| Since the Industrial Revolution, the amount of nitrogen deposition has been increased annually. Increase in atmospheric nitrogen deposition may change the structure and function of the terrestrial ecosystems. In addition, nitrogen deposition can change the cycling of carbon, nitrogen, phosphorus and sulfur. Based on a six-year simulated N deposition experiment conducted in a typical grassland in Inner Mongolia Autonomous Region of northern China, we examined the effects of N additions on soil phosphorus and sulfur component and physiochemical properties of the test soils. There were nine N addition rates(0, 1, 2, 3, 5, 10, 15, 20 and 50 g N m-2 a-1), two frequencies of N addition(twice or 12 times annually), and two management modes(grass harvesting or not), and the treatments were classified as four modes. The research examined soil pH and soil electrical conductivity(EC), phosphorus component include total phosphorus, Al-P, Fe-P, O-P, Ca2-P, Ca8-P, Ca10-P, sulfur component include total sulfur, water soluble sulfur, adsorbed sulfur, insoluble sulfur. The main results and conclusions were as follows:(1) Soil pH significantly decreased under higher N addition rate, it decreased by1.1-1.9 units in treatments with N addition rate being 20 and 50 g N m-2a-1, respectively.Soil EC significantly increased with the increasing N addition rates. Within the experiment period, no significant change was observed for soil total phosphorus and total sulfur concentrations among N addition treatments. Soil Al-P, Fe-P and Ca2-P were significantly increased, but Ca8-P and Ca10-P concentrations were significantly decreased under higher N addition rates. With the higher rates of N addition, soil adsorbed sulfur and available sulfur concentrations increased significantly. Soil insoluble sulfur concentrations decreased with the increasing N addition rates.(2) The effects of N deposition frequency on soil total phosphorus, total sulfur and Ca10-P were not obvious. Under N addition of twice a year, the content of soil Al-P, Fe-P,O-P were higher than 12 times a year markedly; Soil water soluble sulfur was higher under once a month than twice a year; Under the low N addition treatment of fenced,Soil adsorbed sulfur was higher under once a month than twice a year, Under the higher N addition treatment of fenced, the result of adsorbed sulfur was opposite of low Naddition; Under the fenced treatment, the content of insoluble sulfur was higher under two times a year than once a month.(3) Under the treatment of fenced, soil Al-P, Fe-P, Ca8-P and O-P was significantly higher than mowing, soil adsorbed sulfur was also higher than mowing markedly, the content of insoluble sulfur was lower than mowing; The effects of fenced and mowing on soil total phosphorus, total sulfur, Ca2-P, Ca10-P and water soluble sulfur were not obvious.(4) Under the treatment of simulated nitrogen deposition, Soil phosphorus and sulfur component and other soil physicochemical properties have a close relationship.The content of soil Al-P, Fe-P, Ca2-P, adsorbed sulfur and available sulfur was negatively correlated with soil pH and soil EC, soil Ca10-P was positively correlated with soil pH. Soil Ca8-P, Ca10-P and insoluble sulfur was negatively correlated with soil EC. Soil Al-P, Fe-P, Ca2-P, O-P, Ca8-P was negatively correlated with CEC, and the Ca10-P was just the opposite. Soil Al-P, Fe-P and Ca2-P was positively correlated with soil micronutrient elements(Fe、Mn、Cu、Zn). Content of soil Ca8-P and Ca10-P was negatively correlated with Cu. Soil adsorbed sulfur and available sulfur were negatively correlated with soil Ca2+、Na+and CEC.The result obtained in this study will help us to understand the effect of atmospheric nitrogen deposition on soil nutrient migration and transformation of grassland ecosystems. It will be provide theoretical foundation for fertilizing management of grassland ecosystems in northern China. |
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