Carbon Balance Of Pinus Tabulaeformis Forests And Quercus Aliena Var.acuteserrata Forests At Huoditang Forest Region In The Qinling Mountains

With the intensification of global warming,more and more attention has been paid to the study of carbon cycle and carbon balance in forest ecosystems.The uncertainty of forest carbon balance is mainly caused by the accurate estimation of vegetation carbon sequestration capacity and its exchange flux with atmosphere.In recent years,under the influence of extreme weather and insect pests,the main tree species—Pinus tabulaeformis and Quercus aliena var.acuteserrata of Huoditang forest have formed a large number of logs,which has an impact on the carbon balance of the ecosystem in the region.In this study,the data of trees,shrubs and herbaceous resources of P.tabulaeformis forest and Q.aliena var.acuteserrata forest in Huoditang were investigated,while the carbon density and carbon increment of vegetation of the two forest types were estimated by combining biomass model and carbon content of different vegetation.The monthly and diurnal dynamics of soil respiration and log respiration in two forest types were measured and analyzed,and the influencing factors were explored,and the annual fluxes of soil respiration and log respiration were calculated.The carbon sink increment and carbon budget characteristics of P.tabulaeformis forest and Q.aliena var.acuteserrata forest in this area were calculated and evaluated.The aim is to provide data support and theoretical guidance for the evaluation of forest ecosystem service function and carbon sink in the Qinling Mountains,and to provide a new idea for the accurate estimation of regional forest ecosystem carbon balance.The main results are as follows:（1）The carbon content rate of different tree species is obviously different,the relationship of carbon content rate of each organ of P.tabulaeformis is leaf>branch>stem>skin>root,and the carbon content rate of each organ of Q.aliena var.acuteserrata is root>skin>branch>stem>leaf.In one year,the carbon density of trees in both stands increased.The carbon increment per unit area of trees in P.tabulaeformis forest was 10.45 t·hm^-2·a^-1,and8.57 t·hm^-2·a^-1 in Q.aliena var.acuteserrata forest.The ratio of vegetation biomass and carbon density in the shrub layer of the two forest communities was very small,about 2%of the total forest land.In the case of P.tabulaeform forest,the biomass of shrubs and herbs increased by1.69 t·hm^-2·a^-1,and the carbon stock increased by 0.76 t·hm^-2·a^-1.For Q.aliena var.acuteserrata forest,the biomass of shrubs increased by 0.82 t·hm^-2·a^-1,and the biomass of herbs decreased by 0.29 t·hm^-2·a^-1,and the carbon stock increased by 0.24 t·hm^-2·a^-1.The overall carbon stock of P.tabulaeformis community increased by 11.21 t·hm^-2.The overall carbon stock of Q.aliena var.acuteserrata community increased by 8.81 t·hm^-2.P.tabulaeformis forest has stronger carbon sequestration capacity than Q.aliena var.acuteserrata forest.（2）The daily and monthly variations of soil respiration in P.tabulaeformis and Q.aliena var.acuteserrata forests both showed obvious single-peaked curves.During the growing season,the maximum value of soil respiration in P.tabulaeformis forest was between13pm to 15pm,while the daily peak value of soil respiration in Q.aliena var.acuteserrata forest was around 15pm.The maximum value of soil respiration in P.tabulaeformis forest occurred in July with an intensity of 5.65±0.14μmol·m^-2·s^-1 and the minimum value occurred in January with an intensity of 0.33±0.02μmol·m^-2·s^-1.The total amount of CO₂ released in a year was 33.85 t·hm^-2·a^-1.Soil respiration in Q.aliena var.acuteserrata forest reached its peak in August was 5.92±0.27μmol·m^-2·s^-1,and the minimum also occurred in January with a respiration rate of 0.28±0.03μmol·m^-2·s^-1 and a total annual CO₂ release of 31.38 t·hm^-2·a^-1.（3）Soil temperature was the environmental factor with the greatest influence on soil respiration,and there was a highly significant positive correlation between soil respiration and soil temperature（p<0.05）in both P.tabulaeformis and Q.aliena var.acuteserrata forests.The correlation coefficient between soil respiration rate and soil temperature was 0.52704 for P.tabulaeformis forest and 0.48761 for Q.aliena var.acuteserrata forest.The effect of soil moisture content on soil respiration was not significant in this study,and moisture was not the main limiting factor for soil respiration in this area.Soil respiration rate had a significant negative correlation with soil bulk density（p<0.05）and a highly significant positive correlation with soil porosity（p<0.01）.It was positively correlated with soil sand content and negatively correlated with soil clay content（p<0.05）.Among the soil chemical properties,soil organic matter content and soil respiration rate showed a significant positive correlation（p<0.05）.（4）The peak of respiration rate of P.tabulaeformis log in a day was between 13:00 and15:00,and the daily and monthly changes among the five decay classes showed:III>IV>V>II>I.The maximum value of respiration rate of Q.aliena var.acuteserrata log in a day was around 15:00,and the daily and monthly changes among the five decay classes showed:Ⅳ>Ⅲ>Ⅱ>Ⅴ>Ⅰ.The respiration of log of the five decay classes of the two species reached its peak in July to August and the lowest value occurred in February.The total annual CO₂ release from log of P.tabulaeformis was 2.48 t·hm^-2·a^-1,and that of Q.aliena var.acuteserrata was2.55 t·hm^-2·a^-1.There was a significant positive correlation between log respiration rate and log temperature（p<0.05）,and log temperature could explain more than 73%of the log respiration pattern.The Q₁₀ of log respiration ranged from 2.83 to 4.20 for P.tabulaeformis and from 1.64 to 5.25 for Q.aliena var.acuteserrata.There was a significant positive correlation between log respiration rate and log moisture content（p<0.05）.There were significant differences between the water content of log of P.tabulaeformis and Q.aliena var.acuteserrata in different decay levels（p<0.05）,and the water content of log showed an increasing pattern with the deepening of decay.（5）The CO₂ release from log respiration of P.tabulaeformis forest in Huoditang accounted for 7%of the total heterotrophic respiration.The log respiration of Q.aliena var.acuteserrata forest accounted for 8%.The annual net CO₂ uptake of P.tabulaeformis forest in Huoditang was 4.80 t·hm^-2·a^-1,which showed the carbon sink.The annual net CO₂ uptake of Q.aliena var.acuteserrata forest was-1.65 t·hm^-2·a^-1,which showed as a carbon source,but if log respiration was not considered,the annual net CO₂ uptake of Q.aliena var.acuteserrata forest was 0.90 t·hm^-2·a^-1,which showed as a weak carbon sink.