Diurnal changes of soil respiration of mid-subtropical forest and its relationship with soil temperature and humidity

Forest soil respiration is an important part of soil respiration of the terrestrial ecosystems and the dynamic changes of forest soil respiration,which has great impact on the global carbon balance.Currently,the research of soil respiration of mid-subtropical forest is relatively weak.Taken the Jinggang Mountain National Nature Reserve as the study area,this paper monitored the soil respiration of main mid-subtropical forest types during the growing season using an infrared gas exchange analyzer(Li-8100),and analyzed its relationship with soil temperature and humidity.The results showed that: ①soil respiration of each forest type was high and active during the day,but low and inactive in the night.The most active period of soil respiration occurred between 10:00 to 14:00.The intensity curve of daily soil respiration followed the inverted U-shaped.②The soil respiration of the broad-leaved forests(dominant plant species: Castanopsis eyrei(Champ.)Tutch),coniferous forests(dominant species: Pinus taiwanensis),mixed forests(dominant plant species: Schima argentea Pritz. Cunninghamia lanceolata(Lamb.) Hook) and bamboo forests(dominant plant species: Phyllostachys heterocycla cv.Pubescens) varied from 2.1~5.3、2.19~4.02、1.27~4.23 and 1.8~6.35 μmol·m-2·s-1,respectively.The average soil respiration of the mixed forests was smaller than other kinds of forests,while its soil temperature was lower.Compared with the soil temperature humidity of the broad-leaved forests and bamboo forests,the average soil respiration was higher.Also,the average soil respiration had a big floating range,and mainly affected by environmental factors.③Analysis of soil respiration data of the four forest types using Excel and Sigmaplot statistical software,results showed that the soil respiration of broad-leaved forest did not correlate significantly with soil temperature;When the soil volumetric moisture content of coniferous forest was 25.02%,the soil respiration rate had a point of demarcation;there is an inverted U relationship between mixed forest soil respiration and temperature,and its respiration decreasesd as the soil volumetric moisture content increased;the relationship between bamboo forest soil respiration rate and the soil volumetric moisture content was similar with the mixed forest.In a word,probably due to the smiller soil porosity caused by heavier rainfull,the soil respiration activity was affected,thereby the correlation between soil respiration and soil temperature,humidity was not obvious among all forest types.