Response To The Nitrogen Deposition From Carbon Dynamics Of The Burned Larch Forest Area In Greater Khingan Mountains

Nitrogen deposition is the process by which the active nitrogen compounds in the atmosphere fall to the surface through rainfall(wet precipitation),dust(dry precipitation)and other means,when nitrogen deposition acts on forest ecosystem,it will affect the structure and function of forest ecosystem directly or indirectly.Being regarded as the most common disturbances in the in terrestrial ecosystems,fire is also an important factor for the regeneration of the Larix gmelinii in the Great Khingan area.The Great Khingan area is the main area of forest distribution in north China and the area with the highest frequency of forest fires.Based on the above reason,we would explore the response to the growth rate of larch biomass,the fine root biomass,the soil respiration and microbial community structure to nitrogen deposition.This simulated atmospheric nitrogen deposition investigate the response of plant biomass growth to nitrogen addition in Larix gmelinii forests(from 2014 to 2016).Four nitrogen(NH4NO3)addition levels were conducted as control(CK,0 g·m-2·a-1),low Nitrogen treatment(TL,2.5 g·m-2·a-1),middle Nitrogen treatment(TM,5 g·m-2·a-1),high Nitrogen treatment(TH,7.5g·m-2·a-1).The NH4N03 was applied with 32 L distilled water and was sprayed evenly on the sample plot with back atomize monthly during annual growth season(May-October).Same amount of distilled water without N was applied in the control sample)The research results were shown as follows:1)The rate of biomass growth under nitrogen treatment was significantly higher than the control group during the experiment periods(p<0.05).The rate of biomass growth was significantly different(p<0.05)among different treatments.The growth rate in 2016 was significantly higher than that in 2014 and 2015(p<0.05);There was no significant difference among the different treatments in 2014(p<0.05);In 2015,the rate of growth under TL was significantly higher than that under TM and TH(p<0.05);in 2016,the rate of growth under TL was significantly higher than that under TH(p<0.05),different treatments had different effects on different diameter class as well.The growth rate of the Larix gmelinii biomass(p<0.05)between 10?15 cm diameter class was significantly increased with TL treatment in the year of 2014 and 2016:the growth rate of the Larix gmelinii biomass(p<0.05)that between 10?15 cm diameter class and 15?20 cm diameter class was significantly increased with TM treatment in all experimental years;the growth rate of the all three diameter class of Larix gmelinii biomass(p<0.05)that above 10 diameter class was significantly increased with TH treatment in all experimental years.2)The rate of soil respiration showed a typical seasonal variation,and the seasonal pattern of respiration is similar to the soil temperature at 5 cm soil depth.There were differences in the monthly peak of soil respiration rate,however,the peak values of the control and the high Nitrogen treatment were found in August while the peak values of the low Nitrogen treatment and middle Nitrogen treatment processing were found in in July.According to the model,the soil carbon emission in control,low nitrogen treatment,middle Nitrogen treatment and high Nitrogen treatment is 380,455,429 and 370 g-m-2,respectively.The fine root biomass has a fairly strong seasonal appearance and each treatment reaches its peak in August;the carbon storage of fine roots under low nitrogen treatment was significantly higher than the others(p<0.05);the Carbon storage of fine roots under middle nitrogen treatment was significantly higher than that under high Nitrogen treatments and control group.There is not significantly difference for fine root carbon storage between high nitrogen treatments and control group.The carbon storage of fine roots under low nitrogen,middle Nitrogen and high Nitrogen treatment were 40%,24%and-13%higher than the control group,respectively.3)The diversity and abundance of bacteria and fungi showed a significant decrease under TH treatment in spring and autumn.TL and TM treatment significantly increased the diversity and abundance of bacteria and fungi in the spring and increased the abundance of fungi in the autumn.The physical and chemical properties of soil can directly affect the microbial community structure.In this study,we also found some taxa that have obvious responses to nitrogen deposition or seasonal change,which can be used as indicators of nitrogen addition and seasonal change response in the future.