Simulating Changes Of Leaching Characteristics And Bacterial Diversity Of Loam Under Different Rainfall Conditions

The leaching caused by rainfall is an important way to lose soil nutrients,leading to eutrophication of water bodies and agricultural non-point source pollution,which needs to be correctly understood by people.In this paper,some loam samples were selected and the annual rainfall conditions of 300,600,900 and 1200 mm were designed using indoor simulated soil columns.By comparing the concentration of nitrogen,phosphorus in the leaching solution and the cumulative leaching loss,the dissolution characteristics and leaching risk of these elements under different conditions were analyzed.And the effects of leaching on soil environmental changes were evaluated from the perspectives of soil bacterial population diversity and soil enzyme activities.Finally,as a new type of pollutant,Antibiotic Resistance Genes（ARGs）have great harm to the ecological environment.The soil column leaching experiment is used to study the changes of the ARGs content in soil under different water content conditions.At the same time,it can provide a scientific basis for formulating reasonable countermeasures to prevent soil ARGs pollution.The main conclusions are as follows:（1）There is a significant correlation between leaching and the loss of nitrogen and phosphorus（P<0.01）.The nitrate nitrogen（NO₃^--N）in the soil easily dissolves with the pore water,which is the main form of soil nitrogen leaching.When the amount of leaching water is small,it has a great influence on the dissolution of NO₃^--N and total nitrogen（TN）in the soil.The effect of increasing the amount of leaching water on NO₃^--N and TN is gradually reduced,but the risk of leaching of ammonia nitrogen（NH₄⁺-N）and total phosphorus（TP）is gradually increased.For the loam in this experiment,the NH₄⁺-N and TP were leached logarithmically in the leaching process,the leaching of NO₃^--N showed a linear growth,and the TN fits the quadratic equation most.（2）The leaching process leads to changes in soil moisture content and matrix suction,affecting bacterial movement in the soil.High-throughput sequencing results showed that Proteobacteria was the dominant bacteria in the soil samples of this experiment.The number of Proteobacteria in the soil column under different treatments accounted for more than 35%of the total.The increase of leaching water has improved the soil water environment,and the range of bacterial movement has expanded,which intensifies the cooperation and competition between microorganisms.Eventually lead to a reduction in soil bacterial diversity.The main dominant bacteria are less affected in the soil,and there is little change between bacterial communities.However,the proportion of the relatively low bacterial population will be reduced or even disappeared.（3）Changes in soil pore structure,water content and oxygen content caused by leaching significantly affected soil urease,acid phosphatase and invertase activities.With the increase of leaching water in the experiment,soil nutrient loss and environmental changes led to significant reduction of urease,acid phosphatase and invertase activities in each group of soil columns（P<0.05）,but the activity of catalase has not changed,basically.In addition,soil enzymes of the same functional type exhibit similar characteristics to external conditions.（4）The antibiotic resistance gene（ARGs）itself has biological properties that cause it to spread further during leaching.Leaching improves the soil water environment and promotes microbial growth,which indirectly leads to the spread and spread of ARGs.The content of ARGs in each treated soil column increased to varying degrees compared to the blank group.However,when the amount of leaching water exceeds a certain range,the time for the soil to be saturated increases,and the ARGs diffuses with the pore water to the deep layer,which in one aspect reduces the content of the ARGs in the original soil.