Characteristics Of Enzyme Activities And Active Fractions Of Soil Organic Carbon Under Different Vegetation Types In Loess Hilly Of North Shaanxi

In order to research the soil quality conditions under different vegetation types and the effects of vegetation restoration on stability of soil enzyme activities and fractions of organic carbon pool in Loess Plateau after revegetation, we selected the soil samples of 0-5cm and 5-20 cm layers under different vegetation types(Forest, Forest steppe, Grassland, Sandland, Desert) in Loess Hilly of north Shaanxi as research objects, through investigating the distribution characteristics of soil active organic carbon components and enzyme activities under different vegetation types, revealing the distribution regularity of soil active organic carbon and enzyme activities under different vegetation types in loess plateau, trying to provide theoretical basis for the influences of soil carbon cycle and vegetation restoration on fractions of organic carbon, enzyme activities and its stability. The main conclusions are as follows:(1)Different vegetation types had different effects on the distribution regularity of soil physical and chemical properties. The results showed that soil bulk density and p H content presented a trend that maximum in desert and sandland vegetation, followed by grassland and forest steppe vegetation, and the forest vegetation was lowest. Soil available K, total N and moisture content presented a decreasing trend that forest > forest steppe > grassland >sandland and desert, and as to the soil total N and moisture content, there were no significant differences in different soil layers for the same vegetation type, but the opposite phenomenon was found for the available K. Soil available P, total P, NH4+-N and NO3-N presented a trend and chemical properties between the two vegetation types.(2)Vegetation restoration and reconstruction could promote the accumulation of soil organic carbon, and the distribution regularity of soil active organic carbon under different vegetation types were different. Compared with the forest steppe, grassland, sandland and desert vegetation types, in 0-5 and 5-20 cm soil layers of forest vegetantion type, the soil microbial biomass carbon content increased by 211.19, 145.32 mg?kg-1,376.90, 217.95 mg?kg-1,480.66, 272.39 mg?kg-1,478.61, 280.28 mg?kg-1, respectively, and the total content of soil easily oxidized organic carbon were 4.26, 4.78, 33.21, 9.41 times that of others, respectively, and the soil dissolved organic carbon content were 1.38, 1.39, 1.80, 1.29, 15.41, 15.91, 13.50, 11.60 times that of others, respectviely. Soil active organic carbon presented a trend that maximum in forest, followed by forest steppe and grassland vegetation, and the desert and sandland vegetation were lowest, and its Content decreased gradually from south to north. Soil microbial entropy in 0-5 and 5-20 cm soil layers ranged in 0.0087- 0.0157 and 0.0049- 0.0049, respectively, and presented a decreasing trend that forest,forest steppe,grassland>sandland, desert. There were significantly positive correlations between soil organic carbon and components of active organic carbon, microbial entropy, it demonstrated that active organic carbon and microbial entropy were largely affected by soil organic carbon content. Compared with the soil oxidation organic carbon and organic carbon, Soil microbial biomass carbon and dissolved organic carbon were more sensitive to the change of environment.(3) Soil urease activity, invertase activity and alkaline phosphatase activity showed significant difference except for the sandland and desert vegetation. Soil urease activity, invertase activity and alkaline phosphatase activity of forest, forest steppe, grassland, sandland and desert vegetation were 3.02, 2.27, 1.63, 0.46, 0.24 mg?g-1?24-1,42.03, 27.50, 21.40, 4.03, 6.19 mg?g-1?24-1,7.51, 6.42, 3.58, 0.58, 0.51 mg?g-1?24-1, respectively, and presented a decreasing trend that forest > forest steppe > grassland > sandland, desert vegetation types. Enzyme activities in upper and lower soil layers of forest, forest grassland and grassland vegetation types differed significantly, and the difference was higher in 0-5 cm and the content decreased with increasing soil layer. Soil enzyme activities were largely influenced by soil nutrient and soil nutrients could promote the generation of enzyme activity. Soil urease, invertase and alkaline phosphatase activity influenced and related each other closely.(4) In a certain range of latitude, with the latitude increasing, soil organic carbon, microbial biomass carbon, easily oxidized organic carbon and dissolved organic carbon in the upper and lower soil layers both presented a trend that first decreasing significantly and then increasing slightly and last decreasing. Compared with the spatial variability in the upper and lower soil layers of soil organic carbon, microbial biomass carbon and dissolved organic carbon, soil layer of easily oxidized organic carbon was lower and the range of variation in the 0-5 cm was higher than 5-20 cm. It demonstrated that the sensitivity of soil active organic carbon to the variation of latitude in 0-5 cm was higher than that in 5-20 cm.(5) With the range of latitude in this paper, soil urease, invertase and alkaline phosphatase activities significantly reduced with the increasing latitude. The spatial variability of enzyme activities in 0-5 cm was slightly lower than that in 5-20 cm, and compared with soil urease activity and invertase activity, the spatial variability of alkaline phosphatase activity was significant lower, The spatial distribution of phosphorus was homogeneous which contributed to the slighter spatial variability of alkaline phosphatase. The sensitivity of enzyme activity to the variation of latitude in 0-5 cm was consistant with that in 5-20 cm.(6) Canonical analysis between soil active organic carbon and enzyme activity and soil nutrient showed the relationship that the activity of urease and invertase were influenced by the content of soil dissolved organic carbon, microbial biomass carbon easily oxidized organic carbon had no significant effects on it. The content of total P and available P significant influenced activity of alkaline phosphatase. Soil organic carbon had significant effect on moisture content and total P. Person correlation analysis showed the content of soil active organic carbon greatly depended on the soil organic carbon, soil organic carbon and active organic carbon had larger influence on the soil enzyme activity, the impact of soil nutrients on the enzyme activity was related to the types of soil nutrients, but all kinds of soil nutrients significantly correlated with enzyme activity.