Asymmetric soil respiration responses to pulse rainfall in thinned subtropical Cunninghamia lanceolata plantations

We investigated the impact of rainfall events during the inactive growing season (winter) on soil respiration pulse in a subtropical Chinese fir ecosystem. Single rainfall events of varying intensities induced significant pulse effects on soil respiration. Although thinning reduced root biomass by 63.5%, it increased soil temperature by 0.4°C (17.4%) and microbial carbon content by 48.49 mg kg⁻¹ (37.9%). The reduction in root respiration balanced by increased microbial respiration resulted in non-significant changes in soil respiration pulse effects post-thinning. Soil respiration pulse effects were amplified under reduced and mildly increased rainfall compared to control conditions. However, under high-intensity rainfall, the pulse effect diminished, indicating an asymmetric response. Structural equation modeling revealed that sustained changes in rainfall altered soil aeration, influencing root and microbial growth and metabolism, leading to asymmetric soil respiration pulse effects.本研究针对中国亚热带杉木生态系统中生长休眠季（冬季）的降雨事件对土壤呼吸脉冲（soil respiration pulse）的影响展开了调查。不同强度的单次降雨事件均会对土壤呼吸产生显著的脉冲效应。尽管间伐使根系生物量降低了63.5%，但同时将土壤温度提升了0.4℃（增幅17.4%），并使微生物碳含量增加了48.49 mg·kg⁻¹（增幅37.9%）。根系呼吸的减少与微生物呼吸的增加相互抵消，使得间伐后土壤呼吸脉冲效应未出现显著变化。 与对照处理相比，降雨量减少及小幅增加的处理均会增强土壤呼吸脉冲效应。但在高强度降雨条件下，脉冲效应反而减弱，这表明土壤呼吸脉冲效应存在不对称响应特征。结构方程模型分析结果显示，降雨量的持续性变化会改变土壤通气性，进而影响根系与微生物的生长及代谢活动，最终导致土壤呼吸脉冲效应呈现不对称响应。