Effect Of Soil Cd Pollution On Nitrification Activity Of The Rhizosphere Soil Of Robinia Pseudoacacia L.seedlings

Soil nitrification is a very important biological process in the soil nitrogen cycle,it is highly sensitive to environmental conditions such as heavy metal pollution.In recent years,with the rapid development of industry and agriculture in China,soil heavy metal pollution,such as Cd pollution,has become more and more serious,and various environmental and ecological problems brought about by this have become increasingly prominent.Much progress has been made in the study of the effects of heavy metal pollution on soil nitrification,however,the response of soil nitrification activity to different heavy metals may not be consistent,and previous studies rarely involve soil nitrification activity of rhizosphere.Since the rhizosphere is the most active area for material exchange between plants and soil,which is related to plant growth and production,therefore,it is important and necessary to explore the influence of heavy metal pollution on the nitrification activity of rhizosphere soil.Therefore,this experiment took Robinia pseudoacacia L.seedlings as the research object and used the pot experiment method to explore the influence of Cd pollution on the nitrification activity of rhizosphere soil of Robinia pseudoacacia L.seedlings.The main research results and conclusions are as follows:1.Cd pollution has different effects on rhizospheric soil characteristics of Robinia pseudoacacia L.seedlings.The total C and p H of rhizosphere soil of Robinia pseudoacacia L.seedlings increased significantly under Cd pollution,The maximum values are 13.53 mg g^-1and 8.19,respectively.But Cd contamination had no significant effect on soluble C,total N,soluble N,C/N and soluble C/N.The content of Cd in rhizosphere soil decreased with the growth time of Robinia pseudoacacia L.seedlings.2.Different soil nitrifying enzymes have different sensitivity to Cd contamination.Cd contamination significantly inhibited HAO activity in rhizosphere soil,but had no significant effect on AMO and NXR activities.The total C,total N and p H of rhizosphere soil were negatively correlated with HAO activity.At 90 days of seedlings growth,the rhizosphere soil C/N was significantly positively correlated with HAO activity,the soluble C was significantly negatively correlated with AMO activity,and the content of rhizospheric Cd was significantly negatively correlated with NXR activity.3.Soil Cd pollution has a significant impact on the genetic diversity of AOA,AOB and NOB.Cd content in rhizosphere soil was negatively correlated with AOB gene diversity,but not significantly correlated with AOA and NOB,and did not change the dominant flora of AOA,AOB and NOB.The total C,C/N and p H of the rhizosphere were significantly correlated with the genetic diversity of AOA,and p H significantly affected the genetic diversity of NOB,while soluble N and soluble C/N significantly affected the genetic diversity of AOB.4.Soil Cd pollution has a significant impact on the gene abundance of arch-amo A,amo A and nxr A.The overall expression of gene copy number of nitrifying bacterias in rhizosphere soil was:AOA>AOB>NOB,and Cd treatment increased the abundance of arch-amo A gene compared with the control group(Cd1).The p H of the rhizosphere was significantly correlated with the abundance of arch-amo A,amo A and nxr A genes.In addition,the total C and C/N of the rhizosphere also significantly affected the abundance of arch-amo A and amo A genes,and soluble N and soluble C/N significantly affected the abundance of nxr A gene.5.On the whole,Cd pollution has a certain degree of inhibition on the nitrification activity of rhizosphere soil.