Effects Of Element Metering Ratio On Carbon Turnover In Paddy Soil And Its Regulation

Soil organic carbon cycling is controlled by soil microenvironment,substrate and microbe.The frequent redox alternation of paddy soil determines its unique carbon and nutrient cycling processes,but the nutrient content and its metrological coupling mechanism and regulatory mechanism closely related to the carbon cycle are not clear.Therefore,based on elemental metrology and eco-stoichiometry,¹³C isotope tracer technique is used to quantify the exogenous carbon mineralization and its priming effect under the different element metering ratio.Quantitative migration and distribution characteristics of quantitative carbon in soil carbon pool and the transformation of soil nutrient elements is useful for clarifying the relationship between soil carbon turnover and elemental metrology in paddy soil.Exploring the characteristics of key enzyme activities involved in soil C/N/P cycling is important to elucidate the mechanism of soil carbonization and transformation in paddy soil.Based on the multivariate statistical analysis method and the variables of soil physical and chemical factors under different element metering ratios,the mechanism of elemental eco-chemical metrology of soil carbon turnover was revealed.This study can provide scientific basis for deep understanding of carbon cycle of farmland ecosystem,strengthening soil nutrient management in paddy field,improving soil productivity and reducing greenhouse gas emissions.In this study,¹³C-labeled glucose was selected as a typical carbon source for paddy soil.Different levels of exogenous carbon were added based on soil microbial biomass carbon?MBC?,and the corresponding N,P and S nutrient elements stoichiometric ratio were added to study the responses of soil activated carbon to exogenous carbon addition and the elements metrological control mechanism of exogenous carbon turnover.The soil microbial biomass MBC was 440 mg·kg^-1.Two different levels of C addition were set:?Low amount of glucose addition?GL?:50%MBC,0.22 g C/kg soil;?High amount of glucose addition?GH?:50%MBC,2.2 g C/kg soil.The addition of N,P and S nutrient was based on microbial carbon utilization?CUE?and set as 0,0.1,0.3,0.5,0.6 gradients.They are added in the form of NH₄Cl,KH₂PO₄ and Ca₂SO₄ solution.The main experimental treatments were as follows:?Soil,?Soil+L_1-4,?Soil+H_1-4,?Soil+50%MBC Glucose-C+low nutrient element test group(Soil+GL_0-4),?Soil+500%MBC glucose-C+high nutrient element test group(Soil+GH_0-4).The main results are as follows:?1?Throughout the whole incubation period,glucose is mainly released in the form of CO₂ gas.Different carbon additions promoted the formation of CO₂,the higher the amount of exogenous carbon,the higher the cumulative mineralization rate of glucose-C.With the increase of the proportion of nutrient elements,the cumulative mineralization rate of glucose-C gradually increased.The content of glucose-C in the form of DOC in the aqueous solution is very small,almost zero;and the C content in SOC is relatively stable.The addition of low glucose?50%MBC glucose-C?resulted in a positive effect on the original organic matter of the soil,and the positive priming effect was gradually increased with the increase of the nutrient element ratio.The high glucose content?500%MBC glucose-C?has a negative effect on the original organic matter of the soil,the greater the amount of nutrient added,the stronger the negative priming effect.?2?Under the condition of low amount of exogenous carbon addition,the addition of nutrient elements increased the proportion of glucose-C rapid conversion carbon pool?a1?in the soil,up to 55%,thereby increasing the glucose-C mineralization rate.Nutrient element ratio and the proportion of rapidly changing carbon pool and mineralization rate of glucose-C showed a significant positive correlation.The addition of nutrient elements increased the glucose-C mineralization rate with high glucose-C addition,but decreasing the proportion of glucose-C rapidly converted carbon pool in soil,accounting for about 30%.The ratio of nutrient elements to glucose-C mineralization rate was positively correlated.But it was negatively correlated with the rapid conversion of carbon pool.?3?When the input of exogenous carbon was insufficient,the amount of N and P was limited,and the MBN and MBP were less in the soil.The excess of exogenous carbon and nutrient input greatly promoted the utilization of P and the increase of MBP.The results showed that the contents of MBC,MBN and MBP increased with the increase of elemental ratio,and the contents of MBC,MBN and MBP increased with the increase of elemental ratio.?4?Under the input of exogenous C and nutrient elements,the mineralization rate of glucose-C was negatively correlated with soil biomass.And the priming effect was positively correlated with soil microbial biomass.Under the input of low amount of carbon and nutrient elements,the glucose-C mineralization rate and the priming effect were negatively correlated with the related functional enzyme activities?4 main enzyme activities were test,including:??-cellobiohydrolase?CBH?,??-glucosidase?BG?,?acetyl-glucosaminidase?NAG?and?acid phosphatase?AP??.While,with the input of the excess carbon sources and nutrient elements,the priming effect showed a positive correlation with the enzyme activity involved in the C and N cycling.It was negatively correlated with the AP.The mineralization rate was negatively correlated with CBH,BG and NAG.C,N,P,S and other elements directly changed the soil physical and chemical characteristics,microbial biomass and key functional enzyme activity,but also feedback control of soil carbon turnover process.