玉米秸秆添加对土壤碳氮周转相关酶活性动态的影响

Effects of Maize ResidueAmendment on the Dynamics of Enzyme Activities Related with Soil Carbon and Nitrogen Turnover

玉米秸秆是旱地农田重要的可利用资源,归还的秸秆通过不断分解可维持或提高土壤有机碳的积累。了解玉米秸秆分解过程中土壤碳氮周转相关酶活性动态变化,阐明外源碳输入对土壤碳氮周转及有机质形成的影响具有重要意义。本研究采用室内恒温培养法(360天),研究添加量分别为0(CK)、5 mg g^-1(T1)、10 mg g^-1(T2)的玉米秸秆对土壤有机碳、总氮含量和微生物量的影响以及对土壤β-葡萄糖苷酶(βG)、纤维二糖酶(CB)、β-N-乙酰氨基葡萄糖苷酶(NAG)、亮氨酸氨基肽酶(LAP)、多酚氧化酶(PPO)和过氧化物酶(PER)活性的动态影响。研究结果表明,秸秆分解及其对土壤酶和物质转化的调控分为特征各异的三个阶段。土壤中易分解组分的分解主要发生在培养前90天(第一阶段),此阶段内各处理土壤有机碳、总氮含量均显著降低,6种土壤酶活性均较低。随着培养时间的增加,土壤βG和CB活性无显著变化,而木质素酶活性缓慢升高,表明木质素与活性较高的组分分解可能存在共代谢作用。各处理中LAP活性在30天时升高而后降低,表明当氮需求量增加时,可通过蛋白质的分解提供可利用氮。在第二阶段(90~240天),6种土壤酶活性均显著升高且极显著正相关,表明水解酶和氧化酶通过协同作用维持土壤碳氮供需平衡。在培养的第三阶段(240~360天),除PPO外其它5种酶活性均显著降低,说明微生物可能主要依靠分解酚类物质维持自身的代谢。在整个培养期间,与对照处理相比,秸秆添加后可利用底物增多,土壤微生物量提高3~57%(T1)和3~146%(T2)。秸秆添加使水解酶(βG,CB,NAG,LAP)活性升高,但使氧化酶(PPO,PER)活性降低,表明秸秆添加可能减少了微生物对稳定性底物的利用,促进了木质素等难分解组分积累、使土壤有机碳含量提高。本研究为深入理解秸秆生物降解、提高土壤有机碳积累机制提供了新见解。

Maize residue is an important available resource in a rainfed farmland.The application of residue could improve the accumulation of soil organic carbon(C)through continuous decomposition.Therefore,it is important to understand the temporal changes of enzyme activities related with soil C and nitrogen(N)turnover during the decomposition of maize residue,which could further clarify the potential mechanism of soil C and N turnover and soil organic matter formation after the exogenous C application.The influences of maize residue at the ratio of 0(CK),5 mg g^-1(T1),10 mg g^-1(T2)on soil organic C,total N,microbial biomass and the temporal changes of soilβ-glucosidase(βG),cellobiohydrolase(CB),β-N-acetylglucosaminidase(NAG),leucine aminopeptidase(LAP),polyphenol oxidase(PPO)and peroxidase(PER)activities were investigated in a laboratory incubation experiment of 360 days.The results showed that the decomposition of labile components in soil and residue were mainly occurred in the first 90 days of residue application.The contents of soil organic C and total N and six soil enzymes activities were significantly reduced.With the increase of incubation time,the activities ofβG and CB in soil were not changed significantly,while the activities of lignin enzyme were increased slowly,indicating that lignin and the labile component decomposition may have a co-metabolic effect.The LAP activities increased at the 30 th day and then decreased gradually,implying that protein decomposition could provide available N under more soil N requirement.During the90-240 days,the six enzymes activities was significantly increased and positively correlated with each other,implying that hydrolase and oxidase would maintain the balance between supply and demand of soil C and N.During the 240-360 days of incubation,the enzymes(except PPO)activities decreased significantly,indicating that the microorganisms may maintain their metabolism mainly by consuming phenolic substances.Throughout the incubation period,compared with the CK,maize residue addition enhanced soil microbial biomass by 3-57%(T1)and 3-146%(T2)due to the increase of available substrates.The residue amendment increased the hydrolase activities,but decreased the oxidase activities,indicating that residue application reduced the utilization of stable substrates by microorganisms,and thus promoted the accumulation of recalcitrance components(e.g.lignin)and soil organic C.This study provided a new insight for understanding the mechanism of straw decomposition and soil organic C accumulation.