros C. (SM) and a legume–nonlegume mixture of Lolium perenne L. and Trifolium repens L. (HM) influenced spatial soil 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 soil CO2 fluxes peaking in summer and autumn and declining in spring and winter. Diurnal patterns generally exhibited midday peaks (12:00–14:00, local time), especially in summer and autumn across all tea-rows, 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 soil CO2 dynamics. Multivariate analysis identified soil organic carbon (SOC) and temperature as dominant flux drivers, hinting at a possible SOC threshold that warrants further validation. Compared to CK, intercropping reduced tea-row emissions by 7.1 %–7.9 % but increased inter-row emissions by 12.7 %–28.9 % based on the two years cumulative emissions, continuous intercropping exhibited a trend of reducing inter-row CO2 emissions, indicating its potential mitigation value. These results highlight spatially heterogeneous soil CO2 flux and suggest that green manure intercropping has long-term potential as a climate-smart practice for soil carbon management in tea plantations.