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Responses Of Aggregate Stability And Organic Carbon In Two Parent Rock Soils To Forest Conversion In Mid-subtropical Mountain Areas Of China

Posted on:2016-03-06Degree:MasterType:Thesis
Country:ChinaCandidate:X H WangFull Text:PDF
GTID:2480304715489414Subject:Physical geography
Abstract/Summary:PDF Full Text Request
As the largest carbon pool and the main source and sink of carbon sequestration in the terrestrial ecosystem,soil play an important role in the global carbon cycling.Forest soil is the main component of soil carbon pool stored about 70%of soil organic carbon,and it was 2-3 times of forest biomass carbon pool and L4 times of atmosphere carbon pool,a little change of forest soil carbon pool would induce a significant impact on the concentration of CO2 in atmosphere.The researches on forest soil carbon cycle have profound significance under the background that global warming has been an inevitably fact Soil aggregate has regarded as an important mechanism of soil organic carbon(SOC)stability due to it provides physical protection for SOC from microbial decomposite,above 70%SOC was sequestrated in micro-aggregates in forest mineral soil.Meanwhile,as the essential unit of soil structure,soil aggregates affect the water permeability,water retention capability and anti-erode capability of soil,and play an important roles in regulating soil fertility and maintaining soil productivity.Researches of soil aggregate stability and aggregate associated organic carbon has gained more and more attentions.The evergreen broad-leaved forest in mid-subtropical China is noted by its highly biomass and productivity,and plays an important role in global terrestrial ecosystem carbon sequestrattion,it is also the unique and an important forest type at the same latitudinal zone on the earth.Large area of native broad-leaved forests have been cleared and converted to pure plantations,which have significantly altered the structure,function and landscape patterns of mountain region,as well as the soil-plant-atmosphere interaction processes.However,the responses and feedback of soils developed from different rock to forest conversion remain unclear,which was a key content need to resolve for better understanding of forest soil structure and forest carbon cycle in this region.This study selected native Castanopsis carlesii forest(NF),Castanopsis carlesii plantation(CC)and plantation(CF)which were converted from NF Background conditions of these forests was consistent and soil were developed from granite rock in Chenda state owned tending forest farm,Sangming,Fujian province,and the same type of forests but soil were developed from sandstone rock in Castanopsis kawakamii nature reserve area,Sangming city.The responses of soil aggregate stability,size distribution and mineralization of aggregate associated organic carbon,and organic carbon fraction to forest conversion under soils developed from different parent rock were determined.This study will provide basic data and support for further researches of the impact mechanism of forest conversion on soil carbon sequestration in mid-subtropical region,and give a new thought for forest managements to modulate and improve the capability of soil as carbon sinkResults showed that forest conversion had strongly affect soil aggregate stability,organic carbon size distribution and mineralization,and carbon fraction,however,the feedbacks of granite soils and sandstone soils were different.NF converted to CC and CF induced>0.25 mm water-stable aggregates decreased 8%and 14%as well as MWD decreased 0.3 and 0.5 mm on average,respectively.The amount of>2 mm macro-aggregates and aggregate stability in granite soils were higher than in sandstone soils.In granite soils,relationships of total soil organic carbon content,clay content,selected extractable Fe and Al oxides and aggregate stability were significant and positive.However,only total soil organic carbon content had significant and positive correlation with aggregate stability in sandstone soils.After forest conversion,aggregate associated organic carbon content declined with increasing disturbance intension.For example,contents of>2 mm and 0.25-2 mm aggregate organic carbon decreased 39.93%and 54.34%on average in sandstone soils,respectively and>2 mm,0.25-2 mm,0.053-0.25 mm and<0.053 mm aggregate organic carbon dropped 23.53%,24.85%,27.57%and 14.73%on average in granite soils,respectively.The contribution of aggregate organic carbon to SOC ranged from 66.88%to 94.50%.0.25-2 mm aggregates was the main component which contributed 39.27%-46.11%to SOC in sandstone soils,but the differences of the contribution of>2 mm and 0.25-2 mm aggregates to SOC were not significant.Forest conversion resulted in increased contribution of organic carbon in aggregates to SOC.Cumulative CO2 mineralization in aggregates decreased with decreasing size and increasing disturbance.Cumulative CO2 mineralization of>2 mm,0.25-2 mm and 0.053-0.25 mm in granite soils were 1,17,1.33 and 1.57 times higher than in sandstone soils.Unprotected organic carbon fractions(light fraction and particulate organic carbon)had declined to different extents after forest conversion.Especially the fine particulate organic carbon(fPOC)in sandstone soils and coarse particulate organic carbon(cPOC)in granite soils were responsed to forest convertion sensitively,but the minimum declined was occurred in mineral-associated organic carbon fraction(mSOC).When NF was converted to CC and CF,SOC loss in sandstone soil was concentrated on fPOC which declined 35%and 53%,accounted for 51%and 48%of SOC loss,respectively.In contrast,the main SOC loss in granite soil was mSOC which declined 19%and 21%,accounted for 49%and 51%of SOC loss,respectively.
Keywords/Search Tags:parent rock, forest conversion, water-stable aggregates, stability, organic carbon, carbon fraction
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