Greater root biomass offsets soil organic carbon loss under climate impact in rice paddies

Abstract

Changes in temperature and atmospheric carbon dioxide (CO₂) concentrations can significantly influence the dynamics of soil organic carbon (SOC). This is particularly relevant for rice paddy agriculture, which currently accounts for 14 % of the SOC stock in arable land and is expected to expand due to the increasing global demand for rice. We conducted a field study using large open-top chambers to evaluate the impact of future climatic conditions (+2 °C, +200 ppm CO₂) on SOC and its accrual mechanisms in paddy soils. Three years of simulated change increased mineral-associated organic carbon (MAOC) but did not alter bulk SOC or other soil C fractions (free light fraction, occluded light fraction, and sand-associated). During the tillering stage, when root formation is most active, future climatic conditions increased soluble organic C, root biomass growth, and CO₂ and CH₄ emissions, indicating enhanced SOC mineralization and microbial activity. Stable carbon isotopes revealed that plant-derived MAOC formation increased under future climatic conditions, while the plant-derived free light fraction decreased. Together, these findings demonstrate that enhanced root growth during paddy rice cultivation offsets SOC loss through soil respiration in response to environmental change conditions. This underscores the need for soil management practices that maintain root inputs to support sustainable rice cropping under a changing environmental condition.