Effects Of Land Use On Soil Organic Carbon And Aggregate In Karst

With the deepening studies of global change,global carbon cycle research has become one of the three major hot spots about the global change research,which is also the current frontier field of the Earth Science.The carbon cycle of terrestrial ecosystems plays an important role in the global carbon balance.Soil carbon pool is the largest carbon pool in terrestrial ecosystems,which is the important link of global carbon cycle. It is extremely sensitive to the response of land use change,which can be regulated in a shorter time.In general,it is in favor of improving the stability of soil aggregates that soil organic carbon participates in the formation of aggregates.The study on the influence of land use on soil organic carbon,its components and aggregates can further reveal the role of soil organic carbon and its components in the formation and stability of aggregates in karst area.At the same time,it has an important theoretical and practical significance on the regulation of the sources or sinks of CO₂ and increase of the ability of storage agricultural soil carbon.In this study,the five typical land use patterns are collected from Zhongliang mountain karst valley,they were vegetable land,grassland,farmland,orangery and shrub.The main contents contain field investigation and soil sampling,lab experiments and analysis.The processes as follows:Firstly,the of soil organic carbon and its components,soil physical and chemical properties(aggregate stability,soil bulk density, soil moisture content and soil nutrients) were measured in the five typical patterns of land use.Secondly,the composition of soil organic carbon were analyzed,which include soil microbial biomass carbon,mineralizable carbon and soil K₂SO₄-soluble carbon.Thirdly,the response characteristics of soil organic carbon and its component to land use are discussed.Fourthly,the stability and preservation probability of soil aggregate in all kinds of sizes by transfer-matrix method and how to response for land use were analyzed,The Last but not least,the relationship of the stability index and preservation probability of soil organic carbon and soil aggregate in all kinds of sizes are discussed by path coefficient analysis.The stability of soil aggregates is strongly influenced by land use patterns.The order of stability index as follows:the grassland＞shrub＞Orangery＞farmland＞vegetable land.The stability of soil aggregates is much higher under natural land use patterns,but it is lower,which are obvious disturbed by human activities such vegetable land and farmland..The preservation probability of soilaggregate in all kinds of sizes is obviously influenced by land use patterns.The preservation probability of soil aggregate in size of 0.25-1mm reduces,but that more than 1mm obviously increases in grassland.Meanwhile,that in size of 1mm obviously increases in 3-2mm and 2-1mm also improves in shrub.In general,the size of soil aggregate is much smaller,the preservation probability is more higher in farmland and vegetable land.Contrast with farmland and vegetable land,the preservation probability in size of 3-1mm increases in orangery.The stability of soil aggregate has distinct change in vertical direction in farmland under different land use patterns.With the increasing of soil layer thickness, the stability of soil aggregates reduced in the shrub and grassland.And with increasing of the soil layer thickness,the stability of aggregate improved in the orangery and vegetable land.However,the stability of soil aggregate has no obvious change in vertical distribution in farmland.The composition of soil organic carbon fractions is significantly affected by land use patterns.The order of soil microbial content is:grassland＞shrub＞Orangery＞farmland＞vegetable land.The measurement of microbial quotient follows by vegetable land＞Orangery＞farmland＞grassland＞shrub.The content of mineralizable carbon as follows:orangery＞vegetable land＞farmland＞shrub＞grassland.At the meantime, the vertical distribution trend of soil organic carbon and its composition in the soil profile is also influenced by land use patterns.The soil microbial carbon and microbial quotient are sensitive response within the range of 0-30cm.Meanwhile,the content of soil organic carbon,mineralizable carbon and soil K₂SO₄-soluble carbon reduced with soil depth increasing in the soil profile.The results show that microbial quotient can reasonable and sensitive to the response of soil organic carbon pools on land-use response.The factors are more complicated,which impact soil organic carbon and its components.The results show that there is a necessarily positive correlation among soil organic carbon content and soil microbial biomass carbon and soil mineralizable carbon (P＜0.01),and there is also a necessarily positive correlation among microbial biomass carbon and soil mineralization carbon and potassium extraction as well as microbial quotient(P＜0.01).Soil microbial biomass carbon has a significant positive correlation with total nitrogen and has a significant negative correlation with available phosphorus;However,there is on obvious correlation between microbial quotient and soil nutrients;At the same time,a significant correlations have been found among available potassium,soil organic carbon Soil K₂SO₄-soluble carbon and total nitrogen, hydrolysable N and available K.potassium Baptist to carbon and total nitrogen and hydrolysable nitrogen have necessarily positive relations,and has positive relation with available K.The sand(1-0.05mm) has a visible impaction on soil organic carbon and its content of composition and distribution.The research about the relationship between components of soil organic carbon and soil aggregate under different land use patterns show that there is no necessarily positive relation between components of soil organic carbon content and the stability index of soil aggregate,which is strongly related to natural land use.Meanwhile,the relation of soil organic carbon and its component,the stability index of soil aggregate,and the preservation probability of soil aggregate in all kinds of sizes are discussed by path coefficient analysis.The results showed that the preservation probability(＞3mm) has an obviously influence on the content of soil organic carbon and soil mineralized carbon. Soil aggregates of 0.5-3mm promote microbial activity and increase the content of soil microbial biomass in the soil.The preservation probability of soil aggregate in size of 1-5mm has intimately relationship with Soil K₂SO₄-soluble,and soil microbial quotient has close relationship with the preservation probability of soil aggregate in size of 1-5mm.