Effects Of Nitrogen Addition On Litter Yield And Nutrients Of Quercus Acutissima Forest In Urban And Rural Environmental Gradient

Since the industrial revolution in the 1970s,with the continuous development of the industrial and agricultural industries,the emissions of ammonia(NH3)and nitrogen oxides(NOx)have shown a significant increase.my country has become the world's third largest nitrogen deposition area after Europe and the United States.Atmospheric nitrogen deposition will cause a series of environmental and ecological problems.Therefore,domestic and foreign scholars have focused their attention on the research of atmospheric nitrogen deposition.Litter is an important part of the forest ecosystem as the link between organisms and soil for material circulation and energy flow.It plays an important role in maintaining forest water balance,community structure and soil fertility.This study selected Sawtooth oak forests in the central part of Anhui Province,including Sawtooth oak forests in Dashu Mountain(suburbs),Zipeng Mountain(outskirts)Sawtooth oak forests,and Wanfoshan(rural)Sawtooth oak forests in Shucheng County to carry out nitrogen addition experiments.The experiment was designed with 2 treatments and 1 control.The 2 treatments were:low nitrogen addition treatment(50 kg N·hm-2·a-1)and high nitrogen addition treatment(100 kg N·hm-2·a-1)).From August 2018 to June 2019,forest litter collection was carried out to analyze the response of litter amount and nutrient content of different gradients of Sawtooth oak forest to the addition of exogenous nitrogen.The main results are as follows:1)Litterfall characteristicsIn general,the litter yield accounts for the main part of the total litter.The dynamic change of the litter yield basically coincides with the trend and peak value of the total litter,which dominates the forest litter volume to a certain extent.The output of litter and fallen fruit is relatively small as a whole,and there is no obvious rule.The peak of litter and fruit yield mainly occurs in the fruit-fall period of tree species.The peak period of litter debris is mainly concentrated in August and December.2)Litter volumeStudies have shown that the total amount of litter in Sawtooth oak forests under different gradients has the largest yield under the addition of LN,with the largest in the outer suburbs,followed by the rural areas,and the smallest in the suburbs,respectively 11.80 t·hm-2·a-1 and 10.18 t·hm-2·a-1,10.04 t·hm-2·a-1.Nutrient addition failed to change the monthly dynamic pattern of litter.Under the different treatments of the three gradient oak forests,the annual litter yield was larger in the outer suburbs than in the rural areas than in the suburbs.In the outer suburban oak forest and the suburban oak oak forest,nitrogen addition has a promoting effect on the total amount of litter,while in the rural oak forest,low nitrogen promotes and high nitrogen inhibits.In general,nutrient addition failed to make the amount of litter break through the regional limit.3)Litter nutrientsUnder different nitrogen treatments,the nutrient content of litter in the suburban oak forest,the outer suburban oak forest,and the rural oak forest were C>N>Ca>K>Mg>P.The effect of nitrogen addition on the content of N and P elements All showed a promoting effect.And there is a correlation between the month and other elements except the C element.In general,the nutrient content in the suburbs is higher than that in the outer suburbs and rural areas after nutrient addition.