Effects Of Hydrothermal Control On Nitrogen Mineralization Of Five Forests In Southern Sichuan

Global warming is a serious challenge.Forest ecosystem plays an important role in global climate change,which means that it is important to understand the response regularity and sensitivity of soil nitrogen mineralization to temperature and humidity in different forest ecosystems.This also have positive effects on the estimation and prediction of soil mineralization rate in a certain region.In addition,it also provides an assistance to update artificial forest and solve issues of climate change.In order to understand the effects of temperature and humidity gradients on nitrogen mineralization on the surface soil layer of sassafras Sassafras,Mao Zhulin,Chinese fir forest and Metasequoia forest?0²0 cm?in the evergreen broad-leaved forest and artificial regeneration in southern Sichuan.The temperature gradient was 5,15,25 and 35,respectively,and the humidity gradient was 20%,40%and 60%,respectively.This study not only analyzed the relationship between temperature,humidity and soil nitrogen mineralization,but also examined and discussed the optimum temperature and humidity of nitrogen mineralization.Results were shown as follows:?1?The forest soil net ammonification rate,net nitrification rate,net nitrogen mineralization rate and temperature and humidity were extremely significant?P<0.01?,the interaction of temperature and humidity has a significant effect on soil net ammonification rate and net nitrogen mineralization rate?P<0.05?,however,besides Phyllostachys pubescens forest,no significant relationship was discovered between the interaction of temperature and humidity and net nitrification rate in other forest.?2?Under the same condition of moisture or temperature,the forest soil net ammonification rate,net nitrification rate and net nitrogen mineralization rate showed same pattern,that is,both of them increased with the rising of temperature?water content?,and reached peak at 25??60%FWC?,after that,these figures decreased with increasing temperature.In all of these 16 samples,the forest soil net ammonification rate,net nitrification rate and net nitrogen mineralization rate were the highest at 25?and60%FWC.The optimum soil water content of nitrogen mineralization in the soils of eucalyptus forest,bamboo forest,Chinese fir,M.edodes forest and natural forest were60%,58.8%,61.8%,65.5%and 57%FWC,respectively,and the optimum temperature was 25.5°C.25.9°C,26.5°C,25.6°C,and 25.6°C.The average inorganic nitrogen content and nitrogen mineralization rate of natural forest were higher than artificial pure forest.?3?By fitting a binary quadratic regression equation of the soil nitrogen mineralization rate?y₇?,soil moisture content?x₁?and temperature?x₂?in each stand,the maximum net nitrogen mineralization rate for each stand can be calculated.The heat combinations were:Qimu forest 60.6%FWC+25.6°C,Moso bamboo forest 57.4%FWC+25.8°C,Chinese fir forest 62.9%FWC+26.9°C,metasequoia forest 67%FWC+26°C,natural forest 57.4%FWC+25.8°C.?4?The Q₁₀0 values of soil nitrogen mineralization in different forest soils under different water content conditions decreased with the increase of temperature,and the Q₁₀values increased when the temperature increased from 5°C and reached at the highest value at 15°C,which suggests that the nitrogen mineralization of each forest is the most sensitive to the temperature in this range.