Studies On Quantity Dynamics Of Soil Microorganism And The Relation With Soil Nutrients Of Alpine Meadow In The Headwater Area Of Yellow River

Six different type of representative grasslands in the headwater area of yellow river were selected to investigate their soil properties including microorganism communities, soil nutrients, pH value and soil containing water in May (spring), August (summer) and November (late autumn). They are undegraded alpine meadow, medium degraded pasture, "Black- soil-patch" degraded meadow, 2 years-old artificial grassland, 4 years-old artificial grassland and 6 years-old artificial grassland. The quantity of soil microorganism, content of soil nutrients, pH value and soil moisture content, and their relationships were analyzed, which based on principles of soil microbiology and pedology. The main research results are as follows:1. The seasonal dynamics of soil microorganism With season changing the total soil microorganism presents the degressive tendency. Compare of the three seasons, there are the most microorganism in May, and the least microorganism in November. So did the tendency of bacteria. Actinomycete quantity decreases then increases regularly with change of season, and the minimum value appears in August. But the quantity of fungi increases as the season progresses, and it is lowest in May and highest in November.2. The distributing of soil microorganism in different type of grassland Compositive proportion of Soil microbial species of six grasslands have the difference slightly, but consistent on the whole. Among them, bacteria quantity is the most, actinomycete quantity is less and fungi quantity is the least. The proportions of them in total microorganism are 87%-99%, 1%-11% and 0.01%-0.3% respectively. For the different degeneration of natural meadow, the quantities of soil bacteria and actinomycete present the reducing tendency along with the degeneration of meadow, but the tendency of fungi quantity elevate with the degeneration aggravating of meadow. However, in artificial grassland, the quantities of bacteria and actinomycetes firstly decreased then increased. Campared with'black-soil-patch'degraded meadow, the quantities of bacteria and actinomycetes of 2 years-old artificial grassland were obviously higher, and the quantity of Fungi was lower, though it was higher when compared with undegraded meadow.3. The quantitive distribution of soil microorganism in soil section The vertical quantitive distribution of soil microorganism has a degressive tendency when the depth increased: the quantity of soil microorganism in 0-10cm soil layer is the most, less in 10-20cm soil lay, and the least in 20-30cm soil layer. In general, the quantity of soil microorganism in 0-10cm soil layer is 2-7 times more than in 10-20cm soil layer, and is 2-13 times more than in 20-30cm soil layer.4. The seasonal dynamics of soil nutrients The seasonal change of soil nutrients in six grasslands are different, also display multiplicity with changing of grassland type and soil nutrients. Soil organic matter in 2 years-old and 4 years-old grassland show a reversed'v'model, the rest of four grasslands all show a'v'model. Total phosphorus of six grasslands is highest in August and lower in May and November. The seasonal change of total nitrogen in native meadow has the same change with medial degenerative meadow,'black-soil-batch'degraded grassland and 2 years-old grassland. All of them had the most total nitrogen in August except for 4 years-old and 6 years-old grassland. Available N of soil in all samples ascend and then descend except for 6 years-old grassland. Available K of soil change with unimodal curve which firstly increases and then reduces and the peak value appears in august. Available K of other grasslands presents a'v'model. The soil of six grasslands is the neutral leaning alkali soil. The seasonal variation of soil pH value presents a'V'model only in 4 years-old grassland and displays a reversed'v'model in other grasslands, whose peak appears in August. Soil moisture content of six grasslands increases firstly then reduces with seasonal variation, finally reaches the maximum in August.5.The dynamic distribution of soil nutrients in different grasslands soil nutrients and moisture content of six grasslands differ in different month, but their distribution rule is basically consistent, that was to say, as the degree of degradation increased, soil nutrients presente the degressive tendency. Compared with "Black-soil-patch" degraded meadow, the soil nutrients and moisture content of 2 years-old grassland are higher, and 6 years-old grassland is lower than 2 years-old, however higher than 4 years-old. The soil nutrient and moisture content present reducing tendency as the depth of soil layer increases, namely the content of each index is the highest in 0-10cm soil layer and the lowest in 20-30cm soil layer. In terms of the potential hydrogen of soil, the pH value of native meadow is thelowest in each soil layers; the pH value of medial degenerative meadow is lower in surface layer and higher in middle-layer and under-layer than'Black-soil-patch'degraded meadow. The change of soil pH value is not obvious among artificial grasslands. The soil pH value of 4 years-old grassland is lower than 2 years-old and 6 years-old grassland in the August, but it higher than native meadow. For vertical distribution, soil nutrients present reducing tendency along with increasing of soil layer depth, namely they are highest in 0～10cm soil layer, and lower in 10～20cm soil layer, and lowest in 20～30cm soil layer. Soil acidity of six grasslands is lowest in surface layer, and increases along with the depth increases gradually.6. The relation between microorganism quantity and soil nutrients except pH value is negatively correlated with fungi quantity; other soil nutrients are positively correlated with bacteria quantity, actinomycete quantity and fungi quantity. Among them, bacteria quantity is extremely significantly positively correlated with organic matter, total N, total P, available N and available K, and it is significantly positively correlated with moisture content, and it is positively correlated with pH value, but the correlation is not significant. Actinomycete quantity is extremely significantly positively correlated with organic matter, total N, available N, available K and moisture content, and it is significantly positively correlated with pH value, and it is positively correlated with total P, but the correlation is not significant. Fungi quantity is extremely significantly positively correlated with organic matter, total N and available K, and it is significantly positively correlated with available N, and it is positively correlated with total P and soil moisture content, and it is negatively correlated with pH value, but the correlation are not significant. After the pathway analysis was done between soil factors and microbial factors, the conclusion was reached: available N, total P and available K is the most important factor affecting the bacteria quantity; the organic matter, total N, available N and available K are the most factors affecting actinomycete quantity; the total N and available K are the most factors affecting fungi quantity.