Root exudates are one of the main sources of exogenous carbon in paddy soils.At present,the research on root exudates and their induced soil ecological effects in paddy soils mainly focuses on the input of rhizosphere carbon(C),but there are few studies on the coupling relationship between rhizosphere carbon and nitrogen,phosphorus and its impact on soil ecological functions,which greatly restricts the research.We have a deep understanding of the root-soil interaction mechanism in paddy fields.Based on13C isotope tracer technique and element metrology knowledge,this paper analyzed the turnover of root exudates and the regulation mechanism of element measurement ratio under different nutrient measurement ratios in paddy soil,which provided theoretical basis for the study of carbon sequestration potential and greenhouse gas emission reduction in paddy ecosystem.In this study,a typical paddy soil in subtropical zone was selected as the object of study.Eco-element metrology and isotope tracer techniques were used to synthesize the carbon source of simulated root exudates composed of glucose,oxalic acid and alanine,and13C labeling was carried out.At the same time,two ways of adding(one addition and continuous addition)were set up.)The experimental treatments were as follows:1 addition treatment(PI):control(soil+water);soil+simulated root exudates+nutrient solution C:N:P(0)(where C:N:P(0)refers to the ratio of C:N:P in nutrient solution when the microbial UE is0);soil+simulated root nutrient solution C:N:P(0);C:N:P(0.2);soil+simulated root exudates+nutrient solution C:N:P(0.4);soil+simulated root exudates+nutrient solution C:N:P(0.6);continuous addition treatment(CI):soil+simulated root exudates+nutrient solution C:N:P(0);soil+simulated root exudates+nutrient solution C:N:P(0.2);soil+simulated root exudates+nutrient solution C:N:P(0.2);soil+simulated root exudates+simulated root nutrient solution C:N:P(0.2);Secretion+nutrient solution C:N:P(0.4);soil+simulated root exudate+nutrient solution C:N:P(0.6).The results of this study are as follows:(1)The input of simulated root exudates increased the mineralization of soil carbon;and with the increase of nutrient element measurement ratio,the cumulative mineralization rate of soil endogenous and exogenous carbon gradually decreased;the cumulative release and mineralization rate of soil endogenous carbon in continuous addition treatment were significantly higher than that in single addition treatment.In a single addition treatment,the increase of nutrient element measurement ratio led to a 16%decrease in the proportion of rapidly converted carbon pools in soil and a corresponding decrease in the mineralization rate of exogenous carbon.In a continuous addition treatment,the proportion of rapidly converted carbon pools in soil increased by 22.5%with the increase of nutrient element measurement ratio,but the mineralization rate of exogenous carbon decreased accordingly.The chemical conversion rate decreased gradually.(2)The addition of simulated root exudates had significant effects on soil MBC,MBN and MBP,and promoted the contents of MBC,MBN and MBP.The change of nutrient element measurement ratio significantly affected the transformation of C,N and P in soil.With the increase of element measurement ratio,the level of nutrient assimilation and absorption by microorganisms increased synchronously,and the corresponding MBC,MBN and MBP contents increased significantly.Compared with one-time nutrient input,continuous nutrient addition can improve the continuity of microbial utilization of C,N and P elements,so that the contents of MBC,MBN and MBP in soil treated with continuous nutrient addition are significantly higher than those treated with one-time nutrient addition.(3)With the addition of simulated root exudates and nutrient elements,the microbial biomass was negatively correlated with the internal and external carbon mineralization rates of CO2 generated by mineralization,but positively correlated with the internal and external carbon mineralization rates of CH4 generated by mineralization.In one-time addition treatment,soil enzyme activity(BG,NAG,AP)was negatively correlated with the mineralization rate of endogenous and exogenous carbon,and positively correlated with the mineralization rate of endogenous and exogenous carbon.In continuous addition treatment,the mineralization rate of endogenous and exogenous carbon was positively correlated with the activity of NAG.There was a negative correlation with BG and AP.There was a positive correlation between endogenous and exogenous carbon mineralization and soil enzyme activities(BG,NAG,AP).(4)The input of simulated root exudates and nutrient elements affected the C:N:P ratio of soil physicochemical and microbial biomass,thus affecting the mineralization of soil carbon.There was a positive correlation between the mineralization of endogenous and exogenous carbon and the change of C:P and C:N ratio.The input of C,N,P and other elements directly changed soil physical and chemical characteristics,microbial biomass and key functional enzymes,and at the same time feedback regulated the turnover process of soil exogenous carbon. |