Effects Of Clear-felling On Soil Respiration In Sharptooth Oak (Quercus Aliena Var. Acuteserrata) Forest In Xiaolong Mountain

Soil CO₂efflux from forest soils is a key source of CO₂in the global carbon cycle,although forest ecosystem have been considered as potential C sinks. However, the role andthe importance of forests as C sources or sinks vary widely according to the forest type, treeage and forest management practices. Microclimate environment and forest soil C dynamicsin forest ecosystem was impacted intensively by clear-felling which was one of the majorforest management activities. Forest clear-felling also have the potential to impact autotrophicrespiration of root and heterotrophic respiration of microbial biomass. Thus, the change of soilCO₂efflux following clear-cutting has received considerable attention.Sharptooth oak forest and its clear-felling site were selected as study plots in XiaolongMountain. Soil respiration rate, soil temperature, soil water content, air temperature and airrelative humidity were measured from May2011to September2012in both plots. In addition,part of soil physical and chemical properties were also measured in both plots. Effects offorest clear-felling on temporal variation of soil respiration rate, carbon emission from forestsoil were studied. The correlativities between soil respiration rate and soil temperature, soilwater content, air temperature, air relative humidity, soil physical and chemical propertieswere analyzed by SPSS. The single factor models of soil respiration, which were fitted by soilrespiration rate and temperature or moisture, were constructed in both plots. The double factormodels of soil respiration rate were also constructed by soil respiration rate, temperature andmoisture in both sites. The results showed that:（1） Soil respiration rate showed significant diurnal variation in Sharptooth oak forest andits clear-felling plot, similar with the trend of5cm soil temperature diurnal variation, showedunimodal curve. The maximum values of soil respiration rate all appeared in15:00¹7:00.The mean soil respiration rate in clear-felling plot was lower than that in Sharptooth oakforest except Jun and July,2011.（2） Soil respiration rate showed obvious seasonal dynamics and appeared unimodalcurve in harptooth oak forest and its clear-felling plot, similar with air temperature and soiltemperature. The mean maximum and minimum values of soil respiration rate appeared inJuly and February, respectively. The mean maximum and minimum values were4.02，0.29μmolCO₂m^-2 s^-1in Sharptooth oak forest，and were4.62，0.13μmolCO₂m^-2 s^-1inclear-felling plot. During the whole determination period, the mean soil respiration rate in Sharptooth oak forest was greater than that in clear-felling site, but there was no significance（P>0.05）. The mean of monthly soil respiration rate in clear-felling plot was significantlygreater （P<0.01） than that in Sharptooth oak forest from the fourth month to sixth month afterforest clear-felling, and after then, the mean of monthly soil respiration rate in clear-fellingplot was significantly lower （P<0.05） than that in Sharptooth oak forest.（3） Annual carbon flux of soil respiration in clear-felling plot was lower than that inSharptooth oak forest, but there was no significance （P>0.05）. Annual carbon flux of soilrespiration was399.79⁴06.72g C m^-2 a^-1in clear-felling plot, and that in growing season,dormant season account for about85%,15%, respectively. Annual carbon flux of soilrespiration was approximately557g C m^-2 a^-1in Sharptooth oak forest, and that in growingseason, dormant season account for about83%,17%, respectively.（4） Correlation analysis of soil respiration rate and its influencing factors showed that,there was extremely significantly positive correlation relationships （P<0.001） between soilrespiration rate and air temperature, soil temperature. The correlation relationships betweensoil respiration rate and air temperature,5cm soil temperature in clear-felling plot wasstronger than that in Sharptooth oak forest, however, the correlation relationship between soilrespiration rate and10cm soil temperature clear-felling plot was weaker than that inSharptooth oak forest. The correlation coefficient between soil respiration rate and5cm soilwater content in clear-felling plot was greater than that in Sharptooth oak forest, but there wasa lower correlation coefficient between soil respiration rate and10cm soil water content inclear-felling than that in Sharptooth oak forest. There was significantly positive correlationrelationship （P<0.05） between soil respiration rate and total C at10cm depth in both plots.The correlation relationship between soil respiration rate and10cm soil total C in clear-fellingplot was weaker than Sharptooth oak forest. There were no significance （P>0.05） between soilrespiration rate and total N, C/N, total P, total K, pH in all soil depth in both plots.（5） During the whole determination period, there was significant exponentialrelationships between soil respiration rate and temperature （P<0.001）. Goodness of fit for soilrespiration exponential models in clear-felling plot was greater than that in Sharptooth oakforest. With the help of soil respiration exponential models,89.5%⁹2.3%of soil respirationrate variation could be explained by air temperature,5cm,10cm soil temperature inclear-felling plot, and79.8%⁸9.8%of soil respiration rate variation could be explained by airtemperature,5cm,10cm soil temperature in Shoarptooth oak forest.