不同大气CO2浓度升高处理对水稻秸秆在后茬冬小麦田中分解特性的影响

为研究大气CO₂浓度逐渐增加和稳定高浓度处理对水稻秸秆在后茬冬小麦田土壤中分解特性的影响，进行田间试验，设置3个浓度水平——背景大气CO₂浓度(CK)、每个生长季CO₂浓度比CK逐渐增加40 μmol/mol(T1)、每个生长季CO₂浓度均比CK高200 μmol/mol(T2)，处于上述3个浓度水平下连续3个生长季的水稻秸秆处理编号分别用CK-OTC、T1-OTC、T2-OTC表示，第3个生长季T1-OTC的CO₂浓度为120 μmol/mol，3个生长季中前两个生长季处于开顶箱(OTC)外且第3个生长季处于OTC内的处理分别表示为CK、T1、T2.将不同处理下的水稻秸秆埋入麦田土壤中，于填埋后30、60、84、119、149 d测定剩余秸秆的质量以及总碳(TC)、总氮(TN)含量.结果表明:填埋后30 d不同处理下秸秆的分解率为33.2%~38.2%，至149 d填埋结束，不同处理下秸秆的分解率为57.3%~60.3%.填埋试验后期(填埋后84、119、149 d)的秸秆分解率与粗纤维含量之间存在显著(P < 0.05)或极显著(P < 0.01)相关关系.T1、T2处理下水稻秸秆在分解过程中的TC含量与CK无显著(P>0.05)差异，而OTC-T1处理下水稻秸秆在整个分解阶段的TC含量显著(P < 0.05)高于CK，且在填埋后60~119 d这一阶段T2处理下TC含量与OTC-CK处理之间存在边缘显著(0.05 < P < 0.10)差异.所有处理下的TC含量在填埋后比填埋前均明显降低，特别是对于TN含量而言，大部分处理下TN含量均随时间的线性增加程度达到极显著(P < 0.01)水平，C/N均在分解过程中随时间呈线性降低趋势(P < 0.05).研究显示，一个生长季尺度上CO₂浓度的升高会提高秸秆分解率，秸秆分解过程中TC分解速率比TN快，从而造成C/N下降. 

Effects of Elevated CO2 Concentration on Decomposition Properties of Rice Straw in Following Winter Wheat Cropland

In order to investigate the effects of elevated CO₂ concentration on the decomposition properties of rice straw in the following cropland, field experiments were performed. There were three CO₂ concentration levels, including ambient atmospheric CO₂ concentration (CK), elevated atmospheric CO₂ concentration with 40 μmol/mol higher during each of the following growing season than that during the previous season (T1), and elevated atmospheric CO₂ concentration with 200 μmol/mol higher than ambient atmospheric CO₂ concentration during each of the growing season (T2). In the three consecutive growing seasons, the codes of the treatments that were under the above three CO₂ concentrations were represented by CK-OTC, T1-OTC, and T2-OTC, respectively. The CO₂ concentration in the third growing season in T1-OTC was 120 μmol/mol. The codes of the treatments that were under the above three CO₂ concentrations only during third growing seasons rather than the first two growing seasons were represented by CK, T1, and T2, respectively. The rice straws under the different atmospheric CO₂ concentration treatments were embedded into the soil of the winter wheat cropland. The straw quality and total carbon (TC) and total nitrogen (TN) contents of straw were determined after 30, 60, 84, 119 and 149 d of embedding. The results indicated that the decomposition rates of straw varied from 33.2% to 38.2% after 30 d of embedding, while those varied from 57.3% to 60.3% after 149 d of embedding. The decomposition rates of straw were significantly (P < 0.05) or highly significantly (P < 0.01) correlated with hemicellulose during the last period of embedding experiments (84, 119, and 149 d after embedding). There was no significant difference in the TC content of rice straw between the elevated CO₂ concentration (200 μmol/mol) treatments (T1 and T2) and CK during the decomposition processes. The TC content of rice straw in the T2-OTC plot was significantly higher than that in the CK plot during the whole experimental period. Moreover, there was marginally significant (0.05 < P < 0.10) difference in the TC content between T2 and CK-OTC after 60 to 119 d of embedding. The TC content under all treatments decreased after embedding compared with that before embedding. The TN content increased significantly (P < 0.05) and linearly with the increase of embedding time, and most regression lines were highly significant (P < 0.01). The C/N decreased significantly (P < 0.05) and linearly with the increase of embedding time. It was concluded that the elevated CO₂ concentration during a growing season increased the straw decomposition rate. The decomposition rate of TC was greater than that of TN during the straw decomposition period, resulting in the decrease in the C/N.