Effects Of Zinc Application On Transformation Of Nitrogen And Phosphorus Forms And Microbial Community In Rice Rhizosphere Soil

Rice is one of the main food crops in our country.The increasing and stable production of rice is of great significance to our national food security.Nitrogen and phosphorus are not only the essential macronutrients for crop growth,but also the limiting factors for yield production and quality.In agricultural production,a large amount of nitrogen and phosphorus fertilizers are often used to ensure high yield of crops.Previous studies have shown that the combined application of zinc fertilizer with nitrogen and phosphorus is beneficial to rice growth and yield production.However,the effect as well as the mechanism of zinc application on the transformation of nitrogen and phosphorus in rice rhizosphere soil are not yet clear.In this study,the indica hybrid rice Guangliangyou 35 was used as the research material,and the effects of zinc application on the transformation of nitrogen and phosphorus in rice rhizosphere soil under different nitrogen and phosphorus application levels were analyzed through the pot experiment.The bacterial and fungal community structure in the rhizosphere soil and the key enzyme activities and gene expression levels of nitrogen and phosphorus form transformation were analyzed.The mechanism of zinc application promoting nitrogen and phosphorus form transformation in rice rhizosphere soil was revealed.The main findings are as follows:1.The effect and mechanism of zinc on nitrogen transformation in rice rhizosphere soil under the combined application of nitrogen and zincUnder normal nitrogen level,Zn application significantly increased the plant height,above-ground dry weight and above-ground nitrogen and phosphorus accumulation of Guangliangyou 35,and also significantly increased the content of alkali-hydrolyzed nitrogen,available phosphorus and ion-exchanged nitrogen,while significantly reduced the content of non-transformed nitrogen in the rhizosphere soil.After zinc application,the activities of protease,cellulase and dehydrogenase in the rhizosphere soil increased significantly,and the activity of catalase decreased significantly;the diversity of bacteria and fungi increased,and bacterial and fungal communities changed.Among them,the relative abundances of phosphorus-dissolving bacteria,such as Sphingomonas,Flavisolibacter,and Gemmatimonas,as well as the genera Subgroup＿6 and Subgroup＿7 that decompose animal and plant residues increased,while the relative abundances of nitrogen-fixation-related Ramlibacter and nitrosation-related Ellin6067 decreased.The relative abundance of pathogenic fungi such as Gaeumannomyces,Alternaria and Curvularia decreased,and the relative abundance of saprophytic fungi such as Ascobolus increased.The results of gene expression level detection showed that under normal nitrogen level,the expression levels of Nap A,nir S,nor B,nrf A,amo A,pho D,pqqc,ppk were significantly increased,while the expression levels of nxr B,nif H were significantly decreased after zinc application.Under the high nitrogen level,the promoting effect of zinc application on Guangliangyou 35 was inhibited.The content of nitrogen and available phosphorus in the rhizosphere soil was not significantly changed,the increasing of dehydrogenase activity became slightly,but the sucrase activity increased significantly.Zinc fertilization still improved rhizosphere soil bacterial and fungal diversity at high nitrogen levels,but bacterial communities altered differently.After zinc application,the relative abundances of phosphorolytic bacteria such as Sphingomonas,Flavisolibacter and Gemmatimonas;azotobacter Ramlibacter and nitrosobacter Ellin6067 decreased,and the relative abundances of Subgroup＿6 and Subgroup＿7bacteria that decomposed animal and plant residues increased.The relative abundance of pathogenic fungi decreased and the relative abundance of saprophytes increased.The results of gene expression level detection showed that under high nitrogen level,the expression levels of Nar G,nxr B,nif H,pho C were significantly increased,while the expression levels of nrf A,pqqc were significantly decreased after zinc application.2.The effect and mechanism of zinc on phosphorus transformation in rice rhizosphere soil under combined application of phosphorus and zincUnder normal phosphorus level,Zn application increased the nitrogen content in the shoot of Guangliangyou 35,the content of available phosphorus and occluded phosphorus,the activity of acid phosphatase in the rhizosphere soil.The diversity of bacteria and fungi in the rhizosphere soil were not significant changed,but the community composition was significantly altered.After zinc application,the relative abundances of nitrosifying bacteria Ellin6067 and rhizobia AllorhizobiumNeorhizobium-Pararhizobium-Rhizobium decreased,while the relative abundances of nitrogen-fixing bacteria Ramlibacter,denitrifying bacteria Noviherbaspirillum,phosphorus-dissolving bacteria Sphingomonas,Flavisolibacter,Gemmatirosa and anaerobic slime bacteria Anaeromyxobacter increased.The relative abundance of pathogenic fungal genera such as Curvularia and Fusarium decreased.Under high phosphorus level,application of zinc would have an antagonistic effect,and the plant height of Guangliangyou 35 decreased significantly.Although the nitrogen content in the shoots still increased,the zinc content and absorption amount decreased significantly.There was no significant difference in the various forms of phosphorus in the rhizosphere soil.The increase of ion-exchanged zinc was significantly higher than the normal phosphorus level,but the increase of oxidizable and reducible zinc decreased,and the activities of protease,dehydrogenase and cellulase increased significantly.After Zn application,the diversity of bacteria and fungi in the rice rhizosphere soil did not change significantly,but the community composition changed significantly,among which the relative abundance of some phosphorus-solubilizing bacteria and nitrogen-fixing bacteria Ramlibacter decreased,and the relative abundance of pathogenic fungi such as Arthrinium and Gaeumannomyces increased.In conclusion,zinc application can affect the transformation of nitrogen and phosphorus in rice rhizosphere soil by changing the rhizosphere soil microbial community structure,soil enzyme activity and expression levels of key genes involved in nitrogen and phosphorus cycling.The application of zinc fertilizer with suitable nitrogen and phosphorus levels can promote the enrichment of denitrifying bacteria,phosphate-solubilizing bacteria and saprophytic fungi in the rhizosphere soil of rice,inhibit the activities of nitrosifying bacteria and pathogenic fungi,and increase the activities of protease,acid phosphatase and cellulase.The expression levels of genes such as Nap A and nrf A related to denitrification into ammonium,and pho C,pho D,ppk,pqqc related to phosphate solubilization were up-regulated significantly,thereby increasing the content of available phosphorus in the rhizosphere soil and promoting the conversion of nitrate nitrogen to ammonium nitrogen.Therefore,Zn application improved nitrogen and phosphorus availability,and promoted rice growth and nutrient uptake.