Responses Of Litterfall And Soil Nutrient To Simulated Nitrogen Deposition In Subtropical Evergreen Broad-leaved Forest

Since the industrial revolution,the atmospheric nitrogen deposition has been significantly increased and this has resulted in nitrogen enrichment phenomenon in a large number of waters.The terrestrial ecosystem is also facing a series of serious ecological problems such as nitrogen overload.Therefore,in recent years,the nitrogen deposition has become one of the hot research topics in the world.The research of atmospheric nitrogen deposition has received unprecedented attention.China is one of the biggest countries which has high atmospheric nitrogen deposition,however,its research on the atmospheric nitrogen deposition is relatively backward.This experiment was conducted in a matured evergreen broad-leaved forest in Xianyu Mountains in Shitai County of Anhui.Three treatments with a control?CK?were designed.The treatments were as low nitrogen?LN?,high nitrogen?HN?and high nitrogen plus phosphorus?HN+P?.We discussed the change of the litter production and soil chemistry caused by the simulated nitrogen deposition.The results are as follows.1.Litter productionThe simulated nitrogen deposition increased the litter production.HN+P(9.47 t·hm^-2·a^-1)>LN(8.86 t·hm^-2·a^-1)>HN(8.42 t·hm^-2·a^-1)>CK(7.90 t·hm^-2·a^-1).The result showed that the appropriate amount of nitrogen deposition can increase the litter production.However,there was no significant difference in litter production among the different treatments.The amounts of different litter components ranked as:foliage?49.33%?55.06%?>fruits?23.23%?26.99%?>branches?11.14%?13.28%?>miscellaneous?7.04%?9.39%?>flowers?1.30%?2.41%?>barks?0.28%?1.17%?.The foliar litter was the dominant component of litterfall.There were different responses of litter components to the different N treatments.The amount of foliar litter was significantly higher in LN(4.88 t·hm^-2·a^-1)than in CK(4.18 t·hm^-2·a^-1)?p=0.023?.The amounts of flower litter were 0.23t·hm^-2·a^-1 in HN+P and 0.10 t·hm^-2·a^-1 in CK,which was in marginal significance?p=0.054?.No significant difference was found for other litter components,which could be due to the different acquisition of nitrogen for different plant organs.The patterns of litter production mainly appeared as bimodal type.The first peak appeared in April and the second peak in November.The lowest litterfall occurred in March.The litterfall patterns were the same for the different N treatments.2.Litterfall nutrientsIn this study,the annual total fluxes by litterfall to the forest floor for the different treatments are as follows:HN+P(4.62 t·hm^-2·a^-1)>CK(4.44 t·hm^-2·a^-1)>HN(4.17 t·hm"2·a^-1)>LN(3.96 t·hm^-2·a^-1).No significant differences were found for different treatments.There existed significant difference in annual fluxes of N and P between HN+P and CK.The nutrient returns from foliar litter covered 52%-58%of the annual fluxes.3.Soil propertiesThe study showed that nitrogen treatment obviously decreased soil pH and increased the electrical conductivity and soil moisture.The amount of total nitrogen and available nitrogen in the soil can be improved.Meanwhile,nitrogen treatment increased soil organic carbon content.It ranked as CK(44.44 g·kg^-1)<LN(53.07 g·kg^-1)<HN(54.29 g·kg^-1)<HN+P(59.39 g·kg^-1).There did existed significant difference in soil organic carbon between CK and HN.There was also significant difference between CK and HN+P.4.Effects of root cutting on physical and chemical properties of surface soil?0-10 cm?The results showed that the root existence decreased soil pH,LN:D?4.37?>WD?4.29?;HN:D?4.35?>WD?4.14?;HN+P:D?4.13?>WD?4.06?.The root existence could increase the content of moisture,CK:WD?48%?>D?45%?;LN:WD?50%?>D?47%?;HN:WD?54%?>D?48%?;HN+P:WD?49%?>D?43%?;HN+P:WD?49%?>D?43%?.The EC of surface soil became higher after the treatment of root cutting.Thus forest root play an important role in regulation of soil nutrients.Root cutting had a significant effect on soil N.Different N treatments showed the similar results:CK,WD(2.6 g·kg^-1)>D(2.01 g·kg^-1);LN,WD(2.97 g·kg^-1)>D(1.94 g·kg^-1);HN,WD(3.0 g·kg^-1)>D(1.84 g·kg^-1);HN+P,WD(3.12 g·kg^-1)>D(1.92 g·kg^-1).The existence of root could help the accumulation of organic carbon in surfacesoil.The soil organic carbon was significantly lower in root cutting than root existence,the differences were as CK(10.46 g·kg^-1),LN(14.71 g·kg^-1),HN?22.48 g·kg'1?,and HN+P(23.11 g·kg^-1).