Responses Of Litterfall To Simulated Nitrogen Deposition In An Evergreen Broad-leaved Forest In Northern Subtropics

Litterfall is recognized as the critical pathways of organic matter and nutrient fluxes in forest ecosystems, and is an important part of ecological functions of ecosystem. This research was conducted to study on litterfall dynamics and its nutrients in a subtropical evergreen broad-leaved forest under simulation of nitrogen (N) deposition at Shitai during April 2011 to June 2013. The experiment was designed as follows:the control (CK), low N treatment (LN,50 kg N·hm2·a-1), high N treatment (HN,100 kg N·hm2·a-’)s high N+P treatment (HN+P 100 kg N·hm2·a-1+50 kg P·hm2·a-1). The purpose of the study is to determine the effects of simulated N deposition on forest litterfall and its chemical composition, and to provide the basis for restoration and sustainable management of subtropical evergreen broad-leaved forest. The results obtained from 1-year experiment are given in the following.1. Litterfall productionThe annual mean litter production for the experimental on Castanopsis eyrei stands was 7.78 t·hm·-2a-1 for CK,8.81 t·hm-2-a-1 for LN,9.08 t·hm-1·a-1 for HN and 9.41 t·hm-2·-a-1 for HN+P. The three treatments had a positive effect on litter production. The annual litter production of Castanopsis sclerophylla stands averaged 8.17 for CK,9.71 for HN and 9.02 t·hm-2 for HN+P, respectively. The HN and HN+P treatment increased the annual litter production. The annual litterfall productions in this study are within the range of subtropical forest zone reported.2. Litterfall componentsThe order of the litterfall components ranked consistently by their amounts as: foliage> branches> fruit> impurities. There existed significant differences among litterfall components and their proportion to the total litterfall for the sampling stands. Foliar litter was the primary composition in litterfall.3. Litterfall patternThe monthly litterfall in all treatments of Castanopsis eyrei stands and Castanopsis sclerophylla stands showed similar seasonal patterns, with two peaks occurred in April to May and in November. The seasonal patterns of litterfall were similar among the different treatments, suggesting that nitrogen deposition did not change the eco-physiological characteristics of the dominant trees.4. Nutrient in litterfallThe nutrient input by litterfall was in order of N> K> Ca> Mg> P. LN, HN and HN+P treatments elevated the average concentrations of N in the litterfall compared with CK. All of the nutrient elements in the foliar litter showed strong seasonal changes.In the Castanopsis eyrei stands, the annual N fluxes from litterfall to the forest floor for the different treatments were 50.96 kg·hm-2 for CK,65.56 kg·hm-2 for LN, 64.92 kg·hm-2 for HN and 71.29 kg·hm-2 for HN+P. The annual P fluxes were CK, 1.37; LN,1.59; HN,1.76 and HN+P,1.74 kg·hm-2; K fluxes:CK,37.98; LN,45.71; HN,43.77 and HN+P,40.69 kg-hm"2; Ca fluxes:CK,35.72; LN,45.84; HN,42.02 and HN+P,51.67 kg·hm-2; and Mg fluxes:CK,19.36; LN,26.70; HN,24.74 and HN+P,23.92 kg-hm"2. Three treatments increased the annual fluxes and was in order of HN+P> LN> HN> CK. In the Castanopsis sclerophylla stands, the annual N fluxes were, respectively, to the forest floor for the different treatments was estimated, at 58.22 kg·hm-2 for CK,77.83 kg·hm-2 for HN and 70.80 kg·hm-2 for HN+P; and P fluxes were 2.05 kg·hm-2 for CK,2.50 for HN, and 2.86 for HN+P; K fluxes 46.71 kg·hm-2 for CK,63.85 for HN, and 60.56 for HN+P; Ca fluxes 57.84 kg·hm-2 for CK, 71.40 for HN, and 63.10 for HN+P; Mg fluxes 17.31 kg·hm-2 for CK,19.52 for HN, and 19.33 for HN+P. The results indicated that the annual fluxes were increased by HN and HN+P treatments. However, the order was HN>HN+P>CK.5. C/N ratios in litter componentsAfter 2-year treatments, the N concentration in the foliar litter increased with increasing nitrogen deposition. Thus, the C/N ratios decreased obviously. The results from the study suggest that nitrogen deposition has a clear effect on litter production and its chemistry in this subtropical evergreen broad-leaved forest. In order to alleviate the adverse effect of high nitrogen deposition, other necessary elements especially P should be input.