Study On The Characteristics Of CO₂ Exchange At Leaf And Canopy Leaves Of Typical Plants In An Evergreen And Deciduous Broad-leaved Mixed Forest In Tianmu Mountain

CO₂ fluxes and three dominant plants of an evergreen and deciduous broad-leaved mixed forest in Tianmu Mountain forest ecosystem from October in 2014 to September in 2015 in Zhejiang province,were respectly measured by the eddy covariance micrometeorological method and the eco-physiological method,to explore the CO₂ and Photosynthetic characteristic parameters dynamic variations at daily,monthly,seasonal and annual scales as well as relationship with environmental factors,the results showed that:?1?Annual average photosynthetic active radiation?PAR?was 194.61 ?mol·m-2·s-1.The PAR generally showed a double peak curve in this year.The lowest average was in December,only 84.26?mol·m-2·s-1,and the highest was in August,which was 283.65?mol·m-2·s-1.Annual air temperature?Ta?showed an obvious single peak curve,and the annual average Ta was 11.05 ?.In December,the average Ta was the lowest,only 0.05 ?,and the highest was in August,which reached 20.45 ?.Annual average relative humidity?RH?was about 71.33%,the lowest was in December,only 45.69%,and the highest was in July,reaching 87.74%.Affected by RH and Ta,the VPD regularity was poor.Annual average VPD was 0.39 kPa,the maximum value was0.58 kPa in April,and the minimum value of 0.20 kPa was in July.?2?Average diurnal variation regularity of monthly net ecosystem exchange?NEE?during the whole year was strong,which showed a "U" or "V" type curve.The maximum value?negative?o f NEE occurred at around 12:00.NEE were positive in the night and before dawn,but negative in the daytime.And NEE in summer was much higher than that in winter numerically.In addition,monthly mean NEE were negative,which suggested that this forest ecosystem was acarbon sink.The maximum value-0.78mg·m-2·s-1 was in July,and the lowest value-0.22 mg·m-2·s-1 was in January.?3?From October in 2014 to September in 2015,the fitting relationships between monthly NEE and PAR values were better?R2>0.98?in the days of this forest ecosystem.Both the maximum net photosynthetic rate and dark respiration rate minimum values occurred in January,they were 2.072 mg·m-2·s-1?in January?and 0.367 mg·m-2·s-1?in December?,and the maximum values occurred in July,they were 10.945 and 2.392 mg·m-2·s-1,respectively.Fitting coefficients R2 of three typiacl plants between monthly Pn and PAR were higher than 0.97.The maximum values occurred in July,they were 15.491 mg·m-2·s-1?Daphniphyllum macropodum?? 3.110 mg·m-2·s-1?Cyclobalanopsis myrsinifolia?and 6.204 mg·m-2·s-1?Hydrangea macrophylla?respectively,and the minimum values were 0.075 mg·m-2·s-1?in January?and 0.007 mg·m-2·s-1?in December?.In addition,monthly canopy maximum net photosynthetic rate and dark respiration rate based on eddy covariance and eco-physiological method showed a good positive correlation?r =0.87,0.89?except Daphniphyllum macropodum,and the former was higher than the latter.?4?Monthly PAR and the net primary productivity during the day based on these two measurements showed a significant positive correlation?R2=0.95,P<0.01?.With the increase of Ta and relativity huminitity,the maximum net photosynthetic rate,dark respiration rate and apparent quantum efficiency of ecosystem showed an exponential increase,At the same time,with the increase of VPD,the maximum net photosynthetic rate,dark respiration rate and apparent quantum efficiency of ecosystem were showing a trend of decrease after increase at a turning point of 0.45 kPa,while the apparent quantum efficiency presented a decrease variation.