Nitrate Distribution And Nitrification-Denitrification In The Soils Of Desert Areas,Northwest China

Nitrogen is the most valuable nutrition resources which plays an important role in the ecological environment and its circulation is the most important process that affect the globle warm in recently years. Identifying the distribution of nitrogen element and its different form is particularly necessary to understand its properties, on the other hand, studying the nitrification and denitrification process that controls the transform of the nitrogen element is quite important to understand its circulation. Shiyang River Basin and its adjacent Tengger Desert and Badan Jaran Desert, located in northwest China, is a typical fragile ecosystem area and is extremely sensitive to climate changes. Carrying out the research and investigation work on the distribution of nitrite and soil nitrification and denitrification process in this area is able to provide new sight for the global changes and ecosystem; meanwhile, it is also give important guidance for government to protect and improve the environment in this area.Using a combination of field investigation, theoretical analyses and BaPS analyses method, this paper studied the distribution of nitrite and chloride in different soil type and depth, soil nitrification and denitrification ratio as well as the breathing rate in different vegetation coverage and depth, and its influence factors in barren desert of Northwest China, the main results are followed:(1) The Cl-、NO3-profiles tend to be piston oscillations as a result of the severe evapotranspiration. Plant taking-up of moisture and nitrate preferentially makes the nitrate distribute differently in vadose zone. The presence of peaks in the nitrate profiles are probably proportional to the preferential taking-up of nitrate and due to be coincidence with the nutrient profile, which leads the concentration of nitrate to decline sharply with the soil depth. The peaks appeared near surface in NO3-with higher NO3-/Cl-molar ratios reflects active modern N-fixation by cyanobacteria. The higher NO3-/Cl-molar ratios are consistent with the bulge shaped Cl-, which dramatically indicates less vegetation present in the more drought environment to limit uptake of nitrate. The characteristics of chloride and nitrate tend to be distinct in different type of soil. The piston distribution of chloride and nitrate in the sand soil, which has a great conductivity and inferior water binding capacity, ttributes to the plant taking in the nitrate within its cycling in the soil along with intensive evapotranspiration, while the concentration of chloride and nitrate in the clay soil decreases with the moisture content.(2) The soil nitrification and denitrification ratio and the gross nitrification rates were tested using the BaPS analyses method. The gross nitrification rate is relatively low because of the arid climate and low coverage ratio of vegetation in our study area, However, the gross nitrification rate is quite different in different soil type and shows some varieties with the depth. The rates in the dark loessial soil is greater than that in the desert soil, and it becomes slow in the deep layer of the soil profile. Generally the denitrification ratio of the study area has very small values which is quite close to the detected limit of the BaPS because of the special environment of the low soil water content and good air capacity, that is not propitious to propitious to denitrification process.(3) We examined the relationship between the gross nitrification(denitrification) rates and different factors, such as the soil water content, temperature and the O-Slen P, and found that the rates was closely associated with soil water content, which shows a significant positive correlation. However, the relationship between the temperature and soil gross nitrification(denitrification) rates is not distinct in our study area. The soil concentration of O-Slen P also plaies a very important role to control the gross nitrification(denitrification) process, meanwhile we should Strengthen the research on its influence mechnism. Inetegrating the soil respiration and nitrification in the desert aeras, we found that soil nitrification was closely associated with soil respiration. A significant non-liner positive correlation existed between siol respiration and nitrification, soil nitrification increased with increasing soil respiration.