降雨对旱作春玉米农田土壤呼吸动态的影响

土壤呼吸是调控全球碳平衡和气候变化的关键过程之一,降雨作为重要的扰动因子,在不同区域和不同环境条件下,对土壤呼吸具有复杂的影响.研究降雨对农田土壤呼吸及其分量的影响,对准确预测未来气候变化下陆地生态系统碳平衡具有重要意义.对黄土高原东部典型春玉米农田生态系统生长季内3次降雨前后土壤呼吸及其分量进行了原位连续观测,结果表明:在土壤湿润的条件下,降雨对春玉米农田土壤呼吸及其分量具有明显的抑制作用,在土壤湿度大于27％后土壤呼吸及其分量随土壤湿度上升呈明显下降,且对温度的敏感性降低.土壤呼吸及其分量在降雨前后的变化受土壤温度和土壤湿度的共同影响.降雨量、降雨历时和雨前土壤含水量决定了土壤呼吸及其分量对降雨响应的程度和时长.土壤呼吸及其分量对土壤温度的敏感性各不相同,微生物呼吸对温度的敏感性最高,Q10为5.14;其次是土壤呼吸,Q10为3.86;根呼吸的温度敏感性相对最低,Q10为3.24.由于土壤呼吸分量对温度和湿度的敏感性不同,降雨后根呼吸的比例有所升高.

The impact of rainfall on soil respiration in a rain-fed maize cropland

The research on the impact of rainfall on soil respiration is significant to predict accurately the carbon balance of terrestrial ecosystems under future climate change. It is consensus that a certain degree of drought would suppress soil respiration, as well as the processes of water, carbon and nitrogen would be excited after re-watering by precipitation or irrigation. However, some research showed the suppression of soil respiration by precipitation. As a disturbance factor, the effect of precipitation on soil respiration is complex because of different vegetation and soil type in different regions. It is necessary to reveal the impact of rainfall amount, intensity and duration on soil respiration under different soil water content, as well to make clear the turning point of suppression or excitation of soil respiration in different regions. In a maize cropland located at eastern Loess Plateau, soil respiration and its components was measured continuously around 3 rainfall incidents based on in situ observation technique, and the impact of rainfall on soil respiration and its components was analyzed. The study was conducted in Shouyang county, Shanxi Province. It is a semi-humid area. The seasonal variation of precipitation is large, about 70% of annual amount occurs from June to September. In the field of maize cropland, soil respiration and its components were measured continuously by LI-8150 Soil CO₂ Flux System. Soil respiration was divided into microbial respiration and root respiration respectively based on root exclude method. Each treatment was repeated twice, and there were 4 observation fields in total. There were 3 rainfalls recorded during July and August, and we analyzed the variation of soil respiration and its components before and after the 3 rainfalls. The results showed that rainfall suppressed the soil CO₂ efflux obviously under high soil water content. When soil volumetric water content was higher than 21.2%, 20.7% and 21.8%, respectively, soil respiration, microbial respiration and root respiration decreased obviously with the increase of soil water content, and the sensitivity of soil respiration to soil temperature also decreased. The variation of soil respiration and its components were influenced by both soil temperature and moisture. The amount and duration of rainfall and soil water content before rainfall decided the intensity and duration of response to precipitation. The temperature sensitivity of soil respiration and its components were different with each other. The temperature sensitivity of microbial respiration was the highest, Q₁₀ was 5.14, and the second highest was soil respiration with Q₁₀ 3.86. The temperature sensitivity of root respiration was the lowest, and Q₁₀ was 3.24. The ratio of root respiration to soil respiration increased after rainfall because the different sensitivity of respiration to temperature and moisture. Two factor model, including soil temperature and soil water content, was able to evaluate the response of soil respiration and microbial respiration to the variation of environmental factors in the maize ecosystem.