Effects Of Freezing And Thawing Alternation On Soil Nitrogen Pool In The Alpine Meadow

Qinghai-Tibet Plateau is considered one of the promoter regions of global change, which located in the eastern edge of Qinghai-Tibet Plateau alpine meadow area is also a research ecologist hot spots. A number of explorations were researched about the Qinghai-Tibet Plateau forest-ray changes, soil erosion and global climate change at home. But so far, relevant studies on freezing-thawing events which frequently occurred in Qinghai-Tibet Plateau have not been reported.There are different vegetation characteristics between the yin and yang slope in the Qinghai-Tibetan Plateau alpine meadow area, as well as without snow-covered in sunny area in the winter, which experienced frequent freezing and thawing alternation. In this paper, the soil from the Qinghai-Tibetan Plateau alpine meadow Songpan County, Kaka groove was investigated by freezing and thawing alternation simulation tests, performed in incubation laboratory, the content of soil microbial biomass C and N, content of each component of organic nitrogen, free amino acids, nitrate nitrogen, ammonium nitrogen and soluble organic matter in soil solution at different time (1 day,3 days,5 days,25 days,60 days) and different freeze-thaw temperature (4℃contrast,-4℃contrast,-4-4℃and-20-4℃)were analyzed so as to analyze the effects of freezing and thawing alternation on soil nitrogen pool of the Qinghai-Tibet Plateau. The results are as follows:1. With the freezing and thawing time changes, the trend of soil microbial carbon and nitrogen was firstly decreased and then increased. The content of soil microbial biomass carbon and nitrogen reached the minimum in the 1d freezing and thawing alternation. Among them, the decrease of microbial biomass C were 61.74%,30.47%,37.20% and 46.17%,while the decrease of microbial biomass N were 50.37% decrease,57.47%, 37.79% and 37.51% at each temperature treatments. Short-term freezing and thawing cycles had a significant influence on soil microbial biomass carbon and nitrogen (P<0.05),and the time of freezing and thawing alternation was the main reason for the content of microbial carbon and nitrogen.The ratio of MBC/MBN characterization of microorganism change in soil, MBC/MBN ratio first increased and then decreased, indicating that fungi/bacteria ratio have taken place corresponding change under freezing and thawing cycles.2. With the freezing and thawing time changes, the content of soil organic nitrogen was significantly different. Among them, amino acid nitrogen and amino sugar nitrogen varied with similar trend, firstly increased and then decreased, and reached the minimum after the 3d freezing and thawing alternation,while the trend of ammonia nitrogen was firstly increased and then decreased. The trends of unidentified hydrolizable nitrogen were different, and similar characteristics was firstly increased and then decreased.3. The content of soil soluble carbon and nitrogen was significantly different under the freezing and thawing alternation, and the content of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) varied the same trend, firstly increased and then decreased. Contents of DOC and DON reached the maximum after 1d freezing and thawing alternation.The ratio of DOC/DON characterization of dissolved organic matter content (DOM) in soil, DOC/DON ratio first increased and then decreased, indicating that the microbial biomass is the main source of DOM change in this study.4.Freezing and thawing alternation had a significant impact on soil nitrogen mineralization, in which the content of nitrate nitrogen changed with the freezing and thawing time,firstly increased and then showed decreased, and reached the maximum after 1d freezing and thawing alternation.Comparing to the based value, the content of them were came to 2.20,1.99,2.34 and 2.42 times; ammonia nitrogen and nitrate nitrogen varied with the same trend,which reached 1.78,2.42,3.45 and 4.24 times after 1d freezing and thawing alternation.5. With the freezing and thawing time changes, the content of Soil solution DOC, DON in soil solution was firstly increased and then showed a decreasing trend. The content of Soil solution DOC, DON increased significantly in the early freezing and thawing time, the content of soil solution DON under-4℃(CK2) temperature treatment was significantly higher than the other three temperature treatments at the same time. The study showed that freezing and thawing alternation had a significant influence on soil nitrogen pool in the alpine meadow. The study about effects of freezing and thawing alternation on soil nitrogen pool, which helping to explain the reasons for high mountain areas with lower soil nitrogen mineralization rates, so as to provide a theoretical basis for research on nitrogen cycle and ecological effects in alpine areas.