Effects Of Straw And Nitrogen Addition On Characteristics Of Phosphorus Transformation In Long-Term Straw-Returned Soils

Phosphorus is an indispensable nutrient in agricultural production,the utilization rate of phosphorus fertilizer is low,and most of the phosphorus is accumulated in the soil.In soil,the availability of phosphorus depends on its existing form and transformation dynamics,and the latter is mainly driven by microorganisms.Long-term straw returning to the field causes changes in soil phosphorus forms and microbial communities.However,the effect of Straw and nitrogen addition on the characteristics of soil phosphorus turnover and its related microbial driving mechanism under the background of long-term straw returning is not clear.In this study,we selected soil that had received straw returning at the rates of 0%,33%,67%,and 100%for 15 years as the research objects and set up four treatments,including control,single nitrogen application,single straw application,and mixed straw and nitrogen application.The indoor culture experiment was carried out at 25℃for 120days.The related indexes of carbon,nitrogen and phosphorus and the changes of soil enzyme and microbial community composition were analyzed.To explore the effect of straw and nitrogen addition on soil phosphorus transformation under long-term straw returning treatments,and analyze its microbial driving mechanism.The main results are as follows:（1）Long-term straw returning increased the content of soil Olsen phosphorus and changed the proportion of soil labile phosphorus.Compared with the non-returning soil,the soil Olsen phosphorus content of straw returning soil increased significantly,of which 33%straw returning soil had the highest Olsen phosphorus,which was 5.01%higher than that of non-returning soil.In addition,long-term straw returning significantly promoted soil phosphorus turnover.In the soil with 33%and67%of straw returning,labile phosphorus components increased by 4.55%and19.67%,while non-labile phosphorus components decreased by 5.90%and 24.15%.（2）Straw and nitrogen addition significantly increased the content of Olsen and labile phosphorus fractions in the soil.The Olsen phosphorus content of the soils differed significantly（P<0.05）between the different straw returns during the incubation period.The nitrogen application alone treatment significantly increased P_SOLand P_M3content,with the largest increase of 5.25%in the labile phosphorus fraction in 67%straw-returned soil.The straw application alone treatment increased the labile phosphorus by 16.3%,12.42%,15.21%and 15.27%in the four soil samples,respectively.The straw with nitrogen application treatment increased the microbial biomass phosphorus content.（3）Straw and nitrogen addition had significant effects on long-term straw-returned soil enzyme activity,with significantly higher phosphatase activity in the nitrogen alone,straw alone,and straw with nitrogen treatments than in the control.The activity of acid phosphatase was positively correlated with that ofβ-glucosidase and N-acetyl-β-D-glucosaminidase（P<0.05）.Carbon and nitrogen converting enzyme could indirectly regulate soil phosphorus transformation by affecting acid phosphatase.The results of structural equation model also showed that the addition of straw and nitrogen could also directly affect the content of soil Olsen phosphorus and labile phosphorus by regulating carbon-nitrogen invertase.（4）The number and diversity of microorganisms in long-term straw returning soil were significantly increased by addition of straw and nitrogen.Bacterial community diversity was the direct factor of soil Olsen phosphorus,and it was positively correlated with soil Olsen phosphorus（P<0.001）.Straw and nitrogen can regulate soil phosphorus turnover by directly or indirectly affecting the content of microbial biomass carbon and phosphorus.Straw and nitrogen treatments significantly changed the relative abundance of carbon and nitrogen-related microorganisms,and then indirectly affected soil phosphorus transformation.In summary,the present study found that long-term straw return to the field prompted changes in the ratio of soil phosphorus fraction,revealed that the addition of straw and nitrogen affected the changes of soil phosphorus fraction and related microbiota,and explored the effects of soil microorganisms on soil phosphorus transformation under the conditions of straw and nitrogen addition.The results can provide more theoretical support for the in-depth study of the regulatory role of microorganisms on soil phosphorus transformation and the improvement of soil cumulative phosphorus utilization efficiency.