Effects Of Nitrogen Addition On Soil Respiration Rate And Soil Physicochemical Properties In The Urban Greenland

The increase of atmospheric nitrogen deposition changes the soil properties and affects the carbon and nitrogen cycle of terrestrial ecosystem.In order to clarify the effects of nitrogen deposition on urban greenland,soil respiration rates and soil physicochemical properties were measured in four nitrogen addition treatments from May to December in 2020.The greening trees of 7 years old sugar maple(Acer saccharum Marshall),red maple(Acer palmatum Thunbf.),tallow(Sapium sebiferum(L.)Roxb.),sumachs(Cotinus coggygria Scop.),and crimson leaved maple(Acer ginnala Maxim.)which growing in the teaching and practice base of agricultural garden in Anhui Agricultural University were selected.With urea(CH₄N₂O)as the nitrogen source,four nitrogen treatments wrere set as control(CK,0 g·m^-2·a^-1),low nitrogen(N1,5g·m^-2·a^-1),medium nitrogen(N2,10g·m^-2·a^-1),and high nitrogen(N3,15 g·m^-2·a^-1).The soil respiration rates of five greenland were measured by LI-8100 Soil Flux System.One-way ANOVA and Pearson correlation coefficient were used to analyze the dynamic changes of soil respiration rate,soil physicochemical properties and soil enzyme activities,and their response to nitrogen addition.The main results showed as follows:(1)The diurnal and monthly variations of soil respiration rates of the five greenlands in different nitrogen treatments were unimodal.The maximum daily soil respiration rates occurred from 12:00 to 14:00,and the soil respiration rates in August and September were significantly higher than that in other months.(2)Nitrogen addition promoted the soil respiration rates of the five greenlands.The order of the increasing of soil total respiration rates in different nitrogen treatments was N2>N1>N3.The order of root respiration rates increasing in different nitrogen treatments in tallow greenland was N1>N2>N3,and other four greenlands all were N2>N1>N3.(3)The soil total respiration rate and root respiration ratere of five greenlands were different in different nitrogen treatment levels.The order of soil total respiration rates in N1 treatmnts was sumachs>sugar maple>red maple>tallow>crimson leaved maple,sugar maple>tallow>red maple>sumachs>crimson leaved maple in N2,and sumachs>red maple>sugar maple>tallow>crimson leaved maple in N3.The order of root respiration rates in N1 treatmnts was sumachs>red maple>sugar maple>tallow>crimson leaved maple,tallow>red maple>s umachs>sugar maple>crimson leaved maple in N2,and red maple>sumachs>tallow>sugar maple>crimson leaved maple.(4)Nitrogen addition decreased the soil pH value.But there was no significant difference among four nitrogen treatments.The increasing of contents of soil organic carbon,total nitrogen,and total phosphorus in N1 and N2 treatment were higher than those in N3 treatment(P<0.05).The increase of soil microbial biomass carbon and soil microbial biomass nitrogen was not significant among N1,N2,and N3 treatment.(5)Under different nitrogen concentrations,the changes of soil enzyme activities of the five greenland in four nitrogen treatment were unimodal from May to December.The soil urease activities in N1 and N2 treatment were higher than that in N3 treatment,significantly(P<0.05).The soil neutral phosphatase activities in N1 treatment increased significantly(P<0.05),and not significant in N2 and N3 treatments.The soil catalase activities increasing were not significant with nitrogen addition.In conclusion,the changes of soil respiration rate were induced by the combined effects of soil temperature,soil humidity,soil physi-chemical properties,and soil enzyme activities.N3 nitrogen addition treatment reduced soil nutrients and soil enzyme activities,which slowed down the soil respiration rate in the urban greenlands.