The Response Of The Soil Organic Matter Content To Nitrogen Addition And The Plant Functional Groups Removed In Degraded Grasslands

In this study we selected lightly degraded and heavily degraded typical grassland communities in Baiyinxile rangeland of Xilinguole steppe, setting nitrogen addition test (respectively adding NH4NO3 0g/m2, 30g/m2, 50g/m2,80g/m2), and functional groups removed test (The plants were classified according to the energy functional groups; namely high energy plant functional groups, middle energy plant functional groups, low energy plant functional groups; the other two function groups were cut off to retain a single group in each treatment group) to research the response of the different layered (0-10cm, 10-20cm, 20-30cm) soil organic matter content to the nitrogen adding gradient and the energy plant functional groups removed under different degraded condition.The main results as follows:(1) Compared the two different degradation degree of grassland, 0-20cm layer of soil organic matter in lightly degraded grassland is significantly higher than the heavily degraded grassland, there is not significant difference in 20-30cm layer of soil organic matter content between the two types of grassland. Adding nitrogen did not significantly change this pattern.(2) The response of the different degree of degraded grassland to nitrogen addition is different.For lightly degraded grassland, the response of nitrogen addition on soil organic matter is mainly concentrated in the 0-20cm layer, at 30g/m2 nitrogen addition, soil organic matter was significantly increased, nitrogen addition significantly increased soil organic matter content, which meant that nitrogen is the major limiting factor in lightly degraded grassland; For heavily degraded grassland, Adding nitrogen gradient did not change soil organic matter content significantly, which meant that nitrogen is not the main limiting factor in heavily degraded grassland.(3) With the soil depth and degree of degradation increased, the soil organic matter significantly decreased in grassland; Plant functional groups removed were significantly increased soil organic matter content.the main effect factors of soil organic matter content, the role of the order: soil depth> degradation degree> functional groups removal(4) Plant functional groups removed were significantly increased soil organic matter content in two different degraded grassland. For lightly degraded grassland, retaining a single high energy plant functional groups and low energy plant functional groups can significantly affect organic matter,but there is no significant difference among the three different plant energy functional group removed; For heavily degraded grassland, retaining a single high energy plant functional groups can significantly affect organic matter, there is no significant difference among the three different plant energy functional group removed, except 20-30cm layer of soil organic matter content is significant effect between high energy plant functional groups and low energy plant functional groups.