Carbon Fluxes And Their Response Mechanisms In A Phyllostachys Edulis Ecosystems In Anji County,Zhejiang Province

In this study,eddy covariance system,CO₂ profile system and meteorological gradient system were used for long time observation of Phyllostachys edulis forest ecosystem in Anji,obtaining CO₂ flux and meteorological data from 2011 to 2014,and CO₂ profile data in May to October,2011.And then combined with the leaf area index（LAI）and leaf maximum net photosynthetic rate（Pm）during2011^-2012,we analyzed the characteristics of spatial and temporal variations of CO₂,carbon storage of canopy and carbon flux variation at different time scales in this Phyllostachys edulis forest ecosystem,as well as the influence factors and the effect of seasonal drought and high temperature on the carbon fluxes.Results showed that:（1）The CO₂ concentration of bamboo forest during the growing season exhibited obvious time variations,as well as vertical variations.In the entire growing season,the minimum CO₂ concentration of the forest appeared in July(368.1 μmol·mol^-1),and the maximum one emerged in October(402.6μmol·mol^-1).The vertical gradients in and above the canopy showed a consistent variation trend:positive in the daytime（carbon sink）and negative at night（carbon resource）.However,the CO₂ vertical gradients below the canopy were negative throughout the day.We found the proportion of the CO₂ storage flux obtained from the profile system to net ecosystem CO₂ exchange（NEE）was 25.5% and8.9% at a half-hour and daily scale,respectively,but was only 0.22% at a monthly scale.The result suggested that CO₂ storage flux could not be neglected when NEE was estimated at a half-hour or daily scale,but could be ignored at a monthly or longer time sale.（2）For Anji Phyllostachys edulis forest ecosystem in these four years,the average value of NEE was-586.85 gC·m^-2·y^-1(±55.53 gC·m^-2·y^-1),and GEE average value was^-1526.35 gC·m^-2·y^-1(±65.39 g C·m^-2·y^-1).Because of shooting in on year and leaf changing in off year,both of them approximately showed a double peak curve every annually.Seasonal variations of RE were controlled mainly by temperature,with a single peak curve each year,and the average value of these years was 939.50 g C·m^-2·y^-1(±18.55 g C·m^-2·y^-1).Compared with the carbon sequestration capacity of main forest ecosystems in China,this Phyllostachys edulis forest had a high carbon sequestration capacity,and a good stability.（3）There was an obvious difference between the fluxes in on and off year of this Phyllostachysedulis forest.Because of leaf changing and the photosynthetic capacity of old leaves decreasing in off year,NEE of January to May were lower than those in on year over the same period.After May,in off year,since the LAI and the photosynthetic capacity of new leaves increased,NEE were slightly higher.（4）Temperature（Ta and Ts）and PAR were the main environmental factors that affected the carbon flux of Phyllostachys edulis forest.Besides,the soil moisture and VPD were not significantly correlated with NEE（P>0.05）,but under certain conditions,NEE could be restricted.The correlations of LAI and Pm with NEE also reached a very significant level（P<0.01）.（5）LAI and Pm were the main influence factors of monthly NEE differences in on and off year.When LAI and the maximum net photosynthetic rate reduced by 1 and 1 mgCO₂·m^-2·s^-1 each time,NEE was reduced by 22.699 gC·m^-2·mon^-1 and 12.749 gC·m^-2·mon^-1,respectively.（6）The seasonal high temperature and drought in July and August 2013 due to the unsynchronized of precipitation and heat,caused the NEE decreased significantly in the two month,and compared to the same period in 2011,the decreased range were 59.9% and 80.0%.In addition,the atmosphere temperature were significant correlative with RE and GEE in 2011 and 2013（P<0.05）based on the analysis for the relationships among the NEE,RE and GEE with environmental factors.For the air and soil moisture,RE and GEE had different response,GEE is more vulnerable decrease to the soil moisture compared to RE.The raising of saturation vapour pressure promoted the RE but inhibited the GEE,which is supposed the main reason for NEE decreased of bamboo forest ecosystem in Anji from July to August 2013.