Effects Of Simulated Nitrogen Deposition On Surface Soil Nutrient In Natural Evergreen Broad-Leaved Forest In Rainy Area Of Western China

With the acceleration of the industrialization process,a large amount of fossil fuel combustion and industrial exhaust emissions,the rapid increase in atmospheric nitrogen,and nitrogen deposition increased,gradually changing the terrestrial ecosystem structure integrity and functional stability,Social sustainable development faced a serious threat.Forests play an important regulatory role in global climate change.Forest soil fertility will directly affect the productivity of forest ecosystems and indirectly affect soil geochemical cycles.The globalization of nitrogen deposition and the increasing trend will have a significant impact on soil fertility and indirectly alter global carbon and nitrogen balance.So,the surface soil?0?20 cm?of natural evergreen broad-leaved forest in rainy area of Southwest China was used as the research object.The soil pH and nutrient in the surface soil were studied from March 2014 to November 2015 by in situ simulated nitrogen deposition.Four levels of N treatments:control(CK,OkgN·hm²a^-1),low-N(LN,50 kgN·hm²a^-1),medium-N(MN,150 kgN·hm²a^-1)and high-N(HN,300 kgN·hm²a^-1)were set in the present study.The main results are as follows:?1?Soil pH value of natural evergreen broad-leaved forest in rainy area of Southwest China is between 6.35 and 6.53,and the soil is acidic.Nitrogen deposition reduced the soil pH in evergreen broad-leaved forest,and increased soil acidification,and the pH value was inversely proportional to the level of nitrogen application.The overall performance was CK>LN>MN>HN.?2?Nitrogen deposition has a greater effect on soil organic carbon.The results showed that MN and HN treatment increased the soil organic carbon,the average increase was 4.30%and 8.08%,LN treatment was not significant.?3?Nitrogen deposition significantly increased soil total nitrogen,nitrate nitrogen and ammonium nitrogen in evergreen broad-leaved forest,and significantly reduced soil available N.Compared with CK,LN,MN and HN treatments increased soil total nitrogen by 4.73%,5.53%and 10.23%,respectively.Soil NO3-N increased by 28.51%,50.13%and 86.28%,respectively.13.16%,27.85%and 49.75%,respectively.The soil available N decreased by 60.96%,61.76%and 63.12%respectively.?4?Soil inorganic nitrogen was mainly nitrate nitrogen in natural evergreen broad-leaved forest in rainy area of Southwest China,and nitrate nitrogen accounted for 57.90%of total inorganic nitrogen.The nitrogen concentration increased the proportion of nitrate nitrogen in inorganic nitrogen,and the treatments of LN,MN and HN were 60.96%,61.76%and 63.12%respectively.?5?Nitrogen deposition had little effect on soil total potassium.LN and MN treatments significantly increased the available K in soils,with an average increase of 2.83%and 4.66%,respectively.The HN treatment significantly reduced the available K in the soil,with an average decrease of 6.88%.?6?Nitrogen deposition had little effect on soil total phosphorus content,but significantly increased soil available phosphorus.Compared with CK,LN,MN and HN treatments increased soil available phosphorus by 104.69%,46.51%and 50.97%,respectively.?7?The soil nutrient index of natural evergreen broad-leaved forest in rainy area of Southwest China is different.The contents of soil organic carbon,total nitrogen,alkali nitrogen,ammonium and total potassium were higher in summer,while soil pH and nitrate showed higher winter,Soil available potassium,available phosphorus and total phosphorus had no obvious seasonal characteristics.In addition to soil pH,nitrogen deposition did not change the seasonal dynamics of soil nutrients.?8?The soil C/N,C/P and N/P varied from 13.78?17.16,38.95?49.18 and 2.27?4.15,respectively,in the evergreen broad-leaved forest in rainy area of Southwest China.Nitrogen deposition significantly reduced soil C/N,and significantly increasing soil C/P and N/P.The N/P value increased with the increase of nitrogen levels.In the context of a sustained increase in nitrogen deposition,phosphorus is becoming a limiting factor for the forest ecosystem.