CO_(2)浓度升高及增温下谷子土壤酶活性及其温度敏感性

Effects of elevated CO_(2) and warming on soil enzyme activity and temperature sensitivity of millet

研究作物重要生长阶段土壤酶活性及其温度敏感性对CO_(2)浓度升高及增温的响应,对于评价气候变化对作物生产的影响以及评估土壤生态系统的功能稳定性具有重要意义。利用人工气候室模拟不同水分(充分供水和轻度干旱)、CO_(2)浓度升高(由400μmol·mol^(-1)升高至700μmol·mol^(-1))和增温(由22℃升高至26℃)条件,以3个因素交互作用下盆栽谷子(Setaria italica)土壤为研究对象,分析了谷子灌浆期土壤中β-葡糖苷酶(βG)、β-N-乙酰葡糖苷酶(NAG)、纤维素酶(CBH)和β-木糖苷酶(βX)活性的温度敏感性。结果表明,对照(CK)在充分供水条件下土壤βG、NAG、CBH和βX的酶活性随着培养温度增加呈先升高后降低的趋势,在25℃时酶活性最高。在最适温度下(25℃),与CK相比,CO_(2)浓度升高使谷子灌浆期土壤βG酶活性显著降低,而对土壤NAG、CBH、βX酶活性的抑制作用较小;CO_(2)浓度升高和增温的交互作用在不同水分条件下表现不同,具体表现为轻度干旱条件下酶活性受到抑制,而充分供水时无显著差异。此外,CO_(2)浓度和温度显著影响谷子灌浆期土壤酶活性的温度敏感性(Q_(10))CO_(2)浓度升高使土壤胞外酶活性的Q_(10)显著增大,而增温使Q_(10)相对减小。在充分供水条件下,增温抵消了CO_(2)浓度升高对酶活性Q_(10)的影响,二者的交互作用对Q_(10)无显著影响。然而,在轻度干旱条件下,CO_(2)浓度升高和增温对Q_(10)影响显著,即CO_(2)浓度、温度及水分三者对Q_(10)的交互作用显著。同时,CO_(2)浓度与水分对Q_(10)有显著的交互作用,但与仅CO_(2)浓度升高以及3个因素交互作用的影响无明显差异。冗余分析显示,除CO_(2)浓度和温度外,Q_(10)还受到微生物量、土壤养分等环境因子的影响。本研究表明CO_(2)浓度、温度和水分以及三者之间的交互作用对土壤酶活性及其温度敏感性的影响复杂,特别是CO_(2)浓度升高抑制了土壤酶的温度敏感性,减弱了土壤碳氮循环相关酶的代谢功能及其稳定性,进而影响土壤生态系统的功能稳定性。

Study on the response of soil enzyme activity and temperature sensitivity to elevated CO_(2)concentration and warming at important growth stages of crops is of great significance to evaluate the impact of climate change on crop production and the functional stability of soil ecosystem.In view of this,the soil of millet(Setaria italica)at grain filling stage was selected as the research object for pot experiments,and three climate scenarios were designed using an artificial climate chamber as follows:elevated CO_(2)concentration(700μmol·mol^(-1)CO_(2)concentration and 22℃ambient temperature,EC),elevated CO_(2)concentration and warming(700μmol·mol^(-1)CO_(2)concentration and 26℃ambient temperature,EC+T),and control(400μmol·mol^(-1)CO_(2)concentration and22℃ambient temperature,CK).Two water conditions were set for each climate scenario as follows:adequate water supply(70%field capacity)and mild drought stress(50%field capacity).The responses of the activities and temperature sensitivity ofβ-glucosidase(βG),β-N-acetyl glucosidase(NAG),cellulase(CBH),andβ-xylosidase(βX)to elevated CO_(2)concentration and warming were analyzed.The results showed that the activities ofβG,NAG,CBH,andβX in the control group(CK)first increased and then decreased with an increase in incubation temperature under the condition of sufficient water supply,and the temperature at which enzyme activities were the highest was 25℃.At the optimum temperature(25℃),elevated CO_(2)concentration significantly decreased soilβG activity but had little inhibitory effect on the activities of soil NAG,CBH,andβX.The effect of the interaction between elevated CO_(2)concentration and warming was related to water conditions;specifically,the enzyme activities were inhibited under mild drought condition but no significant difference was observed under adequate water supply.In addition,elevated CO_(2)concentrations and warming significantly affected the temperature sensitivity(Q_(10))of soil enzyme activity at millet grain filling stage.The elevated CO_(2)concentration significantly increased Q_(10),whereas warming decreased Q_(10).Under sufficient water supply,warming counteracted the effect of elevated CO_(2)concentration on Q_(10),and the interaction between elevated CO_(2)concentration and warming had no significant effect on Q_(10).However,elevated CO_(2)concentration and warming had significant effects on Q_(10) under mild drought condition as follows:the interaction of CO_(2)concentration,temperature,and water content on Q_(10)was significant.In addition,the interaction between elevated CO_(2)concentration and mild drought had a significant effect on Q_(10),but there was no significant difference in the effect of elevated CO_(2)concentration and the interaction of the three factors.Moreover,redundancy analysis showed that Q_(10) was affected by environmental variables such as microbial biomass and soil nutrients.This study demonstrated that the effects of elevated CO_(2)concentration,warming,drought,and their interactions on soil enzyme activities and temperature sensitivity were complex and particularly,the elevated CO_(2)concentration inhibited the temperature sensitivity of soil enzymes and weakened the metabolic functions and stability of enzymes related to soil carbon and nitrogen cycling,which further affected the functional stability of the soil ecosystem.