| Carbon and Nitrogen cycles of forest ecosystem are the most important material cycle of forest ecosystem processes,which exists in the Soil-Plant-Atmosphere-Continuum(SPAC)and linked tightly through a series of physiological and ecological functions.The changes in the SPAC have strong impact on the material cycle in the whole forest ecosystem inevitably.With the development of the urbanization and industrialization,the increases of the greenhouse gases concentrations and nitrogen deposition,caused enormous changes in the C and N cycles of forest ecosystem.However,most present studies focused on a single C cycle or N cycling in forest ecosystems,and the study on the feedback mechanism and C and N cycle coupling of forest ecosystem was little,especially in the background of global change the coupling relationship was become a key issue that needs urgent solutions.This study selected larch(Larix gmelinii)in cold temperate zone and investigate the distributional patterns of carbon and nitrogen,photosynthesis,litter decomposition,soil microbial biomass carbon and nitrogen with the method of experimental ecology.Based on the field measurements,the parameters in the Forest-DNDC model were calibrated and analysis the carbon and nitrogen cycling characteristics in four climate change scenarios.The results may help for the larch forest ecosystem management and decision-making.The results showed that:1.Carbon/Nitrogen storage per unit for the larch forest ecosystem in cold temperate zone was 169.29～435.57 t·hm-2 and 294.71～1255.27 kg·hm-2 respectively,with a considerable difference in different ecosystems.Soil carbon storage occupied 69.9%～93.1%of the total carbon storage in the larch forest ecosystem.Nitrogen storage in larch forest ecosystem had a close relationship with forest type.Nitrogen in true moss-larch ecosystem(56%)and Rhododendron dauricum-larch ecosystem(77%)mainly distributed in soil,while herbage-larch ecosystem(79%)and Ledum-larch ecosystem(68%)mainly distributed in the plants.2.The strong relationship between net photosynthesis rate(Psn)and sunlight intensity,temperature,stomatal conductance and atmosphere humidity.The Psn value for larch increased with the concentration of CO2.The concentration of atmospheric CO2 doubled caused Psn value increased by 0.90 times for larch canopy.The relationship between Psn value and Potassium concentration in leaf was significant(R2=0.8228),but not significant was found in Psn value and nitrogen concentration.The deficit of Potassium availability in larch forest in cold temperate zone may weaken the influence of nitrogen deposition on potential of photosynthetic carbon sequestration.3.Nitrogen deposition profoundly affected litter decomposition and nutrient release of larch forest ecosystem.Nitrogen deposition reduced the ratio of C/N from average of 4.78%-11.38%and had significant influences on the nutrient release of P,K,Ca and Mg.Nitrogen deposition was significantly enhanced nitrogen storage in litter composition.Low level nitrogen input increased the release of carbon in the litter,while high level nitrogen input decreased the release.4.A remarkable linear relationship between soil total nitrogen(TN)and soil organic carbon(SOC)was found in larch forest in cold temperate zone(p<0.01).The short term input of nitrogen significantly affected soil carbon pools.As a whole,nitrogen deposition enhanced concentrations of DOC,Macro-POC and Micro-POC in soils and reduced the δ13CMacro-POM,δ13CMicro-POM and δ13CMOM values in surface soils.Different types and different levels of N deposition exhibited obvious difference on larch forest soil carbon pools.Medium and low level nitrogen deposition promoted the increase of soil carbon pools,while high level nitrogen deposition can decrease of soil carbon pools.Short term nitrogen deposition was not significant affected on soil carbon flux for larch forest and soil temperature was the most important key parameters to influence the soil respiration.5.The dynamic characteristics of surface soil microbial carbon/nitrogen were consistent with the change of soil microbial biomass.The maximum of soil microbial carbon/nitrogen were 564±60 mg·kg-1 and 70.09±4.61 mg·kg-1,respectively and both presented in July.A remarkable linear relationship between surface soil microbial carbon and soil microbial nitrogen in growing period was found in larch forest(R2=0.683).The positively correlation between bacteria in soil and N deposition and medium level of nitrogen deposition increased the amounts of actinomycetes and fungi.Different type and different level of nitrogen deposition remarkable affected soil enzyme activity and the influence was complex.6.Based on the field measurements the parameters in the Forest-DNDC model were calibrated and the simulation result of e,e%and MAE were-0.0170,-0.0047,and 1.0176,respectively.The ME value showling linear coincidence degree was 0.8762(R2 = 0.9362).Calibrated models(Forest-DNDC)analysis the carbon and nitrogen cycling characteristics in four climate change scenarios and the results showed climate change will change input and output processes in larch ecosystem in cold temperate zone,decrease the potential of net carbon sequestration,enhance NO and deduce N2O emissions.As a whole,climate change will promote nitrogen storage of larch forest ecosystem. |
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