降雨引起的干湿交替对土壤呼吸的影响:进展与展望

Effects of drying-wetting cycle caused by rainfall on soil respiration: Progress and prospect

土壤呼吸是全球陆地生态系统碳循环重要组成部分,降雨作为扰动因子对土壤呼吸动态的改变将直接影响全球碳平衡。探讨降雨对土壤呼吸的作用机制是陆地生态系统碳循环和碳收支研究的重要内容。本文综述了近年来国内外学者关于降雨引起的干湿交替对土壤呼吸影响机制的研究进展,阐述了土壤水分对土壤呼吸的影响及其机理。土壤水分在适宜范围内促进土壤呼吸,过高或过低均抑制土壤呼吸;降雨引起的干湿交替通过改变土壤水分影响土壤呼吸。一方面,干旱条件下,降雨引起的干湿交替主要通过短时间置换土壤中CO_2、增加土壤微生物呼吸底物、提高微生物活性、增强凋落物分解速率等途径提高土壤呼吸速率。另一方面,湿度较高的土壤经过短时间降雨迅速达到水分饱和或积水状态,降雨引发的干湿交替通过限制O_2进入土壤,形成厌氧环境,抑制微生物和根系呼吸。此外,降雨引发的干湿交替还通过地表积水淹没部分植株,降低植物叶面积,减少光合产物,显著抑制根系呼吸。为更准确估算降雨变化影响土壤呼吸对陆地生态系统碳平衡的干扰,提出了未来降雨对土壤呼吸影响研究需重点关注的3个方面:(1)降雨对土壤呼吸影响的微生物响应机制;(2)区分土壤自养呼吸和异养呼吸对降雨的响应机制;(3)降雨对土壤呼吸影响模型研究。

Soil respiration is an important part of the carbon cycle in terrestrial ecosystems. The changes of soil respiration caused by rainfall directly affect global carbon balance. Therefore,it is important to explore the mechanism underlying the effects of rainfall on soil respiration,which is necessary for understanding the carbon cycle and carbon budget of terrestrial ecosystems. Here,we summarized the research progress on the mechanism of drying-wetting cycle caused by rainfall on soil respiration. Soil respiration can be promoted at intermediate moisture conditions,but suppressed in both wetter and drier conditions. Drying-wetting cycles caused by rainfall affect soil respiration by changing soil moisture. On one hand,under the condition of drought,drying-wetting cycle caused by rainfall improve soil respiration rate by short-term replacement of CO2 in soil,increases of soil microbial respiratory substrate, increases of microbial activity, and enhancement of litter decomposition. On the other hand,soils with high moisture could reach saturation more quickly or even be waterlogged after a short period of rainfall. Drying-wetting cycle caused by rainfall can significantly suppress soil respiration through restricting the entrance of O2 to the soil,forming an anaerobic environment,and inhibiting microbial and root respiration. In addition,drying-wetting cycle caused by rainfall could significantly inhibit root respiration by flooding part of the plant,reducing plant leaf area and photosynthetic products. In order to accurately estimate the interference of soil respiration on carbon budget of terrestrial ecosystems,future studies on the effects of rainfall on soil respiration should focus on three aspects:( 1)microbiological response mechanisms underlying the effects of rainfall on soil respiration;( 2)differentiating response mechanisms of soil autotrophic respiration and heterotrophic respiration to rainfall;and( 3) modeling the effect of rainfall on soil respiration.