The Influence Of Heavy Fire Disturbance On The Soil Nutrient Changes In The Larix Gmelinii Forest

Forest ecological system of soil nitrogen mineralization is one of the most important function of ecosystem. Nitrogen mineralization rate determines the availability of nitrogen (which was used for plant growth) in the soil. Research on the effect of soil moisture, physical and chemical properties, soil microorganisms, and other natural or man-made interference and many other factors is an important approach to reveal the regulation mechanism of nitrogen mineralization. Fire is an important natural interference factors for the forest ecosystems in north China, and the mechanism of soil nitrogen mineralization in response to fire disturbance is poorly understood. Through field sampling and lab analysis, we studied the dynamic variations and correlations between the effect factor of nitrogen mineralization rate in the soil in the Daxinganling Mountain of China. The main results are summarized as follows:1. The effect of soil nitrogen mineralization in response to fire disturbance:The ammonium nitrogen content, the Nanwenghe and Tahe soil show the same change trend, after fire disturbance, it overall showed a significant increase of ammonium nitrogen content, increased about 4 mg/kg. And the content of ammonium nitrogenat of Mohe had no obvious change. For the change of the content of soil effective phosphorus and available potassium showed obvious regional differences. this experiment found that the soil moisture content and soil PH value were not the same in response to fire disturbance in the different part of Daxinganling Mountain of China. The soil moisture content and soil PH value of Nanwenghe and Tahe were not obvious changed after fire disturbance, which shown no significant difference (P> 0.05), while the soil moisture content and soil PH value of Mohe showed significant differences. After fire disturbance, the soil moisture content of Mohe were shown obvious increase trend, while the soil PH value change fell significantly in Mohe. The effective phosphorus content in Nanwenghe showed a significantly decreased after fire disturbance, while in Tahe the effective phosphorus content showed an opposite trend. The effective phosphorus content in Tahe did not changed significantly. The rapidly available K content in Nanwenghe shown that there was no significant difference after fire disturbance, but the rapidly available K content in Tahe had increased significantly. While in Mohe the content had declined. This experiment also found total organic carbon (TOC) showed significant differences between topsoil and subsoil. In the topsoil, the total organic carbon (TOC) content of Nanwenghe and Tahe was increased, and the TOC content in Mohe were reduced. In contrast, in the subsoil, the fire interference did not effet the TOC content in the Daxinganling Mountain of China. While the microbial biomass carbon (MBC) content shown some differences.2. The correlation between the influence factor of soil nitrogen mineralization:correlation analysis found that the soil moisture content and other soil nitrogen mineralization influence factor had interaction with each other. In the topsoil, the soil moisture content had a significant negative correlation with soil available phosphorus content and soil PH value, meanwhile in the subsoil, the soil moisture content had significant negative correlation with rapidly available K content, ammonium nitrogen and soil PH value. The content of soil carbon determination for our understanding of the mechanism of soil nitrogen mineralization is indispensable. This study found that, there were significant positive correlation between MBC and TOC no matter the topsoil or the sobsoil (P< 0.01). Further study found that in the topsoil, MBC and TOC had certain influence with ammonium nitrogen and rapidly available K. In the subsoil, there were significantly negative correlation between MBC and TOC and effective phosphorus content (P < 0.01), therefore, the MBC and TOC which were interaction with different nutrients in the soil. Overall, these factors interact with eath other to affect the nitrogen mineralization rate, and ammonium nitrogen is mainly affected by the soil physical and chemical properties.