Soil Respiration And Its Affecting Factors In Pinus Sylvestris Var.mongolica Natural Forest In Da Xing'an Mountains

Soil is the largest carbon reservoir in terrestrial ecosystems,and soil respiration is an important process in which soil releases carbon dioxide into the atmosphere.Forests are an important part of terrestrial ecosystems and play a key role in maintaining global ecological balance.Studying the changing characteristics of forest soil respiration and its regulating mechanism is of great significance for reducing atmospheric CO₂ concentration and slowing the global greenhouse effect.In this paper,natural forests of Pinus sylvestris var.mongolica in different terrains(flat land,bottom,middle and top)in the Daxing'an Mountains forest area are studied.From June to October in 2018,LI-6400 was applied to natural forests of flat and sloping land in the Daxing'an Mountains forest area.The soil respiration and its components(heterotrophic respiration,autotrophic respiration,litter respiration,mineral soil respiration)dynamic characteristics were measured.The influencing factors were measured to study the relationship between soil respiration and influencing factors,in order to study the carbon cycle of forest ecosystem in the cold temperate zone of China.The results are as follows:(1)The monthly changes of soil respiration and its components in Pinus sylvestris var.mongolica natural forest in different terrains all showed a"single peak"curve,the total soil respiration,heterotrophic respiration,and mineral soil respiration of flat land were significantly higher than that of sloping land from June to August(P<0.01).The total soil respiration rate ranged from 1.00 to 8.78?mol·m^-2·s^-1,and the peak occurred in July or August;the ranges of heterotrophic respiration and mineral soil respiration were 0.49 to 7.86?mol·m^-2·s^-1and From 0.13 to6.74?mol·m^-2·s^-1,all of the peak values appeared in July;during the observation period,there were significant differences in the average values of total soil respiration,heterotrophic respiration,and mineral soil respiration.The average value of total soil respiration,heterotrophic respiration,and mineral soil respiration in flat land were significantly higher than that of down and middle slopes(P<0.05),but there were no significant differences between that of flat and up slopes;the range of autotrophic respiration was 0.35?3.21?mol·m^-2·s^-1,and the peak value appeared in August,it was significantly higher in the slope land than flat land(P<0.05),the difference between different slope positions was not significant;litter respiration was 0.19?2.22?mol·m^-2·s^-1 Fluctuations and differences between regions did not reach significant levels.(2)The soil respiration and heterotrophic respiration of Pinus sylvestris var.mongolica natural forest in different terrains have extremely significant exponential correlations with the soil 10 cm temperature(T₁₀)(P<0.01).The autotrophic respirations in the flat,bottom and middle are significantly correlated with soil temperature.Soil temperature can explain 69.3%?83.8%,68.77%?88.7%,and 39.7%?76.2%of the monthly changes for total soil respiration,heterotrophic respiration,and autotrophic respiration of Pinus sylvestris var.Therefore,soil temperature was the key factor affecting soil respiration in Pinus sylvestris var.(3)In the middle and top,there was a significant linear positive correlation between soil moisture and total soil respiration(P<0.05);but in the bottom and middle,there was a significant linear correlation between heterotrophic respiration and soil humidity(P<0.05);There was a significant linear correlation between autotrophic respiration and soil moisture in different terrains(P<0.01);soil moisture can explain 6.4%?41.5%,0.9%?44.4%,and 59.3%?78.9%of the monthly changes for total soil respiration,heterotrophic respiration,and autotrophic respiration Pinus sylvestris var.(4)The total soil respiration of Pinus sylvestris var.Mongolica forest in different terrains has a significantly significant positive correlation with the total organic carbon of 0-10 cm(P<0.01).in some terrains,total nitrogen,easily oxidizable organic carbon,hydrolyzed nitrogen,carbon-nitrogen ratio,and p H have extremely significant exponential correlations with total soil respiration(P<0.01).(5)There were a significant or extremely significant correlations between the total soil respiration and various soil enzymes.The total soil respiration on the flat and middle had a significant or very significant positive correlation with the soil catalase,urease,cellulase,invertase,and protease;The soil total respiration on the bottom had a significant positive correlation with the invertase and cellulase,and had a significant negative correlation with catalase;The soil total respiration on the top had a very significant positive correlation with the catalase,and had a significant negative correlation with protease.