脉冲式降水对不同类型草地土壤微生物呼吸碳释放量的影响

降水事件引起土壤短时间内释放大量CO_2的现象常称为降水脉冲效应。降水事件发生后,由于水分和养分可获得性快速提升使土壤微生物呼吸速率快速升高至正常水分状况的数倍,从而导致土壤CO_2大量释放并一定程度上影响着生态系统碳循环过程和土壤碳平衡,尤其在干旱或半干旱地区。利用自主研发的能快速测定土壤微生物呼吸速率的装置,对内蒙古三类典型草原(草甸草原、典型草原和荒漠草原)土壤分别开展土壤复湿实验(60%饱和含水量),并采用高频测定(48 h测定288次)。在土壤复湿后在所有温带草地类型中均发生了明显的脉冲效应,降水脉冲过程中单位有机质(土壤有机碳,SOC)最大呼吸速率(R_(SOC-max))整体表现为荒漠草原(1.59 mg C g~(-1) SOC h~(-1))草甸草原(0.73 mg C g~(-1) SOC h~(-1))典型草原(0.50 mg C g~(-1) SOC h~(-1));而脉冲效应的持续时间(Duration)则表现为典型草原(2.5 h)草甸草原(1.5 h)荒漠草原(0.67 h)。在土壤复湿48 h内,单位土壤微生物呼吸累积量(A_(R_(Soil)))的大小规律与单位土壤微生物呼吸速率R_(Soil)一致,均为典型草原草甸草原荒漠草原;然而,如果用土壤有机质进行标准化,单位有机质呼吸累积量A_(R_(SOC))表现为荒漠草原(9.74 mg C g~(-1) SOC)典型草原(6.54 mg C g~(-1) SOC)草甸草原(3.54 mg C g~(-1) SOC),与当地年降雨频率呈负相关关系,表明降水脉冲效应与土壤长期经历的干旱状况存在密切关系。本研究结果不仅证明在干旱半干旱区域降水脉冲效应的普遍性,同时还启发我们应从国家或区域尺度开展研究,以进一步揭示土壤基质含量、土壤干旱状况等对降水脉冲效应的影响。

Effects of precipitation pulse on soil carbon released by microbes in different grasslands

The phenomena that precipitation events cause a large amount of CO₂ release from the surface soil in a short time is also known as the Birch Effect. The respiration rate of soil microbes can increase rapidly within a few minutes of precipitation. The significant effects on soil carbon emission may affect the soil carbon cycle process of the terrestrial ecosystems, especially in arid and semi-arid regions. In order to explore the effects of precipitation pulse on grassland soils, we conducted a simulated precipitation to test soil microbial respiration rate R_S in three typical grassland types (meadow grassland, typical grassland, and desert grassland) in Inner Mongolia, China, by using a self-developed high-intensity measurement system (288 measurements within 48 h). The results showed that, in all three grassland soils, the pulse in the microbial respiration per gram of soil organic carbon (SOC,R_SOC) peaked within 10 min of the simulated precipitation. The maximum R_SOC (R_SOC-max) was significantly high in desert grassland (1.59 mg C g^-1 h^-1), followed by meadow grassland (0.73 mg C g^-1 h^-1) and typical grassland (0.50 mg C g^-1 h^-1). Furthermore, the accumulative microbial respiration per gram of soil (A_RSoil was similar to the microbial respiration per gram of soil (R_Soil). Both were the highest in typical grassland, followed by meadow grassland and desert grassland. If it was standardized by SOC, the accumulative microbial respiration per gram of SOC (A_RSOC was the highest in desert grassland (9.74 mg C g^-1), then meadow grassland (6.54 mg C g^-1), and the lowest in typical grassland (3.54 mg C g^-1).This indicates that the soil respiration response to pulse precipitation is closely related to the degree of drought. Our findings demonstrated the importance of precipitation pulse on soil carbon cycles. Therefore, future studies should consider the effects of soil substrate and initial soil water content.