【摘要】 外源碳会改变土壤有机质的转化以及土壤微生物的活性,不同水平的易利用有机碳在稻田土壤中转化与分配的微生物响应特征尚不明确.为阐释外源碳周转过程中的微生物响应特征,选取葡萄糖为典型易利用外源碳,采用13C稳定同位素标记技术,在室内模拟培养实验,基于土壤微生物生物量碳(MBC)设置不同水平葡萄糖碳(0×MBC、0. 5×MBC、1×MBC、3×MBC和5×MBC共5个MBC倍数梯度水平),明确其转化与分配规律;并利用96微孔酶标板荧光分析法,测定参与土壤碳转化过程关键酶纤维二糖水解酶(CBH)和β-葡萄糖苷酶(β-Glu)活性.结果表明,培养2 d时,葡萄糖碳(13C)占可溶性有机碳(13C-DOC)和土壤有机碳(13C-SOC)的比例与其添加量成显著正相关;向13C-MBC的分配在3×MBC处理时达到最大值(18. 96 mg·kg-1),随后降低;13C分配率主要与MBC、Olsen-P和DOC存在显著正相关关系. 60 d时,土壤13C-DOC、13C-MBC和13C-SOC显著下降,分别小于或等于0. 02、2和10 mg·kg-1;与CK相比,添加葡萄糖后CBH酶活性显著提高,其中3×MBC处理提高了22. 6倍,显著高于其它处理(P <0. 05);高量葡萄糖(3×MBC和5×MBC)添加促进了β-Glu酶活性,但促进效果随葡萄糖添加量的增加而减少; NH+4-N、p H、β-Glu和CBH成为13C分配率的主要影响因子.综上,外源碳向土壤有机碳的转化随添加量的增加而增加,改变了土壤酶活性,但微生物对外源碳的利用可能存在一个饱和阈值,饱和阈值之内,有机质的转化速率与添加量成正比;超出饱和阈值,有机质的转化速率反而变慢.因此,适量地添加外源碳有利于提高稻田土壤有机碳,优化作物生长环境质量.更多还原

【Abstract】 The turnover of soil organic carbon( SOC) and the activity of soil microbes can be influenced by exogenous carbon.However,microbial response characteristics of the transformation and distribution of available organic carbon under different levels remain unclear in paddy soils.13 C-labeled glucose was used as a typical available exogenous carbon to simulate indoor culture experiments added at different levels of soil microbial biomass carbon( MBC)( 0 × MBC,0. 5 × MBC,1 × MBC,3 × MBC,and 5 ×MBC) to reveal the process of C-transformation and distribution. The characteristics of microbial response in the process of exogenous carbon turnover was also monitored. The 96-well microplate fluorescence analysis was adopted to determine the activities of cellobiose hydrolase( CBH) and β-glucosidase( β-Glu). The results showed that,in 2 d of incubation,the ratio of labeled glucose carbon to dissolved organic carbon(13 C-DOC/DOC) or to SOC(13 C-SOC/SOC) was positively correlated with the amount of glucose added. The incorporation of glucose C(13 C) into MBC reached the highest value( 18. 96 mg·kg-1) at 3 × MBC treatment but decreased thereafter.The13 C allocation rate was mainly positively correlated with MBC,Olsen-P,and DOC. At 60 d,13 C-DOC,13 C-MBC,and13 C-SOC decreased significantly to less than 0. 02 mg·kg-1,2 mg·kg-1,and 10 mg·kg-1 in soil,and it was positively correlated with the amount of glucose added. Compared with CK,CBH enzyme activity increased significantly after the addition of glucose,and for the 3× MBC treatment it was increased by 22. 6 times,which was significantly higher than those of other treatments( P < 0. 05). However,β-Glu enzyme activity increased only in the 3 × MBC and 5 × MBC treatments,wherein it decreased with increasing amounts of addedglucose. NH+4-N,p H,β-Glu,and CBH were the primary factors affecting the distribution rate of13 C. In conclusion,the conversion of exogenous carbon to SOC increased with increased amounts of added organic carbon. This changed the activity of soil enzymes;however,microbial utilization of exogenous carbon may have a saturation threshold. Within the saturation threshold,the conversion rate of organic matter was directly proportional to the amount of added organic matter. When the saturation threshold was exceeded,the conversion rate of organic matter decreased. Therefore,the appropriate addition of exogenous carbon is beneficial,as it can increase SOC in rice fields and improve the quality of the crop growth environment.更多还原