Effect Of Different Land Utilization On Soil Nutrients And Grassland Vegetation In Alpine Meadow

The fenced (5 years) grassland, lightly degraded and human-induced restoration grassland, medium degraded grassland, heavily degraded "black soil patch"grassland, sandy grassland and oat artificial grassland in alpine grassland of Maqu were selected as research objects, their characteristics of nutrition contents and vegetation were studied in this research. The results were shown as follows:Compared to fenced and restoration, the contents of soil organic carbon (SOC), total N, available N, total P and available P under degraded grassland and oat filed sharply declined, whereas pH increased greatly. The change of total K and available K contents were unconspicuous, however, the content of organic carbon, inorganic nitrogen (NH4+-N+NO3-N) and ammonium nitrogen were all the highest in lightly degraded and human-induced restoration grassland soil, the values were 8.78g/kg, 49.44mg/kg,and 42.71mg/kg, respectively. However, the content of nitrate nitrogen was the highest in heavily degraded "black soil patch" grassland and reached 13.21mg/kg. Correlation analysis showed that correlations existed among nutrients, there were significantly positive correlation among SOC and total N, available N, total P, available P, total K, available K, respectively; while soil pH was significantly negatively correlated to other nutrients. Both total nitrogen and ammonium nitrogen had significant positive linear correlation with organic carbon (P＜0.01). The total nitrogen and inorganic nitrogen content in soil was positively related to organic matter (P<0.01), suggesting that the decrease of organic matter due to reclamation and degradation might be the main cause of the nitrogen content decrease in soils.Appropriate evaluation of phosphorus (P) fractionation in soil is a prerequisite for ensuring the productivity and long-term sustainable management of alpine meadow systems. The P fractionation method based on the Hedley's P fraction schedule which modified by Tiessen and Sui were used to study the soil P fractionation under different grassland ultilization. In general, the various P fractions account for percentage of TP at the six plots could be quantitatively ranked in the following order:Residual-P>Dil.HCl-Pi>NaOH-Po>Conc.HCl-Po>Conc.HCl-Pi> NaHCO3-Po>NaHCO3-Pi>H2O>Na-OH-Pi. The concentrations of all Pi fractions varied significantly under different use alpine meadow soils. The correlation analysis showed a significantly positive relationship between labile P and SOC, Residual-P, however, significantly negative relationship was found between labile P and pH. These results indicated that the alpine meadow soil P fractions were significantly affected by different grassland use.The features of grass functional group, species diversity and biomass under different land utilization were slso studied in this research. The results showed that:(1) Grassland functional group sharply varied under different land utilization patterns. The forbs played a pivotal role in grazing grasslands, as a single superior species grasses excelled other functional group in sandy and fenced land, while poisonous grasses were black beach's dominate functional group; (2) The high grass species richness and diversity were maintained by grazing, whereas maximum community productivity occurred at fenced land though it had the least species and the lowest diversity; (3) A significant linear negative correlation was found between the community biomass and species diversity, which means community biomass was elevated with the diversity index decreased.