Study on Photosynthetic Response Curves of Cyclobalanopsis glaucoides

The photosynthetic characteristics and photosynthesis potential of Cyclobalanopsis glaucoides under conditions with different photosynthetic active radiation (PAR) and CO2 concentration (Ci) were studied by taking 14yearold Cyclobalanopsis glaucoides grown on the campus of Southwest Forestry University as study objects, and the response curve of net photosynthetic rate (Pn) to photosynthetic active radiation (PAR) and CO2 concentration (Ci) were measured in situ by using a LI-6400 portable photosynthesis system with 6400-02B LED light source and CO2 steel cylinder. The important photosynthetic parameters including the apparent quantum yield (Q), maximum photosynthetic rate (Pmax), dark respiration rate (Rd), light compensation point (LCP), light saturation point (LSP), apparent carboxylation efficiency (Vc), maximum electron transport rate (Jmax), light respiration rate (Rp), Maximum carboxylation efficiency (Vcmax), rubisco content (Rubisco), CO2 compensation point (CCP), CO2 saturation point (CSP) were fitted and estimated. The results showed that the net photosynthetic rate (Pn) increased rapidly when the PAR value was under 200 μmol/(m2 s), then the Pn grew slowly till reached the maximum value, afterwards it dropped slightly when the PAR value was above 800 μmol/(m2 s). The photosynthetic CO2 response (Pn/Ci) curves of C. glaucoides showed that Pn value increased fast when Ci was under 400 μmol/mol, then it grew gradually till it reached saturation status as Ci increased. Both of the LCP and LSP values of C. glaucoides were lower, indicating that this tree species was of shade tolerant characteristics. Moreover, the study showed that the photosynthetic capacity of C. glaucoides was lower because of the lower Vc, Jmax, Vcmax and Rubisco values. Based on the characteristics of this tree species, it was proposed that C. glaucoides should be planted on the half shade slope, shade slope and/or other appropriate shade habitat conditions at limestone region in the middle area of Yunnan Province.