Effects Of Drought Stress At Maize Seedling Stage And Nitrogen Application On Soil Properties And Microbial Communities

In order to clarify the changes of rhizosphere and bulk soil properties and microbial communities to drought stress at seedling stage and nitrogen application,and the response mechanism of soil properties and microbial communities to nitrogen application after drought stress at seedling stage and restoration of natural rainfall conditions.In this study,pot experiment and field experiment were carried out to study soil microbial biomass carbon and nitrogen,soil enzyme activities and soil bacterial and fungal community structure in rhizosphere and bulk soil of maize at seedling stage under different soil moisture and nitrogen application rate,and explore the response characteristics of different soil moisture and nitrogen application rate to the community structure of soil properties,bacteria and fungi in different periods under the condition of natural rainfall restoration after drought stress at the seedling stage.It is expected to be the theoretical basis for the research on the regulation mechanism of soil microorganisms in the farmland soil system.The main findings are as follows:1.The results of pot experiment showed that different soil moisture and nitrogen application rates have significant effects on the biochemical properties of rhizosphere and bulk soil.Nitrogen application increased rhizosphere and bulk soil ammonium nitrogen,nitrate nitrogen,microbial biomass carbon and nitrogen content,and there was a significant correlation between soil ammonium nitrogen,nitrate nitrogen and urease activity.The response of microbial biomass carbon and nitrogen to water changes is significantly different in rhizosphere and bulk soil.Rhizosphere soil microbial biomass carbon and nitrogen are lower under suitable water conditions,while bulk soil microbial biomass carbon and nitrogen are lower under drought conditions.Soil moisture and nitrogen application has significant effects on rhizosphere soil nitrate reductase,nitrite reductase and bulk soil nitrite reductase,and two factors affect rhizosphere soil nitrite reductase and bulk soil urease and nitrite reduction and FDA hydrolase activities show significant interaction.2.Alpha diversity analysis showed that soil moisture and nitrogen application had no significant effect on the richness and diversity of rhizosphere soil bacterial communities.Nitrogen application significantly reduced the abundance and diversity of bulk soil bacterial communities under different water conditions.Analysis of the composition of the species population showed that Actinobacteria,Proteobacteria,and Acidobacteria are the main dominant phyla of rhizosphere and bulk soil bacteria,accounting for 57.1%-88.5%.The results of principal component analysis showed that the bacterial community structure of rhizosphere and bulk soil was significantly affected by nitrogen application.Redundant analysis results show that microbial biomass carbon,nitrogen and p H are the main factors affecting the bacterial community structure in rhizosphere and bulk soil.Nitrogen application under different water conditions significantly increased the richness index of rhizosphere soil fungi and decreased the diversity index of fungi.The dominant groups in rhizosphere and bulk soil are similar,and the dominant phyla with the highest relative abundance is Basidiomycota.Nitrogen application under different water conditions reduced the relative abundance of Basidiomycota and increased the relative abundance of Ascomycota.The results of principal component analysis showed that nitrogen significantly affected the fungal community structure of rhizosphere soil,but there was no significant difference in fungal community structure of bulk soil between different treatments.3.The results of field experiment showed that different soil moisture and nitrogen application rates significantly changed the soil physical and chemical properties under the conditions of different periods.Nitrogen application before water control significantly increased soil p H,ammonium nitrogen and nitrate nitrogen content.After water control,soil ammonium nitrogen and nitrate nitrogen are significantly affected by soil moisture,which was significantly higher than that under drought stress conditions.There was no significant difference in soil p H between the treatments in the maturity period.Soil ammonium nitrogen and nitrate nitrogen were only significantly affected by nitrogen application,and soil moisture,the interaction of soil moisture and nitrogen had no significant effect on them.4.Short-term drought stress reduces the abundance and diversity of soil bacteria.After the restoration of natural precipitation,the bacterial diversity of water suitable treatment increases.The analysis of the composition of the species showed that the number of soil bacteria OTU/ASV treated with MW75N0 and MW75N1 increased significantly.A total of 33 bacterial phyla were detected in the soil,of which the dominant phyla were Proteobacteria,Actinobacteria,Acidobacteria.The abundance of soil fungi was not affected by short-term drought stress,and the abundance and diversity of soil fungi increased significantly after the restoration of natural precipitation.The phyla with relative abundance greater than 1% in all treatments were Ascomycota,Basidiomycota,Mortierellomycota.Drought stress caused the relative abundance of Ascomycota to increase,and the relative abundance of Basidiomycota to decrease.The principal coordinate analysis shows that after a short-term drought stress and a later recovery of natural precipitation,there are significant differences in soil microbial communities structure in different periods.Among them,the bacterial and fungal communities that are suitable for water treatment in the mature period are significantly different from other treatments.