| Forest biomes play an important role in regulating the exchange of carbon cycle between the atmosphere and the terrestrial biosphere. Furthermore, green leaves are the fundamental units of forest carbon exchange, and their photosynthesis (A) and respiration (R) mainly drive this process. Thus, the sensitivity and acclimation of foliar eco-physiological processes to warming make an efficient way to forecast the carbon balance of forest vegetation in the future. To estimate the effects of global warming on the leaf carbon exchange of Chinese broad spruce forests, the carbon exchange characteristics (mainly A and R) of seven spruce taxa (Picea. koraiensis, P. meyeri, P. wilsonii, P. crassifolia, P. asperata, P. likiangensis var. balfouriana, and P.likangensis var. linzhiensis) under control (25/20℃, day/night) and simulated wanning treatment (35/25℃) were compared in this thesis.The main results are as follows:(1) The variation in the CO2 assimilation rate at each growth temperature (Agrowth) was different between different spruce taxa:except for P. meyeri and P. crassifolia,Agrowth were significantly decreased in other five taxa under warming treatment. This result may be attributed to the different ways of acclimation in photosynthesis to warming, which is detected by the temperature curve for photosynthesis. The temperature optimums for A (Topt) in P. koraiensis, P. meyeri, P. wilsonii, and P. likiangensis var. linzhiensis were non sensitive to warming treatment, while Topt in other three spruce species obviously increased. However, A at Topt (Aopt) in P. koraiensis, P. meyeri and P. crassifolia showed no significant variation, compared to significant decrease in other four spruce species. In addition, the maximum photochemical efficiency of PSII (Fv/Fm) in P. koraiensis, P. wilsonii, P. asperata, P. likiangensis var. balfouriana, and P.likangensis var. linzhiensis were also significantly decreased, suggesting that the inhibition of photosynthetic activity in these five species occurred under warming treatment.(2) Species-specific differences of Rgrowth were found in seven spruce species:P. crassifolia, P. asperata, P. likiangensis var. balfouriana, and P.likangensis var. linzhiensis showed no significant variation of Rgrowth under warming treatment, while others exhibited obvious increase. These differences in seven species were mainly attributed to the different degree for acclimation of respiration, which was detected by the temperature curves for respiration. Q10 (i.e. proportional change in R with a 10℃increase in temperature) in P. crassifolia, P. asperata, P. likiangensis var. balfouriana, and P.likangensis var. linzhiensis showed significantly downward, while others were no sensitive to temperature.(3) Except for P. crassifolia, other six species showed increasing R/A under warming treatment, suggesting that the response of R/A to growth temperature varies with species. The increase of RIA ratio was attributed to various potential for photosynthetic and respiratory acclimation.In summary, we concluded that (1) in warming treatment, P. crassifolia displayed a strongly hoemstatic RIA ratio. In other words, in P. koraiensis, P. meyeri, P. wilsonii, P. asperata, P. likiangensis var. balfouriana, and P.likangensis var. linzhiensis, the CO2 exchange is highly sensitive to warming treatment. (2) The mechanism of acclimation in photosynthesis and respiration of spruce species was species-specific and more complex. (3) Compared with photosynthesis, acclimation of respiration is more sensitive to warming temperature. (4) The asynchronous acclimation of respiration and photosynthesis to temperature results in the change of carbon exchange. All results showed that the different shifts of photosynthesis and respiration to increasing temperature would lead to the reduction of potential negative feedback in the carbon cycle in most spruce forest. |
PDF Full Text Request