The Response Of Stipa Grandis And Cleistogenes Squarros Root System To Nitrogen Adding Gradient In Degraded Grasslands

Ecosystem function of north China grassland degenerate seriously for long-term exploitation, utilization. Ecological system development direction from the structural damage to the functional disorder. Stipa grandis is constructive species of typical grassland. Cleistogenes squarrosa is dominant species in deteriorated grassland. The objective of this study is to understand the response of Stipa grandis and Cleistogenes squarrosa root system variation tendency to nitrogen adding gradient and uncontested grassland. In Xilinguole League, light degraded and heavy degraded typical grassland be selected of Baiyinxile pasture, do4nitrogen adding gradient (0>30,50,80g NH4NO3/m2). The objective of this study is to understand the response of Stipa grandis and Cleistogenes squarrosa root system to nitrogen adding gradient by Delta-T SCAN root analysis system, measure root area, diameter, volume, length and aboveground height, root depth.The main results as follows:(1) Results show that some version:under competition with the increase of nitrogen adding gradient, the root length and surface area, volume of Stipa grandis signally increase in heavily degraded grassland, and there is a outstanding positive correlation between the root length, surface area and volume. With the increase of nitrogen adding gradient, the root depth and above-grand height signally increases in heavily degraded grassland, and there is a significantly positive correlation between the root depth and above-grand. While with the increase of nitrogen adding gradient, the response is not significant in lightly degraded grassland. Root diameter in heavily degraded grassland is significantly lower than that in light degraded grassland under no nitrogen added conditions. Root length, area, volume, above-ground height and root depth in heavily degraded grassland is significantly higher than that in light degraded grassland under high nitrogen(80g/m2) conditions. With the increase of nitrogen in soil, the root system of Stipa grandis uptake enough nutrition for its development by increasing root length to expand root system room. Nitrogen of soil always the key factor that influences in degraded grassland, and the relationship between root system became closer with the degradation degree of grassland.(2) Under competition with the increase of nitrogen adding rates, the volume and diameter of root at50g/m2nitrogen adding rates were significantly higher than the other three treatments, it is indicated that moderate soil N addition is beneficial to enlarge root-diameter of the dominant species Cleistogenes squarrosa in degraded grassland, but not to root elongation, and there was threshold of nitrogen adding rates influencing the root system of Cleistogenes squarrosa. There were not significantly linear correlations between length, diameter, surface area, volume of root and nitrogen adding rates.(3) Compare the root system under the contested and uncontested, the response of Stipa grandis is not significant to the nitrogen adding gradient without the competition, root miniaturization of Stipa grandis under the competitive pressure from Cleistogenes squarrosa. the root of Stipa grandis is wider to the nitrogen adding gradient without the competition, and root miniaturization of Cleistogenes squarrosa under the competitive pressure from Stipa grandis.