| Changting County was one of the most severe reddish soil erosion regions in South China.Because of its characteristics of drought tolerance,poor tolerance,and strong adaptability,Pinus massoniana was used as the main afforestation tree in the treatment of reddish soil erosion regions in the Changting,forming a large area of pure Pinus massoniana forest in the preliminary treatment area of reddish soil erosion regions.Although the soil erosion in these erosion areas has been suppressed to a certain extent,there are still a series of ecological problems such as single tree species,low species diversity,soil erosion under forest,and weak stand resistance.In the early stage of the research group,research on the transformation of broad-leaved species of Pinus massoniana in the eroded area of Changting reddish soil erosion regions was carried out.A series of studies were carried out on the effects of different thinning intensity on the soil erosion and vegetation restoration of different broad-leaved species of Pinus massoniana forest.However,there are few studies on the carbon and nitrogen cycling in the Pinus massoniana forest ecosystem.In particular,the input,storage,export,and recycling processes of carbon and nitrogen in the canopy forest ecosystem of different canopy levels are still unclear,it failed to fundamentally solve the ecological problems in the ecosystem of Pinus massoniana.The carbon cycle and nitrogen cycle are key processes that drive changes in forest ecosystems and have important implications for global climate change.Through the study of carbon and nitrogen cycling processes in different canopy density of Pinus massoniana forest ecosystems,the differences in carbon and nitrogen cycling processes of Pinus massoniana forests with different canopy levels were compared.The influence of canopy density on the carbon and nitrogen cycle of Pinus massoniana forest ecosystem was analyzed to construct the ecology of Pinus massoniana forest.The compartmental model of the carbon and nitrogen cycle of the system reveals the process of carbon and nitrogen cycling in forest ecosystems and the impact mechanism during the treatment of reddish soil erosion regions in Changting.Provide technical support for soil erosion control and ecological civilization construction in reddish soil erosion regions in Changting.Therefore,this paper takes the typical representative of erosion soil in southern reddish soil erosion regions of Changting County as the study object,and establishes standard runoff plots of Pinus massoniana forest with different canopy density.The carbon and nitrogen contents of different ecosystem components such as atmospheric deposition,stemflow,throughfall,decomposition of litter,runoff and sediment loss,forest soil,etc.in Pinus massoniana forest were compared among different compartments of Pinus massoniana forest ecosystem.Based on the differences in carbon and nitrogen input,output,and storage,the impact of canopy density on the carbon and nitrogen cycle of Pinus massoniana forest ecosystem was analyzed.The carbon and nitrogen cycle compartment model of Pinus massoniana forest ecosystem in the eroded area of Changting reddish soil erosion regions was constructed to reveal the ecology of Pinus massoniana forest in the red soil erosion area.The carbon and nitrogen cycle of the system provides a scientific basis for improving the ecological function of the Pinus massoniana forest ecosystem.The major results were as follows:(1)There are differences in carbon and nitrogen inputs in the atmospheric deposition of Pinus massoniana forest ecosystems in different canopy areas of Changting red soil.The input of carbon and nitrogen in the stemflow was gradually increasing with the increase of canopy density of Pinus massoniana forest,while the input amount of carbon and nitrogen in the penetrating rain was opposite,and decreased with the increase of canopy density.(2)With the increase of canopy density of Pinus massoniana forest,the aboveground biomass and carbon and nitrogen storage of Pinus massoniana showed a trend of increasing first and then decreasing,and reached the maximum at canopy density of 0.6.The changes of nitrogen storage showed the same pattern as that of Pinus massoniana forest,but the root carbon and nitrogen storage decreased with the increase of canopy density of Pinus massoniana forest.The increase in canopy density of litter carbon and nitrogen storage forests in Pinus massoniana forests first increased and then decreased,reaching the maximum at canopy density of 0.6;the litter mass,carbon and nitrogen storage of Pinus massoniana were the same in canopy density.Showed as leaves>other>flowers and fruits>bark>branches.(3)With the increase of the canopy density of the Pinus massoniana,the carbon and nitrogen storage in the 0-10 cm soil layer of the woodland increased first and then decreased,and reached the maximum when the canopy density was 0.6,but the storage of carbon and nitrogen in the 10-20 cm and 20-40 cm soil layers was not obvious with the canopy density,and the total storage of soil carbon and nitrogen was in accordance with the change law of the surface soil.It shows that the influence of canopy density on soil carbon and nitrogen is mainly on the surface of the soil.(4)The loss of carbon and nitrogen in the ecologic system of Pinus massoniana first decreased with the increase of canopy density,and reached the minimum at 0.6 of the canopy density,and the loss of carbon and nitrogen gradually increased with the increase of the canopy density.(5)Under the same canopy density,the storage of carbon and nitrogen in the Pinus massoniana forest ecosystem was the highest in the soil compartments,followed by the plant sub-compartments,followed by the root partitions and the litter compartments;the soil compartments and the plant grounds were under different canopy densitys.The storage of carbon and nitrogen in some sub-compartments,root sub-chambers and litter sub-chambers showed a tendency of increasing first and then decreasing with the increase of canopy density,and it was the largest at canopy density of 0.6.(6)During the biological cycle of the Pinus massoniana forest ecosystem,the absorption,retention and return of carbon and nitrogen in the Pinus massoniana forest increased first and then decreased with the increase of the canopy density,and the cycle coefficient of carbon and nitrogen reached the maximum when the canopy density was 0.6,and the cycle coefficient gradually decreased with the increase of the canopy density.During the cycling process,the net accumulation of carbon and nitrogen increased first and then decreased with the increase of stand density.When the canopy density was 0.6,the net accumulation was the largest.In summary,the storage of carbon and nitrogen in Pinus massoniana forest ecosystem in the eroded area of Changting reddish soil increased first and then decreased with the increase of canopy density,and reached the maximum at the canopy density of 0.6,and then gradually decreased.From the perspective of ecosystem carbon and nitrogen cycle analysis,the canopy density of Pinus massoniana forest stands at its 'threshold',and exceeding this 'threshold' is not conducive to the storage of carbon and nitrogen in the ecosystem. |
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