Effects Of Simulated Nitrogen Deposition On Soil Physicochemical Properties And Enzyme Activities Of Osmanthus Fragrans Plantations

The object of this experiment is Osmanthus fragrans forest,which has been growing for 7 years in Pingshan of Nanjing.Three nitrogen deposition levels were set up including CK(0g/(m2·a)),low level nitrogen treatment LN(8g/(m2·a)),and high level nitrogen treatment HN(15g/(m2·a)).A simulated nitrogen deposition experiment was conducted in a growing season to study,One-way analysis of variance and LSD method were used to analyze the characteristics of soil physicochemical properties and enzyme activity to study the effect of nitrogen deposition on soil properties of Osmanthus fragrans plantations,the purpose of this study is to understand the response mechanism of Osmanthus forest to nitrogen deposition,and provide a theoretical reference for the future cultivation and management of garden trees in the background of nitrogen deposition.The results as follows: 1 Effects of nitrogen deposition on the physical and chemical properties of soil1)Nitrogen deposition had little effect on the vertical distribution of soil bulk density,p H,water content,available nitrogen,total phosphorus and available phosphorus content,and only a small part of variance analysis was significant(P<0.05).Nitrogen deposition made the content of organic carbon and total nitrogen significantly decreased with the increase of soil depth,while the decreasing amplitude did not show a uniform rule with the increase of nitrogen application.2)Nitrogen deposition increased bulk density,p H,water content,total nitrogen and total phosphorus content of each soil layer,but most of which did not increase significantly.The soil bulk density decreased firstly and then increased with the increase of nitrogen application.The soil water content increased firstly and then decreased with the increase of nitrogen application.PH and total phosphorus did not show a uniform rule with the increase of nitrogen application.Nitrogen deposition increased organic carbon and available phosphorus content of each soil layer,most of which increased significantly,but it did not show a uniform rule with the increase of nitrogen application.Nitrogen deposition significantly increased the content of available nitrogen in each soil layer,showing HN>LN>CK.Nitrogen deposition significantly affected the content of available potassium in soil,most of which showed a significantly increase in its content,and with the extension of nitrogen application time,its content decreased with the increase of nitrogen application.3)Nitrogen deposition had little effect on monthly dynamics of soil bulk density,water content,organic carbon,total nitrogen and total phosphorus content.After HN treatment,the peak period of available nitrogen content in all soil layers was in November,while after other treatments those in September.HN processing changed its monthly dynamics to a certain extent,and it was shown that the peak period changed from September to November.The peak of available phosphorus content in soil was mostly September.Compared with CK,nitrogen deposition changed the monthly dynamics of available phosphorus content in the 0-10 cm layer to a certain extent,and its peak period changed from November to September.The peak period of available potassium content in soil was May,except for 10-30 cm layer,nitrogen deposition had a more complicated effect on the available potassium content in the 10-30 cm layer.2 Effects of nitrogen deposition on soil enzyme activity1)The four enzyme activities in each month showed a significant decrease with the increase of soil depth(P<0.05).The most activities of invertase,phosphatase and catalase were significant different between soil layers under nitrogen deposition(P<0.05),nitrogen deposition has little effect on the vertical change of urease activity.With the increase of nitrogen application rate,there was no uniform influence rule.2)In every month,nitrogen deposition significantly increased sucrase activity and urease activity in all soil layers(P<0.05),and the activity of urease under different treatments showed HN>LN>CK;Nitrogen deposition significantly increased phosphatase activity and catalase activity in 0-10 cm layer(P<0.05),and The activity of phosphatase under various treatments showed LN > HN > CK.3)On the whole,the monthly dynamics of the four enzyme activities in all soil layers were obvious after every treatment,and most of the peak values appeared in September.Compared with CK,nitrogen deposition changed the monthly dynamics of the 0-10 cm layer sucrase and catalase activity in each soil to a certain extent,showing that the peak period changed from July to September.