Effect Of Long-term Fertilization On Soil Organic Carbon Priming Effect And Carbon Cycling-Related Functional Genes In Dryland Farming System

Soil organic carbon priming effect refers to the phenomenon that the input of exogenous organic carbon will cause the decomposition rate of soil original organic matter to change.Studying the generation mechanism of soil organic carbon priming effect and its microbial action mechanism will help to deepen the understanding of soil carbon cycle process and mechanism.Based on a 35-year long-term fertilization experiment,combined with ¹³C stable isotope labeling technology,this study investigated the effects of long-term nitrogen fertilizer application（N）,organic fertilizer application（M）,nitrogen and organic fertilizer combined application（NM）and control treatment（CK）on soil organic carbon and its active fractions in winter wheat field soil and the mechnism of soil organic carbon priming effect to long-term fertilization.Finally,soil microbial metagenomics analysis method was used to study the influence mechanism of soil carbon function genes and species on the priming effect under different fertilization conditions.The main results achieved are as follows:（1）After adding ¹³C-labeled glucose to the soil treated with long-term fertilization,the four soil treatments of CK,N,M and NM all showed a positive priming effect.During the cultivation process,the soil carbon priming effect rate gradually decreased and tended to be stable as the cultivation time went on.After the cultivation,the soil carbon priming effect of the four treatments were CK>N>M>NM.Compared with CK,the priming effect rates of N,M,and NM treatments were reduced by 9.49%,11.41%,and 17.05%,respectively.It indicating that the combined application of nitrogen fertilizer and organic fertilizer would reduce the priming effect of soil organic carbon and promote soil carbon sequestration.（2）Linear regression analysis of soil carbon composition and excitation effect showed that particulate organic carbon and potentially mineralized carbon were significantly correlated with excitation effect,and the priming effect decreased with the increase of particulate organic carbon and potential mineralized carbon.Linear regression analysis of soil carbon components and priming intensity showed that the intensity of priming effect weakened with the increase of the contents of the four carbon components,but there was no significant difference.（3）The correlation analysis of soil organic carbon priming effect,carbon components and nine types of functional genes showed that the abundance of soil carbon priming effect and easily decomposable carbon genes（monosaccharide,disaccharide,cellulose,aminosugar decomposition genes）under M treatment was significantly related.Soil organic carbon in CK treatment was significantly negatively correlated with the abundance of hemicellulose decomposition genes,but not after fertilization;particulate organic carbon in each treatment was not correlated with nine major genes;potential carbon mineralization was significantly negatively correlated with monosaccharide decomposition genes in CK treatment,and significantly positively correlated with lipid decomposition genes in M treatment;CK treatment microbial biomass carbon was significantly positively correlated with lignin decomposition genes,while M and NM treatments microbial biomass carbon was negatively correlated with lignin decomposition genes.（4）Random forest model analysis showed that bgl B,rha A,lig B,ysi A,fad R,yfa W and pdh R were the key genes affecting the priming effect of soil organic carbon.The results of topological network analysis showed that Actinobacteria and Chloroflexi were the two dominant bacterial groups in the process of soil organic carbon excitation.Compared with CK,M and NM treatments promoted the life activity of Actinobacteria,while inhibited the activity of Chloroflexi.On the whole,long-term application of organic fertilizer can effectively increase soil carbon content in winter wheat field.Long-term nitrogen fertilizer and organic fertilizer combined application soil priming effect is weaker than other fertilization treatments in response to exogenous carbon,which is more conducive to soil fertility and soil carbon sequestration.