Accumulation And Change Of Soil Organic Carbon Inter-relating With Vegetation Succession In Ziwuling Region

Ziwuling region has developed with various vegetations of secondary forest in Loess Plateau. In different phases of development, vegetation systems in this region have changed from pioneer herbage species initially recovering in abandoned cropping lands (Bothriochloa ischemum, Artenmisia giradii and Stipa bungeana, Artenmisia sacrorum, Spodiopogen sibiricus and Sophora flavecens, Themeda japonica, and Arundinella anomala) to secondary shrubs (Hippophae rhamnoides, Sophora viciifdia, and Ostryopsis davidiana), early forest community (Populus davidiana, Betula platyphylla and Platycladus orientalis with arbors or shrub assembling), and finally Liaotungesis community as the mature forest. In this study, soil profiles (0-5, 5-15, 15-25, 25-35, 35-50 cm soil layers) were selected from typical vegetation systems representing for vegetation successions in the region. Organic C in the soil profiles were measured as in total and fractionated into microbial biomass-C, water-soluble organic-C, light-fraction organic-C, and heavy-fraction organic-C. The amounts of microbial biomass-C, and water content in soil profiles were consistently analyzed. The aim of this study was to investigate interactions between the accumulation of soil organic C and vegetation successions in the region, in a purpose to improve understanding on how changes in soil conditions affect vegetation successions in the region. Main results are summarized as follows.(1) The content of soil organic C in 0-25cm soil layer increases significantly in the course of vegetation succession from abandoned land to Liaotungesis forest community. But the content of soil organic C in >25cm layer doesn't change obviously(3~4g kg-1).The increasing degree of soil organic C is different in the course of vegetation succession. In preliminary vegetation succession from abandoned land community to herbage community, the increasing degree is higher. And with further succession which is herbage-shrub-early forest- Liaotungesisforest community it goes down gradually.(2) The water content in 0-5cm soil layer increases significantly and the water content in > 5cm soil layer decreases in the course of vegetationsuccession. The high significance linear regression between the water content and soil organic matter is discovered( Y=0.1912X, R2=0.3492**). The field capacity and porosity increase gradually and bulk density decrease gradually. The significance linear regression between the field capacity and soil organic matter is discovered as well as porosity and bulk density. This indicates that the accumulation of soil organic matter influences evidently the water holding capacity.(3) The content of microbial biomass-C in 0-15 cm soil layer, the content of the water-soluble organic-C in 0-50cm soil layer, the content of light- fraction organic-C in 0-25cm soil layer, and the content of heavy-fraction organic-C in 0-1 5cm soil layer increase significantly in the course of vegetation succession. With the depth increasing, the content of microbial biomass-C, the content of the water-soluble organic-C, the content of light-fraction organic- C, and the content of heavy- fraction organic-C go down on the soil profiles.(4) The high significance linear regression between microbial biomass-C and soil organic C is discovered( Y=27.978X, R2=0.9498**). Furthermore, the changing degree of microbial biomass-C is remarkably higher than soil organic C. So microbial biomass-C can indicates the change of soil organic-C in the course of vegetation succession.The high significance linear regression between light-fraction organic-C and soil organic-C is also discovered( Y=0.1914X, R2=0.9121*). But the changing degree of light-fraction organic-C is lower than soil organic C. So light-fraction organic-C can not indicates the change of soil organic C in the course of vegetation succession.(5) The high significance linear regression between heavy-fraction soil organic-C and soil organic C is discovered( Y=0.8138X, R2=0.9522**). But the trend of ratio of light- fraction o...