Characteristics Of Soil Lignin Degrading Enzymes And Their Relationship With Soil Physical And Chemical Properties In Water-level-fluctuating Zone Of Danjiangkou Reservoir

As an integral part of the ecosystem in the reservoir area,the Water-level-fluctuating zone plays an important role in the source and sink of soil organic matter,the interception of non-point source pollutants and the improvement of water quality.Lignin degrading enzymes,mainly lignin peroxidase(LiP),manganese peroxidase(MnP)and laccase(Lac),participate in the decomposition of phenols,non phenols and other substances to release CO2 and other greenhouse gases,and produce a large number of organic acids and other substances,which directly or indirectly affect a series of biochemical reactions in soil.The existence of lignin degrading enzymes may lead to the transformation of source sink functions,affecting soil,water and environment.Therefore,this study selected the soil in the Water-level-fluctuating zone of Danjiangkou Reservoir as the research object.By measuring the activity,kinetic and thermodynamic parameters of LiP,MnP and Lac,as well as the physical and chemical properties of the soil,it discussed the characteristics of soil enzymes,clarified the relationship between the characteristic values of soil enzymes and the physical and chemical properties of the soil,revealed the reaction rate of soil enzymes in the drawdown zone and its influencing factors,and provided an important basis for the geochemical cycle of global carbon.The main conclusions are as follows:(1)The activities of LiP,MnP and Lac in the Water-level-fluctuating zone were higher than those in the Non-water-level-fluctuating zone,and SWC significantly affected the activities of these three enzymes.Further regulation path analysis showed that Fe(II)was the main factor affecting LiP activity;Mn(II)is the main factor affecting the activity of MnP;C/N and SWC affect Lac activity.(2)There are different changes in the dynamic characteristics of enzymes in the soil of the Water-level-fluctuating zone and the soil of the Non-water-level-fluctuating zone,which reflect the characteristics of the enzyme content,the difficulty of the formation of enzyme substrate complex,the speed of enzymatic reaction and so on.The maximum reaction rate(Vmax)of the three enzymes in the drawdown zone was as follows:LiP>MnP>Lac;Michaelis constant(Km)is expressed as Lac>LiP>MnP;The overall catalytic efficiency(Vmax/Km)is MnP>LiP>Lac.The kinetic parameters of the three enzymes were related to the physicochemical properties of SWC and high iron(Fe(Ⅲ)).The activities of the three enzymes increased with the increase of temperature and substrate concentration.The responses of the dynamic parameters of LiP,MnP and Lac to temperature are as follows:Vmax increases with the increase of culture temperature;Km fluctuates up and down with the change of temperature;Vmax/Km increases or remains unchanged with the increase of temperature(3)The Q10 of soil LiP,MnP and Lac kinetic parameters in the Water-level-fluctuating zone to temperature is mainly as follows:Qio of soil enzyme Vmax decreases with the increase of temperature;Q10 of Km increases or decreases with the increase of temperature;Qio of Vmax/Km increases with the increase of temperature.Qio of three enzyme kinetic parameters in soil is related to physical and chemical properties such as Fe(Ⅲ),pH and Mn(Ⅱ).(4)The response of the thermodynamic parameters of LiP,MnP and Lac in the Water-level-fluctuating zone to temperature is mainly as follows:ΔH and ΔS decrease with the increase of temperature,and ΔG increases with the increase of temperature,but the increase is small.The Ea of three enzymes in soil is related to physical and chemical properties such as C/N.