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Effects Of Forest Conversion From Natural Forest To Plantations Of Soil Carbon And Nitrogen In Subtropical China

Posted on:2019-03-22Degree:MasterType:Thesis
Country:ChinaCandidate:X H HuFull Text:PDF
GTID:2370330548991576Subject:Agricultural Resources and Environment
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Forests are the main part of terrestrial ecosystems.Forest soil carbon stocks are more than two-thirds of global soil carbon stocks.Minor changes in forest soil carbon pools have important effects on CO2 concentration and content in the atmosphere,and thus affect global climate change.Forest conversion is an important way to change land use patterns and is an important driving factor affecting soil carbon and nitrogen cycles.Forest conversion resulted in significant changes in above-ground biomass and litter,which significantly affected soil carbon and nitrogen reserves and conversion processes and enzyme activity.Natural broad-leaved forests are representative vegetation in subtropical regions.With the development of society and economy,commercial forests have been continuously developed,and large-area natural broad-leaved forests have been transformed into economically-purposed commercial plantations.The eighth survey of forest resources shows that the area of artificial forests in China has reached 69.33 million hectares,accounting for 36.3% of the forest land area.In this study,subtropical natural broad-leaved forests and coniferous and broad-leaved mixed forests,Pinus massoniana plantations and Cunninghamia lanceolata plantations were selected as the research objects to investigate the effects of forest conversion on soil carbon and nitrogen content,distribution patterns,enzyme activities and their transformation.The impact of the process include different soil layers(0-20 cm,20-40 cm,40-60 cm),the sub-tropical broad-leaved forests(BL)from and coniferous and broad-leaved mixed forest(CB)converted from natural broad-leaved forests and masson pine The artificial forest(MP)and Chinese fir plantation(CF)soils were used as samples to systematically study the organic carbon and nitrogen contents of different particle sizes,the light organic carbon and nitrogen contents,and the water-soluble organic carbon in the soil after conversion of natural broad-leaved forests to planted forests.Nitrogen content,MBC and MBN content,invertase,urease and catalase activity and soil carbon and nitrogen mineralization.Research indicates:(1)The conversion of natural broad-leaved forests to coniferous and broad-leaved mixed plantations,Pinus massoniana plantations and Cunninghamia lanceolata plantations resulted in a significant decrease in SOC content in 0-20 cm soil layers.The content of soil organic carbon in natural broad-leaved forests was 21.08 g kg-1,the conversion to artificial forest decreased by 19.3%,26.04% and 24.1%;the soil total nitrogen content showed a downward trend,but there was no significant difference between treatments;the litter inventory of broad-leaved forests was 5.25 t hm-2a-1,the others decreased 21.0%,16.8% and 79.4%;With the increase of soil depth,the soil organic carbon and total nitrogen content of the four forest types showed a downward trend.(2)Conversion of natural broad-leaved forests to coniferous and broad-leaved mixed forests,Pinus massoniana plantations,and Chinese fir plantations significantly reduces the CPOC,FPOC and MOC content in 0-20 cm soil layers;natural broadleaved forests were converted to coniferous and broad-leaved mixed plantations and Chinese fir plantations.The correlations between CPOC and SOC were the best in 0-20 cm soil layer,and the MOC and SOC were the best in 40-60 cm soil layer,indicating that soil CPOC could better reflect the impact of forest conversion on surface soil organic carbon;MOC could reflect effects of forest conversion on deep soil organic carbon.The stability of soil organic carbon in natural forest converted to mixed coniferous and broad-leaved plantation and Chinese fir plantation was enhanced,and the stability of organic carbon was reduced when converted to Pinus massoniana plantation.(3)After the conversion of natural broad-leaved forest to coniferous and broadleaved mixed plantation,Pinus massoniana plantation and Cunninghamia lanceolata plantation,the content of WSOC in the 0-20 cm soil layer was significantly reduced and converted into coniferous and broad-leaved mixed plantation.There was no significant change in soil WSOC/SOC in the plantation and the Chinese fir plantation,but in the conversion to Pinus massoniana plantation,the soil WSOC/SOC increased.After the conversion of natural forest to plantation,WSON in different soil layers showed a trend of increasing degree.After conversion of natural forest to plantation,MBC MBN decreased significantly in all soil layers.(4)The soil urease activity increased 72.73%,156.06% and 429.55% after the conversion of natural broad-leaved forests to coniferous and broad-leaved mixed plantations,Pinus massoniana plantations and Cunninghamia lanceolata plantations from 0~20 cm soil layer;the activities of sucrase in mixed coniferous and broad-leaved plantations and Chinese fir plantations decreased by 17.78% and 66.67%,and the conversion to Pinus massoniana plantation increased by 71.11%.(5)The results of culture experiments showed that the rate of organic carbon mineralization in natural forests converted to coniferous and broad-leaved mixed forests and Chinese fir plantations was significantly reduced,and the rate of organic carbon mineralization in converted to Pinus massoniana plantations was significantly higher.The conversion of natural broad-leaved forest to Chinese fir plantation shows a significant increase in the net N mineralization rate,which indicates that conversion of natural broad-leaved forest to Cunninghamia lanceolata plantation promotes the transformation of soil N.
Keywords/Search Tags:Forest conversion, Organic carbon, Enzymatic activity, Mineralization, Natural forest
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