| Took Mu Us sand land in the agro-pastoral transition zone of Northern China as example, based on the theories of soil genetic science, land resource and restoration ecology, through field surveying data and indoor analyzing, we studied the properties of soil physical and chemical characteristics during vegetation restoration. The main results we got are as follows:(1) Both vegetation coverage and above ground biomass increased significantly during the natural restoration process. Species richness index and diversity index decreased through the restoration stages. However, the evenness index tended to increase as vegetation became sparse. Soil domain particle changes from sand to a combination of fine sand and silt and clay. Soil organic matter content and other nutrients increased during the restoration process and soil fraction dimension increased as well. There was a significant negative linear correlation between Dm and sand content; and significant positive linear correlations between Dm and silt and clay contents, organic matter, total nitrogen, available N, P, K concentrations, and CEC and CaCO3 concentrations. However, there was no correlation between Dm and pH. Path analysis showed that soil organic matter, available K and CaCO3 had a positive direct effect on urease activity, soil organic matter, total nitrogen, available N and CEC had a positive direct effect on alkaline phosphatase activity and soil organic matter, available P, available K and CEC had a positive direct effect on invertase activity. Principal component analysis showed that during the restoration process soil quality turned to be better and the extent of desertification reduced gradually.(2) Sand content in the bare land was the highest, fine sand content in shrub was highest whilst silt content in arbor was highest and clay content in grass land was highest of the four artificial forests. Soil organic matter, total N, P, K, available N, P, K contents showed the same trend that was arbor land > grass land > bush land > bare land, and there was significant difference between them. There was no difference between soil mineral elements K2O and Al2O3. MgO content in arbor land was highest, Fe2O3 and TiO2 contents were in turn arbor land > grass land > bush land> bare land and MnO and CaO contents was highest in arbor land and grass land, bush land was the second and lowest in bare land. Soil catalase activity in soil profile showed a turn like arbor land > grass land≈bush land, alkaline phosphatase activity showed like bush land > arbor land > grass land, urease activity showed like arbor land > bush land > grass land and invertase activity showed like arbor land > grass land >bush land. Correlation analysis showed that there were significant positive correlation between soil alkaline phosphatase activity and soil organic matter, total nitrogen, available nitrogen and total potassium. Soil urease activity was significantly positively correlated with soil organic matter, total nitrogen, available phosphorous and CEC. Soil invertase activity was significantly positively correlated with soil organic matter, total nitrogen, available nitrogen and CEC. There were significant positive correlations among the three enzymes.(3) Along the chronosequence the fine sand content increased from 0 year abandoned land by 12.3%, 21.6%, 30.5%, 37.6%, 67.4%, 77.0%, and 86.4% for the sites representing 5, 10, 15, 25, 30, 40, and 50-year reforestation histories, respectively and it showed significant difference among the eight sites from LSD test. With the increasing of years revegetation, soil nutrients increased, while it decreased with the depth. Following reforestation, soil fine sand, SOM, TN, available N, TP, available P and available K increased as a polynomial function of years vegetation restoration while soil silt and clay contents increased as a power l function of years vegetation restoration.(4) Soil organic matter content and nutrients in 11years caragana korshinskii was highest than 6years and 17years caragana korshinskii. The contents of SOM increased dramatically in ripe Pinus tabulaeformis and Robinia psendoacacia. The contents of SOM and nutrients were higher in Robinia psendoacacia than that in Pinus tabulaeformis of the same age.(5) From the central desertified area to the southeast area, soil organic matter and nutrients increased and soil quality increased as well.(6) With the increase of plant coverage, soil sand content decreased and silt and clay contents increased. Compared to 0% plant coverage soil sand content of 90% plant coverage decreased 229.1%, soil silt and clay contents increased 28.3 times and 4.65 times, soil organic matter content increased 14.53 times and soil total nitrogen, available nitrogen, available phosphorous, available potassium, CEC and CaCO3 increased 16.75times, 21.1 times, 3.5 times, 32.6 times, 12.4 times and 1.02 times, respectively. Soil SOM and nutrients increased as a polynomial function with plant coverage.(7) Restricted grazing regimes affected soil restoration strongly. Soil physicochemical properties of 6 years restricted grazing was much higher than that of 2 years restricted grazing and normal grazing land.(8) Soil physicochemical properties of different revegetation pattern showed great difference. In the 0-20 cm layer, soil silt content of caragana microphylla was 289.2% higher than that of CK. The clay content of mixed forest of Robinia psendoacacia and amorpha fruticosa was 55.6% higher than that of CK. Soil organic matter, total N, P, K and available N, P, K concentrations of mixed forest of Robinia psendoacacia and amorpha fruticosa were significantly higher than that of others. Soil catalase activity and urease activity of mixed forest of Robinia psendoacacia and amorpha fruticosa were highest while soil alkaline phosphatase activity and invertase activity of mixed forest of Pinus tabulaeformis and amorpha fruticosa. Soil sand content was significantly negatively correlated with soil alkaline phosphatase activity, urease activity and invertase activity while soil SOM, total N, P, K and available N, P, K, CEC and CaCO3 were significantly positively correlated with soil alkaline phosphatase activity, urease activity and invertase activity. Soil catalase activity was significantly positively correlated with soil SOM, total N, P, K and available N, P, K but showed no relations with CEC and CaCO3. There were significantly positively correlations among soil alkaline phosphatase activity, urease activity and invertase activity. Soil catalase activity was significantly positively correlated with urease activity but showed no correlations with the other three enzymes.We draw the conclusions that compared to the artificial restoration, natural restoration is stronger in improving soil physical properties but worse in improving soil chemical properties; there have significant correlation between soil physicochemical properties and restoration years and plant coverage; mixed forest is greater in improving soil fertility than pure forest, particularly mixed forest of Robinia psendoacacia and amorpha fruticosa, but pure forest of robinia psendoacacia is better than pure forest of pinus tabulaeformis; restrict grazing can improve soil quality and control desertification effectively.
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