Simulated Nitrogen Deposition On Soil Carbon And Nitrogen Dynamics In A Subtropical Evergreen Broad-leaved Forest

In recent years,the study on atmospheric nitrogen deposition has brought to great attention in many countries.The function and effect of terrestrial ecosystems were seriously damaged as consistent increasing of N deposition.High N deposition had caused forest degradation.Therefore,N deposition has been drawn great attention.China is a country with high N deposition.However,the research on nitrogen deposition in China started late,with lack of monitoring network.This study was conducted in a subtropical evergreen broad-leaved forest at Zhawan Natural Reserve,southern Anhui.The objective of the study is to reveal the effects of simulated N deposition on soil carbon and nitrogen dynamics in subtropical evergreen broad-leaved forest.The results obtained are as follows.Nitrogen addition can improve soil N availability.The NH₄⁺-N content in the soil showed a decreasing trend from surface to deep layers.The annual average of NH₄⁺-N content in the soil on the slope stand show that: 0-10cm?20.96 mg kg-1?>10-20cm?12.55 mg kg-1?>20-30cm?10.80 mg kg-1?,and on the top of slope show that: 0-10cm?17.07 mg kg-1?>10-20cm?11.42 mg kg-1?>20-30cm?9.5 mg kg-1?.The NH₄⁺-N content was significantly higher in surface soil layer than in the deep layers.In addition,NH₄⁺-N content was higher in N+P treatment than in N treatment.NH₄⁺-N annual average content on the slope stand show N+P?20.34 mg kg-1?>N?19.2 mg kg-1?,on the top of slope N+P?20.08 mg kg-1?>N?14.46 mg kg-1?.Soil NO3--N content showed clearly seasonal variation with a high content in dry season and low in rainy season.The rate of soil ammonification was increased just after the N addition.The annual average rate of soil ammonification in 0-10 cm soil layer show CK?221.87 ?g kg-1 d-1?> N?117.80 ?g kg-1 d-1?> N+P?64.04 ?g kg-1 d-1?,in 10-20 cm soil layer show N?38.41 ?g kg-1d-1?>CK?27.04 ?g kg-1 d-1?> N+P?4.13 ?g kg-1 d-1?.The rate of soil ammonification was higher in N treatment than in N+P treatment.The nitrification rate was enhanced with the nitrogen accumulation in soil.The high nitrification rates appeared in high temperature season.The nitrification rates were higher in surface soil than in subsoil.On the slope stand,0-10cm?190.30 ?g kg-1 d-1?>10-20cm?38.88 ?g kg-1 d-1?,on the top of slope,0-10cm?284.59 ?g kg-1 d-1?>10-20cm?78.74 ?g kg-1 d-1?.The Different treatments had clear effects on soil DOC and DON,but were different in different forest.The DOC and DON content was higher in N treatment than in N+P treatment on the slope stand.The DOC content show N?759.38 mg kg-1?>N+P?646.99 mg kg-1?,DON content show N?96.30 mg kg-1?>N+P?95.22 mg kg-1?;However,the DOC and DON content showed different performance on the top slope stand,The DOC content showN+P?785.33 mg kg-1?>N?713.27 mg kg-1?,DON content show N+P?110.09 mg kg-1?>N?105.56 mg kg-1?.Soil MBC content showed a clear seasonal variation,which was significantly lower in autumn than in spring and summer.The MBC content showed as MBC?0-10 cm?> MBC?10-20 cm?> MBC?20-30 cm?.Slope stand in different treatment in the form of : CK?1235.64 mg kg-1?> N + P?1161.44 mg kg-1?> N?1090.21 mg kg-1?,the top slope stand in the form of : N + P >?1093.14 mg kg-1?>N?1003.98 mg kg-1?> CK?986.17 mg kg-1?.Fertilization treatment effect is obvious on the top slope stand,and N+P treatment perform better.The N treatments failed to increase the content of soil MBN.The average contents of MBN were lower for N and N+P treatments than for CK.on the slope stand: CK?68.47 mg kg-1?>N?58.62 mg kg-1?>N+P?57.49 mg kg-1?,on the top slope stand: CK?90.23 mg kg-1?>N+P?81.15 mg kg-1?>N?79.05 mg kg-1?.The distribution of MBN content along soil layers was consistent with the MBC,with an order of MBN?0-10 cm?> MBN?10-20cm?> MBN?20-30 cm?.