黄土旱塬区免耕玉米田土壤呼吸对降雨的响应

在多年定位试验的基础上,采用LI-8150-16多通道土壤碳通量测量系统对传统耕作和免耕处理下玉米田的土壤呼吸进行了连续观测,以探讨不同耕作措施处理下土壤呼吸对降雨的响应。结果表明:降雨发生瞬间,土壤呼吸受应激反应影响迅速降低,传统耕作和免耕处理下分别较降雨前降低62.9%—92.9%和35.8%—56.9%;降雨后,传统耕作和免耕处理土壤呼吸的降幅范围分别为31.5%—89.2%和15.7%—59.9%;土壤体积含水量接近于18%时,传统耕作下土壤呼吸比免耕下高51.8%,当土壤体积含水量高于30%时,传统耕作下土壤呼吸比免耕处理下低43.0%,表明传统耕作土壤呼吸更易受土壤水分的影响,波动幅度大;传统耕作处理下土壤呼吸随土壤温度的升高而增大,免耕处理下土壤呼吸随土壤温度的升高变化不明显;土壤体积含水量较小(20%)时,不同耕作处理下土壤呼吸均随土壤含水量增加而增加,含水量较高(30%)时则均随土壤含水量的升高而减小,两种情况下均为免耕处理的变化速率更大;双因子线性模型可较好地描述玉米田土壤呼吸对温度和水分变化的响应。

Response of soil respiration of corn field under no tillage to precipitation events in loessial tablelands

Soil respiration in terrestrial ecosystems plays an important role in global carbon cycling. However, our understanding of the effects of precipitation on soil respiration is still very limited, particularly for conservation agricultural systems. This study was conducted to investigate the effects of long-term no-till practice on soil respiration in a corn field under rain-fed conditions in the loessial tablelands of northwest China. The no-till experiment was established in a maize/winter wheat/soybean rotation field in 2001 at Qingyang Experimental Station of Lanzhou University, which is located in the east of Gansu Province and in the rain-fed agricultural production zone of the western Loess Plateau. Experiments examining the effects of precipitation events on fluctuations in soil respiration were carried out in July 2013 under tillage and no-till conditions. Soil respiration was measured using the LI-8150-16 multi-channel soil carbon flux measurement system, which also recorded synchronous soil moisture and soil temperature data. The dynamics of soil respiration before and after several precipitation events were analyzed and relationships between soil respiration and factors affecting it (mainly soil temperature and soil water conditions) were examined. Soil respiration decreased immediately when rainfall occurred; soil respiration under tillage and no-till treatments decreased by 62.9%-92.9% and 35.8%-56.9%, respectively. After the precipitation event, soil respiration under tillage and no-till decreased by 31.5%-89.2% and15.7%-59.9%, respectively, from soil respiration before the precipitation event. Soil respiration under tillage was 51.8% higher than that under no-till when soil water content was around 18%, while soil respiration under tillage was 43.0% lower than that under no-till when the soil water content was over 30%, indicating that soil respiration under tillage was more sensitive to soil water content. Soil respiration under both treatments had a linear relationship with soil temperature. Soil respiration under both treatments increased with soil temperature; however, the linear relationship under tillage (R²=0.56) was more significant than that under no-till (R²=0.36), indicating that the soil respiration under tillage was more sensitive to soil temperature. Soil respiration was also significantly linearly related to soil water content (P < 0.05). Under both tillage treatments, soil respiration increased with soil water content when the soil volumetric water content was below 20%, while soil respiration decreased as soil water content increased when the soil volumetric water content was over 30%. The responses of soil respiration to the synergic effects of soil temperature and soil water content could be satisfactorily described with the two-factors linear model under both treatments (P < 0.001), although the correlation coefficient under tillage treatment was higher than that under no-till treatment. The results presented in this work will serve as a basis for further research on the mechanisms by which precipitation affects soil respiration, and can also help to evaluate the effects of the no-till practice on the carbon balance of terrestrial ecosystems under rain-fed conditions.