Turnover Of The Organic Carbon In Paddy Soil With Different Microbial Activities

Carbon(C)cycle and C sequestration are regulated by soil environment,microbe and substrate.Rice paddy soil is a representative agricultural soil in China,it has strongly C sequestration capacity.However,the C sequestration potential of paddy soil under different physicochemical properties and microbial activities is different.The simple metabolites in the transformation process of glucose simulated organic matter(SOM)is used to quantify the turnover and distribution of exogenous C,to clarify the microbial response to soil carbon turnover in paddy fields.This study provide a scientific basis for agricultural input,enhance carbon sequestration potential and reduce greenhouse gas emissions.In this study,three levels of different microbial biomass carbon(MBC)content of subtropical typical paddy soils were selected as different microbial activity soils.13C-glucose was used as fresh organic matter,six glucose levels according to the MBC percentage in each soil:control,0%,50%,100%,300%,and 500%of MBC with three replicates.Under the exogenous C on paddy soils with different microbial actives,and different carbon supply gradients on paddy soils,we discussed the coupling relationship between soil carbon turnover,microbial process and response of N,P nutrient elements.The main results were as follows:(1)Exogenous C stimulated the release of CO2.The source of CO2 changed from glucose to soil organic matter with the training time extended.The CO2 from soil organic matter decreased gradually with the addition of glucose.However,the cumulative mineralization rate increased,and the growth rate of the low MBC soil was greater than that of the high MBC soil.The addition of glucose promoted the proportion of glucose-C rapid conversion C pool in the low and middle MBC soil.But the C stocks were still dominated by slow conversion C pool,whereas the high MBC soil was opposite.The positive priming effect of the middle MBC soil was stronger than that of in the low MBC soil,and the negative priming effect of the high MBC soil increased with the addition of glucose.(2)The glucose-C fate in paddy soils was 1)mineralized to CO2;2)remained in soil solution as DOC and 3)incorporated into SOC.In the early incubation stage,the exogenous C existed mainly in the form of SOC,and the rate of SOC in the high MBC soil was larger than that in the low MBC soil.The proportion of 13CO2 in the low MBC soil and the content of DOC in soil solution in middle soil was highest,about 12.9%-16.2%and 19.3%-29.4%,respectively.During the posterior period of incubation,exogenous C was mainly mineralized to CO2,meanwhile,remained in soil solution as DOC was almost none.With the addition of glucose,the recovery of ’3C in the low and the middle MBC soil increased gradually,and the recovery in the high MBC soil decreased gradually.The content of MBC in soil increased first and then decreased,and the content in the high MBC soil was higher than that in the low MBC soil.(3)Exogenous C changed soil pH,the distribution of N,P,and promoted the decomposition of original organic matter.The soil N and P were mainly existed as NH4+-N and Olsen-P in the soil.When the external carbon input was insufficient,soil MBN and MBP contents were relatively low.Sufficient exogenous carbon input promotes microbial utilization of N and P,the MBN and MBP increased.Excessive external carbon input reduces the MBN and MBP.The amount of MBN in the high MBC soil was higher than that of the other two soils.Different paddy soils with different microbial activities have different optimal glucose addition ratios.(4)In the early incubation stage,the activity of β-Glu decreased gradually with the addition of glucose,while,the activity of NAG and AP fluctuated greatly.Then,the enzyme activity increased gradually with the training time extended.The carbon substrate use efficiency was higher in the high MBC soil,lower in the low MBC soil in this treament.The utilization rate of three carboxylic acid C sources(formic acid,eugenic acid,succinic acid)was low in three paddy soils.There had a significant positive linear between the respiratory quotient and glucose in three paddy soils in the early incubation stage.At the end of incubation time,high addition ratio increased the respiration entropy of the low MBC soil,but decreased the respiration entropy of the high MBC soil.(5)Under the input of exogenous C,the MBC/MBP was positively correlated with MBC/MBP,the soil mineralization rate and PE were positively correlated with pH and MBP in this treatment.There had a stronger correlation with the soil NH4+-N and MBP when the soil MBC content was higher,meanwhile,the soil was more susceptible to the control of N,P nutrient elements.