Greenhouse Gases Emission And Microbial Communities In Remediation Process Of Degraded Vegetable Soils

Excessive application of nitrogen fertilizers in facilitated vegetable fields may easily lead to soil degradation(such as soil salinization,acidification,hardening,etc.),and even further to some serious environmental consequences like pollution of groundwater and emission of large volumes of N2O,thus seriously affecting sustainable development of the vegetable industry.Recently,a novel soil remediation technology,called RSD(reductive soil disinfestation)has been developed of adding organic substances(e.g.,crop straw,molasses,manure,etc.)in flooding water.The RSD method can effectively alleviate the risk of soil degradation,such as removing the nitrate accumulated in the soil,increasing pH,lowering soil electrical conductivity and improving soil structure.Thus,it is essential to investigate the environmental effect of RSD application in remediation process.Therefore,degraded facilitated vegetable soils were chosen as the materials.Two RSD methods was employed in this study,S+F RSD method(Rice straw + flooding)and S+WHC+M RSD method(Rice straw + Water Holding Capacity + mulch).Our aims were(i)to compare the remediation effect of these two RSD methods;(ii)to compare the emission regularity of greenhouse gases from degraded facilitated vegetable soils applied by these two RSD methods;(iii)to investigate the effect of biochar on the emission of greenhouse gases from degraded facilitated vegetable soils applied by these two RSD methods;(iv)to analysis the effect of RSD methods on soil bacterial and fungal communities.The main research results are as follows:(1)Results show that the application of S+F RSD method and S+WHC+M RSD method can effectively alleviate the risk of soil degradation,and no significant difference was observed in the improvement of soil physicochemical properties and the disinfection of soil-borne pathogens between two RSD methods.The emission regularity of N2O and CH4 from degraded facilitated vegetable soils applied by these two RSD methods was different.In strong reducing remediation process of degraded facilitated vegetable soils,N2O emission might be related to the Nitric oxide reductase activity of nitrifying microorganisms,and CH4 emission might be related to methanogenic activity.(2)The application of RSD methods in degraded facilitated vegetable soil(i)significantly reduced the abundance of soil bacterial 16S rRNA and fungal 18S rRNA genes;(ii)obviously increased the community richness of soil bacteria and decreased the community evenness;(iii)decreased the community richness of soil fungi and apparently increased the community evenness;(iv)altered the composition and structure of soil bacterial community.The relative abundances of Macellibacterides and Bacteroides(belongs to Bacteroidetes),Bacillus and Clostridium(belongs to Firmicutes),and MethanosarcineI(belongs to Euryarchaeota)were significantly increased after RSD application,while the relative abundances of Nitrosomonadaceae(belongs to Proteobacteria),Nocardioides and Arthrobacter(belongs to Actinobacteria)were significantly decreased after RSD application;(vi)compared to S+F RSD method,the application of S+WHC+M RSD method was more suppressive to the abundance of soil fungal 18S rRNA gene,and no significant difference was detected in diversity and structure of soil and fungal communities between S+F RSD method and S+WHC+M RSD.(3)The application of 5%biochar in degraded vegetable soil and its RSD process can elevate soil pH and alter abundances of the critical denitrifying functional genes,thus efficiently mitigating N2O emission.The abundance of norB and nosZ genes was also significantly changed after biochar application.Linear regression analysis shows that soil N2O emission was mainly related to nosZ gene abundance in degraded vegetable soil,but to norB gene abundance in RSD process.All the findings in this study can be regarded as important indices for assessment of environmental effects of the remediation of degraded vegetable soil.