Soil Moisture as a Key Regulator of Organic Carbon Stabilisation and CO2 Fluxes Across Agroecosystems: A Systematic Review

Soil moisture plays a critical role in soil organic carbon (SOC) storage and stabilisation and carbon dioxide (CO2) emissions amid climatic variability and in different agroecosystems. However, the mechanisms that regulate organic matter decomposition, microbial activities, and root respiration with direct impacts on carbon (C) cycling remain incompletely synthesised. This review synthesises evidence showing how soil moisture regulates SOC stabilisation and CO2 fluxes, particulate organic C (POC) and mineral-associated organic C (MAOC) response and the role of rare microbes under drought. Findings from 87 peer-reviewed studies from Web of Science and Scopus between 2007 and 2026 confirm that soil moisture is a key regulator of C circulation. Additionally, moderate soil moisture of a 60–70% water-holding capacity (WHC) enhances SOC stocks and CO2 efflux peaks due to increased microbial activities and respiration. Extreme drying and rewetting cycles in rainfed soils trigger drastic CO2 emission pulses. However, under drought conditions, rare microbes can be utilised (for rhizosphere modification) to improve microbial biomass C (MBC), necromass C and MAOC formation, thereby enhancing sustainable agricultural production. This study confirms that CO2 efflux and SOC stabilisation primarily rely on soil moisture dynamics. Therefore, sustainable moisture conservation practices improve moisture retention and SOC stabilisation and reduce CO2 emissions, offering a viable pathway for mitigating the impacts of climate change footprints.