| Located in the arid and semi-arid areas, Loess Plateau has fragile ecosystems, serioussoil erosion and severe loss of soil organic carbon pool. Vegetation recovery become animportant way to control soil erosion and improve soil organic carbon reserves. As animportant biotic factor, vegetation affect the amount of soil organic matter inputs; and controlthe decomposition and transformation processes of those inputs due to their biochemistrycharacteristics. Soil moisture, the basic need for the survival of earth lives, places a directimpact on vegetation growth and development and an indirectly impact on the formation,decomposition and migration of soil organic matter. Therefore, vegetation water status andsoil organic carbon accumulation might share a certain coupling relationship in the arid andsemi-arid area.We selected typical small watershed of Hilly Region of Loess Plateau, and investigatedSOC, soil moisture and root distribution after vegetation restoration （cropland-grassland-woodland）. Collected data after field sampling and laboratory analysis, used classicalstatistical methods （Variance Analysis, Mean Comparison, Correlation Analysis, RegressionAnalysis） to assess the following aspects:（1） Different slope positions （valley bottom, gullyslope and hilly slope） and different land uses （woodland, grassland and farmland） on SOC andsoil moisture spatial distribution at small watershed scale,（2） SOC, soil moisture content, fineroot distribution characteristics and their mutual relationship after vegetation restoration ofsmall catchment in Loess Plateau.Obtained the following main results:（1） Converting farmland to woodland and grassland could improve SOC at thesurface（0-20cm）. SOC content of farmland was3.11g kg-1at the gully slope, woodland andgrassland6.22g kg-1and5.09g kg-1respectively, increased by100%and64%than farmland.SOC content of farmland was3.87g kg-1at the gully slope, woodland and grassland4.17gkg-1,3.95g, kg-1respectively, increased by only8%and2%than farmland. Obviouslywoodland produced more SOC than grassland. Grassland SOC were higher than farmland atgully slope（20-100cm）. Contrary to the hilly slope, farmland SOC were higher than that ofwoodland and grassland. Of either woodland or grassland, gully slope SOC content was higher than the hilly slope, increased by49%and29%, respectively（0-20cm）.（2） Vegetation recovery also had a significant impact on soil moisture. Mean soilmoisture content of the profile （0-100cm） at valley bottom was the highest, followed by gullyslope and hilly slope. Woodland, grassland both decreased water content compared tofarmland, with woodland the lowest mean water content. Check dam soil moisture showed theregular fluctuations and layered distribution; loessial soil moisture content first increased atshallow layer （0-100cm） and then decreased slightly with soil depth increasing; aeolian sandysoil moisture changed in larger magnitude, and the overall soil moisture （0-600cm） decreased.（3） Fine root biomass varied among different vegetation types. Soil moisture, SOC andfine root biomass showed significant change along soil depth（0-100cm）, SOC and fine rootbiomass reduced with soil depth, while soil moisture increased. Fine root biomass of The10sampled vegetation communities were mainly allocated at the surface layer（0-40cm）, andrelatively rare below40cm.（4） At the same slope position, soil water storage decreased with the increasing fine rootbiomass, while SOC reserves increased. Regression analysis showed that fine root biomass ofthe entire1m profile significantly affected soil water storage. It could explained the variationof soil water storage up to94%. Fine root biomass showed closer relationship to SOCreserves at the surface layer （0-40cm）, and could explained72%of the SOC variability.Considering the effects of vegetation roots, soil water storage and SOC storage showedsignificant negative correlation.Vegetation restoration brought more organic matter to soil, but soil water storage wasseverely consumed. Soil moisture extremely limits vegetation growth in most parts of LoessPlateau, thus improving water use efficiency is the fundamental urgency to increase theamount of organic matter input. Therefore, how to properly use limited precipitation toimprove the efficiency of soil moisture utilization has become a key measure to increase SOC.Although this study has achieved worthy results, many tough problems remains to solve. It isdifficult to determine soil moisture due to its strong variability with only limited datacollected once or twice in the field. It is necessary to set the runoff experimental plots tocontinuous observe Temporal and spatial variation of soil moisture. Additional cultivationexperiments should be conducted to test the impact of moisture on organic carbondecomposition and transformation processes. |
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