两种轮作模式下秸秆还田对土壤呼吸及其温度敏感性的影响

通过分析不同作物轮作模式下秸秆还田对土壤呼吸及其温度敏感性的影响,为深入探究关中地区农田生态系统碳循环提供理论依据。试验设置于陕西省杨凌地区,在2012年10月至2014年9月期间以冬小麦-夏玉米轮作模式和冬小麦-夏大豆轮作模式作为研究对象,分别设置秸秆还田(SM)和秸秆不还田(NS)两个处理,测定分析不同处理下土壤呼吸、土壤温度及土壤含水量的变化趋势和差异,并估算土壤呼吸的温度敏感性(Q_(10))。结果表明:土壤呼吸存在明显的季节变化,在作物生育期大部分时间内,SM处理的土壤呼吸速率均显著高于NS处理(P0.05),且SM处理的作物生育期土壤呼吸平均速率及土壤呼吸累计排放量也极显著高于NS处理(P0.01);不同作物生育期土壤呼吸平均速率依次为夏玉米夏大豆冬小麦,土壤呼吸总量表现为冬小麦夏玉米夏大豆、冬小麦-夏玉米轮作冬小麦-夏大豆轮作。冬小麦-夏玉米轮作与冬小麦-大豆轮作的土壤温度间存在差异;其中,在冬小麦生育前期,冬小麦-夏玉米轮作的土壤温度显著高于冬小麦-大豆轮作;第2季夏玉米生育期内5 cm深度的土壤温度显著低于同季的夏大豆;相比NS处理,SM处理能提高冬季土壤的温度,并降低春季和夏季的土壤温度;在高温少雨的时期内,SM处理能够提高0~30 cm土壤的平均含水量,不同的前茬作物引起两种轮作模式中冬小麦耕作层土壤含水量间明显的差异,夏玉米耕作层土壤含水量显著高于夏大豆。相关分析表明,土壤呼吸与5 cm和10 cm土壤温度均存在极显著的正相关性,且与5 cm土壤温度的相关性更好;但土壤呼吸与0~30 cm的土壤平均含水量无显著相关性。5 cm和10 cm土壤温度变化能够分别解释土壤呼吸变化的64.6%~67.3%和51.5%~59.6%。整个研究周期内,温度敏感性(Q_(10))为1.70~2.01,冬小麦-夏玉米轮作的温度敏感性显著高于冬小麦-大豆轮作,且同一轮作模式下SM处理的温度敏感性显著低于NS处理。因此,秸秆还田能够提高农田的土壤呼吸作用,降低土壤呼吸的温度敏感性,同时能够调节土壤的水热状况。

Effect of straw mulching on soil respiration and its' temperature sensitivity under different crop rotation systems

Soil respiration is the second largest source of terrestrial carbon (C) flux between the atmosphere and the terrestrial eco-systems. It is critical for regulating global soil C dynamics. As soil temperature and soil moisture would exert stronger effects on soil respiration in the future, a thorough understanding of the response of soil microbes to temperature change can provide a novel method of studying the effects of drought on soil respiration and of predicting drought-induced changes in future terrestrial C cycle. Temperature sensitivity of soil respiration can explain the relationship between soil respiration and soil temperature. The objective of this study was to explore the effects of straw mulch on the linkages between the changes in soil respiration and temperature. The study aimed to lay the basis of C cycle process in agro-ecosystems in Yangling, Shaanxi province. To that end, a 2-year field experi-ment (October 2012 to September 2014) was conducted to study the linkages under different crop rotation systems. It included two treatments of no straw (NS) and straw mulch (SM) in winter wheat-summer maize rotation and winter wheat-summer soybean rotation systems. Soil respiration rate, temperature, and moisture were analyzed under different crop rotation systems. In addition, the Q10 (withQ10 value as the multiplier in determining soil respiration rate after temperature increase of 10℃) was used to determine the effect of soil temperature change on soil respiration. It was noted that SM significantly (P < 0.05) increased soil respiration rate during crop growth period. Mean soil respiration rate and cumulative soil respiration during crop growth period significantly in-creased under straw mulch (P < 0.01). The order of mean soil respiration rate under various crops was as follows: maize (3.401–4.810μmol.m-2.s-1) > soybean (3.390–3.762μmol.m-2.s-1) > wheat (2.673–3.141μmol.m-2.s-1). Then the order of cumula-tive soil respiration among different rotations was as follows: wheat-maize 34.68–40.81 t(CO2).hm-2] > wheat-soybean 30.04–33.86 t(CO2).hm-2]. In addition, soil temperature varied significantly (P< 0.05) among different crops. Particularly, soil temperature under wheat-maize rotation system was higher than that under wheat-soybean rotation system during the growth stage of wheat. Soil tem-perature at 5 cm soil depth in maize field was higher than that in soybean field during the summer of 2014. It was noted that SM treatment was a major regulator of soil temperature — significantly increasing it in winter and then significantly decreasing it in spring and summer. Moreover, mean soil moisture content in the 0–30 cm soil layer was significantly higher under SM treatment than under NS treatment during the dry season. Further, mean soil moisture content in the 0–30 cm layer during wheat growth period var-ied significantly among different crop rotation systems, which was associated with root characteristics under crop rotation. The mean soil moisture content for the 0–30 cm soil layer during maize growth period was significantly higher than that during soybean growth period. Soil temperature at the 5–10 cm soil layer was positively correlated with soil respiration. However, soil moisture at the 0–30 cm soil layer was not significantly correlated with soil respiration. Changes in soil temperature at 5 and 10 cm soil depths were re-spectively 64.6%–67.3% and 51.5%–59.6% explained by the variance in soil respiration. In this study,Q10 varied within 1.70?2.01 across different crop rotation systems and was significantly higher under wheat-maize than wheat-soybean rotation system. In addi-tion,Q10 was significantly higher under SM treatment than under NS treatment. Therefore, SM treatment was more advantageous in terms of the ability to effectively reduce temperature sensitivity of soil respiration and to accurately predict soil moisture and soil heat conditions.