Litterfall Production And Effects Of Stand Structure And Nitrogen Deposition In A Subtropical Evergreen Broad-leaved Forest

Litterfall,one of the most important aspects of the biogeochemical cycle,is a tie which can link plants and soil.Today,the greenhouse effect and acid subsidence is increasingly serious,it make the study of litterfall a more important practical meaning.In order to explore the relationship between litterfall production with stand structure and the effect of nitrogen deposition.An investigation of litterfall production in a subtropical evergreen broad-leaved forest was carried out from June 2014 to May 2015 at Zhawan Natural Reserve in Qimen,Anhui Province.This research was divided into 2 parts.One is to study Litterfall production and its relation to stand structural factors in a subtropical evergreen broad-leaved forest and another is to study litterfall production and its nutrients in a subtropical evergreen broad-leaved forest under simulation of nitrogen(N)deposition.The experiment was designed as follows: the control(CK),high N treatment(T1,100 kg N·hm-2·a-1),high N + P treatment(T2,100 kg N·hm-2·a-1+50 kg P·hm-2·a-1).The results was showed follow:1.Stand structure factorsThere are 26 species of trees in study area,belonging to 14 families,22 genera.Advantage tree are all Fagaceae with its dominance > 58%.Diameter class was different between forests and the mid-slope showed the unimodal type,however the flat ridge was reverse "J" shape.Species richness indices,uniformity indices and diversity indices are from 13 to 19,1.97 to 3.23,0.40 to 0.77 for the different sampling plots,respectively.All showed that the mid-slope less than the flat ridge.2.Litterfall production and componentsThe annual rate of litterfall ranged from 5.95 to 9.70 t·hm-2·a-1.There was no significant difference between the two stands(P > 0.05),except for fruit litter(P < 0.05).The annual total litterfall was ranked as P3 > P6 > P2 > P4 > P1 > P5,for the litter components,it was as foliage(66.21%)> fruit(14.54%)> miscellaneous(11.02%)>branch(7.91%)> bark(3.32%)> flower(1.35%).3.Relationship between litter production and forest factorsThe correlation analysis showed that total litterfall and foliar litter were significantly positively correlated(P < 0.05)with total basal area;foliar litter was significantly positively correlated with mean diameter at breast height(DBH)(P < 0.01).Fruit litter was significantly positively correlated with mean DBH and basal area of dominant-species(P <0.05)while was significantly negatively correlated with diversity index,evenness index and stand density(all P < 0.01).However,there was no significant correlation(P > 0.05)between woody litter and structural parameters.4.Litterfall rhythmThe annual variations of both foliar and total litterfall were bimodal type in P1 and P2 plots,while were irregular shape in plot P3 on the mid-slope and unimodal type in plot P4,P5 and P6 on the flat ridge.Twig had a peak in December and flower in May.5.Litterfall nutrient contents and nutrient returnThe nutrient concentrations in the different litter components was ranked as C > N >Ca > K > Mg > P.The concentrations of N and Ca in foliar litter had significant difference(P < 0.05)and P had extremely significant difference(P < 0.01)between the two stands.The annual nutrient returns ranged from 2.7 ~ 4.7 t hm-2 for C,75.75 ~ 105.58 kg hm-2 for N,2.07 ~ 3.67 kg hm-2for P,16.54 ~ 41.80 kg hm-2for K,74.61 ~ 109.91 kg hm-2for Ca,and 17.95 ~ 29.48 kg hm-2 for Mg.The nutrient returns by foliage,fruit and miscellaneous materials accounted for 71.17% ~ 95.75% for the different elements.There are some differences between the two forests.6.Litterfall stoichiometric ratioLitterfall C:N,C:P and N:P ratios on the mid-slope were 43,2041,and 47,respectively,while were 36,1264,and 35 on the flat ridge respectively.Foliage C:N ratio had a peak in December and C:P,N:P ratios on the mid-slope peaked in November.7.Response of litterfall to Nitrogen depositionThe treatments of T1 and T2 increased the total amount,and foliar litter production on the mid-slope,while the response was reverse on the flat ridge,but T2 increased foliar litter production.T1 and T2 treatments did not significantly change C and N contents in foliar litter.T1 significantly increased foliar K contents,reduced the K contents in fruits and Ca contents in miscellaneous(P < 0.05).T2 significantly reduced the K contents in fruits on the mid-slope(P < 0.05).T1 significantly increased K contents in the flowers,Ca contents in twigs and miscellaneous,Mg contents in twigs(P < 0.05).T2 significantly increased P,Ca,Mg contents in twigs(P < 0.05).