Litter Decomposition And Its Responses To N Deposition For Coniferous Forests Of Qinling Western Mountains

On the basis of investigating and analyzing coniferous forest type,distribution and natural conditions in Gansu Xiaolong mountain area,the study was conducted in 6 fastgrowing coniferous forest of Pinus Tabulaeformis Carr,Pinus rigida Mill,Picea asperate Mast,Picea abies,Larixprincipis ruprechtii Mayr,Larix kaempferi Carr of Oinling Western Mountains,which site condition and forest factor are basically consistent and distribution areas are broader.Nitrogen addition experiment were initiated in the 2006 and composition processes were examined over an 24-month period by the litterbag,and 3 nitrogen addition treatments were established in the plots treatment(0kg/hm²Â·a),low nitrogen(57.8kg/hm²Â·a),high nitrogen(228 kg/hm²Â·a), ammonium nitrate(NH₄NO₃) solution was sprayed quarterly.Besides that,the mass loss of litter and the concentration,remaining rate,release patters of C,N,P,K were studied.The results showed that:(1) The initial chemical composition of the litter influenced decomposition rate,and significant negative correlation were found between the litter decomposition rate and N,C/N,N/P in the control experiment(P＜0.01).Compared with the control experiment,the correlation direction between decomposition rate and C,P,lignin/N,C/N,N/P were changed in the low nitrogen or high nitrogen experiment.Meanwhile, compared with the low experiment,the correlation of these are strengthened in the high nitrogen experiment and have reached significant level(P＜0.01).(2) The decomposition pattern was characterized by using a expolynominal regression equation(y=ae^-kt).The effects of nitrogen deposition on litter decomposition rate in the coniferous forest in Oinling Western Mountains suggested a inhibited trend as time passed,But the external nitrogen amount inhibitory action to litter decomposition is changed or altered with tree species.(3) The annual litte decomposition rate ranged from 30%-45%in the coniferous forest in Oinling Western Mountains of climate transition zone of China(from south temperate zone to north subtropical zone).(4) The concentration of C was decreased with undulatory way during decomposing of litter,But the concentration of the N,P,K were increased with undulatory way during decomposing of litter.Although these treads were not disrupted by the nitrogen addition treatment,C,N,P,K concentration varied significantly for different tree species and different nitrogen addition lever.(5) The release pattern of C accords with the mode of release→enrichment→release under different N treatment except for Pinus Tabulaeformis Carr litter.But the release pattern of N changed or responds to different tree species,and N release pattern accords with the mode of release→enrichment→release under treantment of N1 and N2.The condition of P is the same as C,namely the release pattern of P belongs to the mode of release→enrichment→release under different N treatment. While K release state takes on enrichment first and then released.(6) The positive correlation are found between C/element and residual rate of dry matters,and moreover,the correlation have reached significant level(P＜0.01) within most experiment scheme.At the same time,the significant positive correlation are not changed basically by external source nitrogen entering.Therefore,it shows that C/element can be regarded as a good index judging litters decomposition.