| The influence of simulated nitrogen deposition on soil respiration was studied in Larix principis-rupprechtii Plantation in Taiyue Mountain.Through the field observation,to manually add different nitrogen concentration gradient by setting the sample area.Simulated nitrogen deposition experiment was carried out.There are four control groups of simulated nitrogen deposition process,blank group 0 kg N·hm-2·a-1,LN:50 kg N·hm-2·a-1,MN:100 kg N·hm-2·a-1,and HN:150 kg N·hm-2·a-1.Simulated nitrogen deposition time for the end of April to the end of September 2016,a total of six times;determination of breathing time in the middle of May to the end of October,choose a month two days the weather is sunny,interval during the 15 days,using LI-8100 soil carbon flux measurement system,5 cm of soil respiration and soil temperature and humidity are measured.To study the differences of soil respiration components of Larix principis-rupprechtii by adding different nitrogen concentrations and impact mechanism of each composition,for the deep understanding of nitrogen deposition under the background of Shanxi province of Larix principis-rupprechtii plantation ecosystem carbon flux change is of great significance.The results showed:(1)Soil respiration,microorganism respiration and root respiration all had significant seasonal variation under simulated nitrogen in the growing season.Simulated nitrogen deposition does not change the growing season characteristics of soil respiration components.The rates of total soil respiration in CK is 3.70±0.26pmol·m-2·s-1,LN is 4.3610.50?mol·m-2·s-1,MN is 4.90±0.66?mol·m-2·s-1,HN is 5.99±0.82?mol·m-2·s-1.Three groups of nitrogen added under the soil respiration rate were higher than blank control group,and group of high nitrogen concentration and soil respiration rate was significantly higher than control(P<0.05),high nitrogen concentration significantly contributed to the soil respiration rate.Simulated nitrogen deposition contributes to the soil respiration rate,and it changes greatly under high nitrogen concentration(P<0.05).High nitrogen concentration promotes the total soil respiration in a large degree.The rates of microorganism respiration in CK is 3.25±0.24?mol·m-2·s-1,LN is 3.86±0.43?mol·m-2·s-1,MN is 4.40±0.60?mol·m-2·s-1 and HN is 5.20±0.72?mol·m-2·s-1.Agree with soil total respiratory rate,nitrogen added three group were increased soil microbial respiration rate simulated nitrogen deposition contributes to the microorganism respiration,and it changes greatly under high nitrogen concentration(P<0.05).The rates of root respiration in CK is 0.46±0.06p?mol·m-2·s-1,LN is 0.50±0.10?mol·m-2·s-1,MN is 0.51±0.12?mol·m-2·s-1 and HN is 0.79±0.15?mol·m-2·s-1.Simulated nitrogen deposition contributes to the root respiration,but it changes slightly under high nitrogen concentration(P>0.05).(2)During the whole growing season of 2016,the temperature of soil in 5 cm increases first and then drops under four nitrogen concentrations,it also has obvious seasonal change characteristics.The temperatures under the four nitrogen concentrations all reach their climax.The highest temperatures of soil in the CK,LN,MN,HN group are 16.6?,16.7?,15.8? and 16.8?.The lowest temperatures of soil are in May,they are 6.6?,7.5?,7.0 ? and 7.5?.The temperatures have slight changes with the increasing of nitrogen concentrations.Thus simulated nitrogen deposition has no effect on the temperature of soil and the seasonal change characteristics of soil temperature.(3)During the whole growing season of 2016,the rates of plantation soil respiration,microorganism respiration and root system respiration under the four nitrogen concentrations all raise with the increasing of temperature of soil in 5 cm.,the rate of root system respiration does not have close relationship with the temperature of soil,(P>0.05),while the rates of plantation soil respiration,microorganism respiration have close relationship(P<0.05).What's more,the microorganism respiration has the closest relationship with soil temperature(P<0.01).Soil respiration rate,microbial respiration rate and root respiration rate and soil 5 cm temperature and humidity between double factor model fitting R2 values are higher than total respiratory rate,soil microbial respiration rate and root respiration rate and soil 5 cm temperature or humidity single factor model fitting R2 value,suggesting that oil 5 cm temperature and soil 5 cm moisture on soil respiration rate higher than that of single factor explains quantity variation explanation.This shows that soil temperature and water content can better explain the change of soil respiration.(4)During the whole growing season of 2016,the rates of soil respiration and microorganism respiration under the four nitrogen concentrations are higher than them in the growing season of 2015.Under the four nitrogen concentrations,the amount of soil respiration rate increase are 8.8%,51.4%,18.9%and 17%.The amount of microorganism respiration rate increase are 15.7%,81.2%,33.0%and 23.9%.While root system respiration rate is lower then that of 2015.Under the four nitrogen concentrations,the amount of root system respiration rate increase are-42.2%,-33.3%,-37.8%and 12.9%. |
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