Study On Carbon Flux Of Three Types Of Typical Forests In Subtropical Zone

Subtropical forest eco-system plays an important role in mitigating the global climate change.However,relatively few researches about subtropical forest eco-system carbon flux variations and it's response to environmental factors conducted in this region.Moreover,most current forest ecosystem carbon flux studies were conducted only in a single ecosystem with it's response to environmental factors,and lack of soil respiration collaborative research in the mean time whitch limit insight research about characteristics of subtropical forest ecosystem carbon flux and it's control mechanism,especially under the background of global warming,comprehensive studying for multiple forest eco-system can help us better understand subtropical forest ecosystem carbon cycle mechanism,and it's role in the global carbon cycling.In addition,based on the three types of forest ecosystem carbon flux research,it's helpful for us to adjust the parameter of ecological process model,providing theoretical basis and foundation to accurately estimate subtropical forest ecosystem carbon budget.In this paper,carbon flux data and soil respiration data from moso bamboo(Phyllostchys edulis)forest in Anji county,lei bamboo(Phyllostachys violascens)forest in Taihuyan county and evergreen and deciduous broad-leaved mixed forest in Tianmu mountain were used to illustrate the variation charicters of carbon flux in the three types of forest ecosytems.Meanwhile,randomforest model was applied to fit carbon flux then importance score for environmental factors was also calculated in order to evaluate the importance of environmental factors.What's more,variation charicters of soil respiration in the three types of forest eco-systems were analiesd and the contributions of soil respiration to total forest carbon flux was also analized.Mainly results and concludions were as followed:(1)All the variation trends of carbon flux in the three types of forests like string “U”,in monthly diurnal variation scale,all the forests as carbon sink in day time,carbon source in night time.Moso bamboo forest as carbon sink in whole year,whereas for evergreen and deciduous broad-leaved mixed forest,in January and December,as carbon source,for lei bamboo forest,in December,as carbon source.The maximum carbon sequestration ratio in the three forest eco-system were 51.89%,25.213% and 56.284% for moso bamboo,lei bamboo and evergreen and deciduous broad-leaved mixed forest,respectively.Thare are statistic significant difference about monthly NEE and RE among the three forests,the maximum total NEE and GEE occurred in evergreen broad-leaved fores,whereas the maximum total RE occurred in lei bamboo forest.(2)Random forest model was used to fit the carbon flux in the three types of forests,results showed that both in training stage and testing stage,the model keeps high accuracy which illustrated random forest model was well fitted in simulation about carbon flux.The results of 10-fold cross-validation showed that random forest was stable when simulating carbon flux and internal parameter were reasonable,all the models about the three types of forests had good generalization ability and stability.(3)The importance score of environmental factors demonstrated that at monthly half hour scale,PAR was the control factor to carbon flux at all forests,and RH,VPD and T_S,SWC and T_S,T_A and T_S were the secondary impact factors for moso bamboo forest,lei bamboo forest and evergreen and deciduous broadleaved mixed forest,respectively.In monthly scale,all carbon flux at the three types of forests mainly affected by T_A and T_S,otherwise,VPD was also siginificantly affect the carbon flux at the three types of forests.(4)Soil respiration at the three types of forests all had obviously seasonal variation with unimodal variation trend.In June,soil respiration at moso bamboo forest reached the maximum value,then,evergreen and deciduous broad-leaved mixed forest(July)and lei bamboo forest(August).All soil respiration at the three types of forests controlled by soil temperature,no correlation was found between soil respiration and soil water contend at the three types of forests.Compared to unigram model,bigram modle had higher accuracy,to fit soil respiration at moso bamboo forest and evergreen and deciduous broad-leaved mixed forest Model9 was best fitted,whereas to lei bamboo forest Model10 was the best fiteed.The contibutions of soil respiration from high to low was 62.834%,61.951 and 43.498% for lei bamboo forest,evergreen and deciduous broad-leaved mixed forest and moso bamboo forest,respectively.