Impacts Of Nitrogen Deposition On Carbon Pools And Carbon Sequestration Benefits In The Chinese Fir Plantation

Now forest carbon sink function is considered as the best economical and efficient method toslow global warming. As a popular afforestation tree species, Chinese fir plantations are widelycultivated in China because of fast growth rate with high ecological function of atmospheric CO2sequestration and the economic value. In recent years, the increasing atmospheric nitrogen depositiongreatly affects forest sink/source dynamic and the sustainable development of forest under thelow-carbon economy. Southern China has become the third largest nitrogen deposition regionfollowing the United States and Europe area, so it is needed to research the effects of nitrogendeposition on carbon sequestration and the economic benefits in forest ecosystems. These studies canprovide scientific basis for comprehensive understanding of the relationships between nitrogendeposition and terrestrial ecosystem carbon sequestration.In this thesis, simulated nitrogen deposition experiment was conducted in a Chinese firplantation with four treatment levels, which were N0(0kg N hm^-2a^-1)、N1(60kg N hm^-2a^-1)、N2(120kg N hm^-2a^-1)、N3(240kg N hm^-2a^-1) respectively. After8years of nitrogen treatment, we measuredand analyzed the ecosystem carbon pools in trees, understory plants, forest floor and soil. The resultsshowed that forest carbon stocks increased with the increase in the amount of nitrogen deposition withthe values of93.48、94.75、98.61、99.63t C hm^-2respectively under N0、N1、N2、N3treatment.Understory vegetation carbon stocks decreased significantly under nitrogen deposition, comparedwith the control （N0）, N1、N2、N3treatments decreased carbon stocks by68.57%、84.29%and87.14%, respectively. Nitrogen deposition significant inhibited the understory plant growth. Carbonstocks in the forest floor increased by193.27%,83.97%and35.89%, respectively, under N1、N2、N3treatments, and the same trend was found in both L and F layers. Organic carbon storage in soil （0-60cm） are85.68、89.45、88.88、80.59t·hm^-2along with nitrogen treatment, indicating that medium andlow nitrogen treatment can promote soil carbon storage while high nitrogen treatment decreased thecarbon storage.The results showed that forest carbon storage was highest carbon pool among the componentsand accounted for50.44%～54.77%of total ecosystem carbon storage. Soil was the second largestpool and accounted for44.30%⁴7.62%. The samllest carbon pool was forest floor and onlyaccounted for0.05%⁰.39%. In conclusion, medium and low nitrogen treatments increased theecosystem carbon storage in both plants and soil. High nitrogen treatment increased plant carbonstorage, but was offset by the negative effects on soil carbon storage, resulting in a marginal effect.The economic values of ecosystem carbon sequestration increased by1717、2195and219$·hm^-2,respectively, under N1、N2、N3treatments when using afforestation method. However, the economicvalue were8504、10869and1084$·hm^-2, respectively, by carbon tax law.