Global warming decreased soil organic carbon stock in rice paddy via increasing organic matter lability and heterotrophic respiration

초록

Global warming can simultaneously increase plant net primary production (NPP) as a carbon (C) input and microbial decomposition of organic matter as a C output, making it challenging to predict its overall impact on soil organic C (SOC) accumulation. To evaluate the effects of global warming on SOC dynamics in paddy soils, current and projected climate conditions (+2 degrees C and +200 ppm CO2) were simulated using Open Top Chambers with chemical and organic fertilizer treatments. Chemical or organic fertilizer treatments were added in both climate conditions. In the organic fertilizer plots, cover crops were cultivated during the cold fallow season and fully incorporated as green manure before rice transplanting. Changes in SOC stock during the cropping period were assessed using a net ecosystem C budget analysis, representing the balance between C inputs and outputs. Global warming reduced rice NPP by 5-16% under the same fertilization, while increasing microbial decomposition of organic matter by 28-98%. It also substantially increased dissolved organic matter in the soil without discriminating against chemical composition, further enhancing microbial decomposition. Consequently, SOC accumulation was markedly decreased under future climate conditions. While the cultivation and incorporation of cover crops increased SOC under current climate conditions, this practice was insufficient to enhance SOC accumulation under projected future climates. Overall, under future climate conditions, larger amounts of organic amendments may be required to achieve meaningful increases in SOC storage.

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