Effects Of Carbon Addition On Catalytic Properties Of Enzymes And Structural Diversity Of Microbial Communities In Farmland Soil

Carbon source return as organic material is an effective way to maintain soil fertility,improve soil quality and increase soil microbial populations.By investigating the changes in soil enzyme activity,enzymatic reaction mechanism and bacterial community structure diversity after the addition of different carbon sources,the impact of carbon source addition on the fertility quality of farmland soils can be clarified from the perspective of soil microbiology.On the basis of previous studies on the fertility of black soils on farmland,three types of carbon sources（straw,biochar and nano carbon）were selected for field trials to study the effects of different carbon sources at different temperatures on soil enzyme activity,catalytic kinetics and thermodynamic characteristics of enzymatic reactions,and structural diversity of soil bacterial communities.In addition,the differences in response and temperature adaptation of soil enzymes and microorganisms to the addition of the three different types of carbon sources were compared to provide a scientific basis for agricultural production in the black soil region of Northeast China.The results were as follows:1.Carbon source,temperature and the interaction between them had significant effects on soil catalase,invertase,urease and phosphatase activities.Compared to the control,the three carbon sources all reduced soil catalase and urease activity.Invertase activity increased with straw addition and decreased with biochar and nanocarbon addition.Phosphatase activity increased with straw addition and decreased significantly with nanocarbon addition.In the temperature range of 15℃～55℃,the activities of soil catalase and phosphatase increased with increasing temperature in all treatments,while the activity of catalase and urease first increased and then decreased.2.The carbon source and temperature had significant effects on the kinetic parameters K_m,V_maxand K_aof catalase,invertase,urease and phosphatase.However,the interaction of the two factors had no effect on K_mand V_maxof catalase and K_aof phosphatase.Compared to the control,straw increased catalase K_m,invertase K_aand phosphatase V_max;and decreased the K_avalues of catalase,urease and phosphatase.Biochar reduced the V_maxand K_aof catalase,the V_maxof invertase,and the K_aof urease and phosphatase.Nano carbon increased K_mof soil catalase,urease and phosphatase but reduced the K_mof soil invertase,V_maxof four enzymes and K_aof catalase,urease and phosphatase.The K_mvalues of the three carbon sources added with increasing temperature showed no uniform patternin the temperature range of 15℃ to 55℃.As the temperature increased the V_maxand K_aof catalase and urease,the K_aof invertase and the V_maxof phosphatase increased and then decreased,with the maximum value at 25℃ or45℃.Invertase V_maxand phosphatase K_avalues gradually increased,with a maximum at55℃.3.The carbon source had a significant effect on the thermodynamic parameters ofΔG,ΔH andΔS for catalase,invertase,urease and phosphatase,while temperature and the interaction of the two factors only had a significant effect on theΔG values of the enzymes.Compared to the control,straw increased theΔG,ΔH andΔS of soil catalase,invertase and urease and decreased the three thermodynamic parameters of phosphatase.Biochar increased theΔG of soil catalase,invertase and urease.Nano carbon increased theΔG of the four soil enzymes as well as theΔH andΔS of phosphatases.In the temperature range of 15℃～55℃,theΔG of catalase,invertase,urease and phosphatase increased gradually with increasing temperature for each treatment,while other thermodynamic parameters did not change significantly.4.The results of the principal component analysis showed that soil enzyme activity,kinetic and thermodynamic parameters after the addition of different carbon sources were influenced by different soil physicochemical properties.After straw addition soil TC,AN and TN content were the main factors affecting the four enzymes’activity,kinetic and thermodynamic parameters.After biochar addition the TP and pH became the main factors affecting the enzyme activity and catalytic characteristics.After nano carbon addition AP became the main influencing factor.5.Three carbon source additions changed the structural diversity of the soil bacterial community and reduced the number of soil bacterial OTUs,Chao 1 index,Observed species index,and Shannon index.There was no change in the dominant soil phylum before and after carbon source application,all of which were Actinobacteria,Proteobacteria,Acidobacteria,and Chloroflexi.The addition of three carbon sources increased the relative abundance of Proteobacteria at the phylum level and Alphaproteobacteria,Betaproteobacteria,Actinobacteria,Gemmatimonadetes at the class level;it decreased the relative abundance of Acidobacteria,Chloroflexi,Subgroup6,Blastocatellia.The addition of carbon sources affected the inter-group differences in soil bacterial communities,in which straw and nanocarbon addition resulted in one and four differential species,however,biochar addition did not result in differential species.In the redundancy analysis,soil AP,TP,TN and TC contents were positively correlated with the soil bacterial community,and the straw and nano carbon additions were more different from the soil bacterial community in the control.