Evolution Characteristics Of Soil Organic Carbon-Structure-Water Enviroment Under Vegetation Restoration On The Ziwuling Maountain,Loess Plateau

Vegetation restoration is the fundamental management to construct ecologicalenvironment in the Loess Plateau, while soil environmental evolution is one of the dominantcontent for ecological effective assessment. To clarify interaction mechanism betweenvegetation restoration process and soil properties, this thesis focuses on typical samples inmain communities of secondary vegetation succession in Loess Plateau. Based on fieldmonitoring and analysis in laboratory, the content and distribution characteristics of organiccarbon in soil profile and aggregate were studied at different stage of vegetation succession. Itprimary showed accumulation and distribution features of soil organic carbon, as well as itssequestration potential, in the process of vegetation succession. By quantitative analysis ofsoil structure, it revealed the soil structure formation, stability and organic carbon transferringprocess and mechanism. Furthermore, combined with monitoring soil moisture characteristicsand dynamic process of water environment, it clearly showed the relationship among soilorganic carbon, structure and moisture characteristics of secondary vegetation restoration inthe Loess Plateau. The main results are shown as following:1. Vegetation restoration promotes soil total organic carbon, components and itssequestration capacityThe results showed that with vegetation succession soil total organic carbon, activeorganic carbon, and passive organic carbon content increased significant in0-100cm soillayer. This increasing trend didn't disappear until herbaceous stage and in climax stage ofsuccession total organic carbon, active organic carbon, and passive organic carbon contentwere5.92kg^-1,1.48kg^-1and4.44kg^-1, respectively. Vegetation restoration enhancing organiccarbon was quite different among its difference composition and we found that total organiccarbon and active organic carbon content promoted significant within70cm soil layer whilepassive organic carbon content increased only within40cm soil layer. However, organiccarbon content changed dramatically in0-5cm soil layer and total organic carbon, activeorganic carbon, passive organic carbon content reached the peak point in climax stage of succession,26.76g kg^-1,8.92g kg^-1and17.83g kg^-1, respectively.With the vegetation succession, carbon density raised obviously. At climax successionstage total organic carbon density was up to6.43kg m^-2; active organic carbon density was1.57kg m^-2and passive organic carbon density was4.86kg m^-2. And we calculated thatvegetation succession play an important role improving organic carbon density within0-40cm soil layer. It is estimated that from the beginning of vegetation restoration to climax stageof succession estimation, practical potential of carbon sequestration in slope farmland,abandoned arable land, herbaceous, shrub and pioneer tree community were2.44kg m^-2,1.55kg m^-2,0.03kg m^-2,0.18kg m^-2and0.19kg m^-2, respectively.2. Vegetation restoration improve soil aggregation effects and structural stabilityWith vegetation community succession,<0.25mm water stable aggregate contentdecreased among different soil layer while>1mm soil aggregate content increased obviously.This represents that it is of beneficial to soil aggregation by vegetation succession. In spatialscale, from the subsoil to topsoil dynamic interaction transferring was represented among soilaggregate with community succession. The property was that micro-aggregate (<0.25mm size)descended gradually while more than2mm aggregate content ascended steadily. All of theseprocesses are good for formation of macro-aggregate.What's more, vegetation succession improved the stability of soil aggregates. We foundthat there was great significant difference of logarithmic function between soil total organiccarbon content and water stable aggregate content(>0.25mm), mean weight diameter ofaggregates and fractal dimension of aggregates. Total organic carbon content was up to15gkg^-1in0-5cm soil layer after slope cropland and0-10cm soil layer of herbaceous community.And the soil structure tended to stable.3. Vegetation restoration changed the content and distribution of aggregates andorganic carbon, and promoted physical protection for soil organic carbonVegetation succession has significant effect on distribution of soil total organic carbon,active organic carbon and passive organic carbon within vegetation communities, soil layersand aggregates. Most of total organic carbon, active organic carbon and passive organiccarbon distributed in0-20cm of topsoil and each of them accounted for75.2%-81.8%,84.6%-90.0%and72.2%-80.6%of0-100cm soil layer. Within different soil layer, especiallyin0-5cm soil layer, organic carbon content was higher than other layer and below40cmdepth of soil there was no obvious difference. Soil profile in different stages of succession, theminimum value of total organic carbon and its composition content existed in aggregateswhich diameter was <0.25mm. The maximum of organic carbon presented in0.5-0.25mmaggregates of0-10cm soil layer. Below10cm depth, however, the maximum value of soil total and passive organic carbon content was in aggregates which diameter are>2mm whileactive organic carbon almost was in>5mm aggregates.Contribution of total organic carbon, active organic carbon and passive organic carbonpresented similar features in temporal (community succession) and spatial (from subsoil totopsoil) scale. It revealed that diameter less than0.25mm aggregates contributed less andless but over than2mm diameter aggregates contributed more and more with the process ofsuccession. To be more specific, lager aggregates contributed most in herbaceous community.This indicates that physical protection of organic carbon in aggregates increased from smallparticle size (<0.25mm size), via intermediate size (2-0.25mm), and ultimately to largeparticle (>5mm). Therefore, this dynamic transferring process was good for protectionorganic carbon by soil aggregation.4. Vegetation restoration improved soil pore characteristics and soil moistureWith the succession of vegetation communities, the whole bulk density of soil profilegradually decreased until the climax succession stage, which was only1.16g cm-3. And itwas clear that bulk density reduced rapidly in0-5cm depth of soil. By contrast, total porosityof soil profile increased steadily and was up to max value at the climax community, whichdepth was available to40cm. For the soil layer of0-20cm, soil total porosity, aerationporosity and capillary porosity ascended significantly, soil total porosity reached maximumvalue in the stages of the pioneer arbor forest and the climax community within0-5cm soillayer,79.67%and73.86%, respectively. To be more specific, soil capillary porosity was up to20%at the climate community stage, and soil aeration porosity in the pioneer arbor forestreached up to43.57%.The soil water retention enhanced gradually during the succession of vegetationcommunities, which was mainly at0-40cm soil layer. This trend was more obviously in0-5cm soil layer and the strongest performance of water retention appeared in climax communitystage. The whole water supply capacity of soil profile also improved gradually withvegetation succession, and this was vividly shown at0-20cm soil layer.Vegetation restoration improved saturated hydraulic conductivity of soil profile, and thisfeature expanded to shrub community even to40cm depth of soil. It can be observed in0-10cm and in climax community stage soil saturated hydraulic conductivity was at thehighest point, up to138.0mm h-1.Using CT (X-ray scanning computed-tomography) method, we noticed that vegetationrestoration could significantly improve parameters characteristics of soil macrospore in0-5cm soil layer. This interaction enhanced gradually during the succession of vegetationcommunities. There was linear relationship between soil organic matter and each pore parameter and bulk density. Therefore, the main driving force for improvement of surface soilpore and infiltration characteristics is the accumulation of soil organic matter during theprocess of vegetation restoration.5. Vegetation restoration improved the soil water storage function and soil watermicroenvironmentBased on continuous monitoring mean value of water consumption and precipitation forthree years(wet year-normal year-dry year), the results showed that water consumption wasas following: herb community (641.5mm)> thickets community (554.2mm)> pioneer arborcommunity (512.7mm)> climax community (502.7mm). Furthermore, we calculated that theaverage precipitation was612.2mm during the growth period and found that waterconsumption was lower than rainfall except for but herb community. In pioneer arborcommunity and the climax community, vegetation ability to adapt environment promotedobviously.After three continuous growing seasons, the volume of soil water recovery in allvegetation communities showed that: climax community (244.9mm)> pioneer arborcommunity (201.6mm)> thickets community (97.7mm). In abandoned land and herbcommunity, however, soil water recovery volume was negative. This means which soil waterenvironment obviously improved in the climax community stage.After comprehensive analysis of the relationship between soil properties and soil waterrecovery, we considered that soil organic matter accumulation,soil structure and watercharacteristics indexes improved were dominant factors for restoration and enhancing soilwater environment.>0.25mm of soil water stable aggregate content and soil water retentionhad significant promotion for improvement of soil water storage in0-500cm soil layer.