Responses Of Litterfall To Simulated Nitrogen Deposition In An Evergreen Broad-leaved Forestry In Qimen, Anhui

Litterfall is recognized as the critical pathways of organic matter and nutrient fluxesin forest ecosystems, and is an important part of ecological functions of ecosystem. Thisresearch was conducted on the dynamics of litterfall and its nutrients in a subtropicalevergreen broad-leaved forest under simulation of nitrogen （N） deposition at ZhawanNature Reserve in Qimen during July2011to July2012. The experiment was designedas follows: as the control （CK）, high N treatment (T1,100kg N·hm2·a^-1), high N+Ptreatment (T2,100kg N·hm2·a^-1＋50kg P·hm2·a^-1). The purpose of the study is todetermine the effects of simulated N deposition on forest litterfall and its chemicalcomposition, and to provide the basis for restoration and sustainable management ofsubtropical evergreen broad-leaved forest. The results obtained from1-year experimentare given in the following.1. Litterfall productionThe annual mean litter production for the experimental stands on the middle slopewas6.87t·hm^-2for CK,5.48t·hm^-2for T1and6.72t·hm^-2for T2. This indicated thathigh N deposition had a negative effect on litter production. On the flat ridge, however,the annual litter production averaged6.80,5.66and7.01t·hm^-2for CK, T1and T2,respectively. With comparison to CK, T2treatment increased while T1treatmentdecreased the annual litter production. The annual litterfall amounts are within the rangeof subtropical forest zone reported.2. Litterfall componentsThe order of the litterfall components ranked consistently by their amounts as:foliage＞branches＞sexual organs＞miscellaneous. There existed significantdifferences among litterfall components and their proportion to the total litterfall for thesampling stands. Foliar litter was the primary composition in litterfall.3. Litterfall patternOn the flat ridge, the temporal pattern of total litterfall showed two peaks, of whichone was from April to May and another from November to December. However,temporal pattern of total litterfall was irregular for the stands on the mid-slope. Theseasonal patterns of litterfall were similar among the different treatments, suggestingthat nitrogen deposition did not change the eco-physiological characteristics of the dominant trees.4. Nutrient of litterfallThe nutrient input by litterfall was in order of N＞K＞Ca＞Mg＞P. T1and T2treatments elevated the average concentrations of N by ranging from7.81%to22.33%in the litterfall compared with CK. T1treatment reduced the average concentrations of P,K and Mg. However, T2treatment increased the concentrations of P and Mg butdecreased K concentration. All of the nutrient elements in the foliar litter showed strongseasonal changes.On the mid-slope, the annual N fluxes from litterfall to the forest floor for thedifferent treatments were56.50kg·hm^-2for CK,49.49kg·hm^-2for T1and61.29kg·hm^-2for T2. The annual P fluxes were CK,1.71; T1,1.23; and T2,2.05kg·hm^-2; andK fluxes: CK,47.43; T1,36.29and T2,44.52kg·hm^-2; Ca fluxes: CK,34.18; T1,28.84and T2,36.30kg·hm^-2; Mg fluxes: CK,10.27; T1,8.93and T2,10.62kg·hm^-2. On theflat ridge, the annual N fluxes were, respectively, to the forest floor under the threetreatments （CK, T1, T2） was estimated, at48.10kg·hm^-2for CK,50.09kg·hm^-2for T1and62.79kg·hm^-2for T2; and P fluxes were1.51kg·hm^-2for CK,1.29for T1, and2.30for T2; K fluxes45.27kg·hm^-2for CK,36.33for T1, and46.48for T2; Ca fluxes37.71kg·hm^-2for CK,31.57for T1, and38.71for T2; Mg fluxes10.21kg·hm^-2for CK,8.67for T1, and10.74for T2. The results indicated that the annual N flux was increasedwhile the other nutrient （P, K, Ca and Mg） fluxes were decreased by T1treatment.However, the T2treatment increased the annual fluxes of N, P, Ca and Mg whiledecreased the annual K flux.5. C/N ratios in litter componentsAfter1-year treatments, the N concentration in the foliar litter increased withincreasing nitrogen deposition. Thus, the C/N ratios decreased obviously.The results from the study suggest that nitrogen deposition has clear effect on litterproduction and its chemistry in this subtropical evergreen broad-leaved forest. In orderto alleviate the adverse effect of high nitrogen deposition, other necessary elementsshould be input.