Photosynthetic Characteristic Studies Of Main Pumelo (Citrus Grandis Osbeck) Varieties

Photosynthesis of peripheral and inner leaves of pomelo trees (Citrus grandis) were studied under field conditions on three varieties: Shatianyou, Guanximiyou, and Sijiyou. Results were shown as follows:1.Diurnal variation of net photosynthetic rate (Pn) of peripheral spring-shoot-leaves without fruit (psp) presented double-peaked curve; diurnal Pn variation of inner spring-shoot leaves without fruit (isp) showed one or two peaks, indention or flag carve; diurnal Pn variation of peripheral autumn-shoot-leaves without fruit presented single or double-peaked curve. Analysis on averaged maximal value and averaged daily Pn showed that Shatianyou ranked first, followed by Guanximiyou and Sijiyou.2. There was saturated effect of Pn in response to light intensity and CO2 concentration. The light compensate and saturated points of Pomelo leaves were 15.74-78.31 mol m-2 s-1 and 1056-1821 mol m-2 s-1, respectively. The apparent quantum efficiency were between 0.01725 and 0.05431. Data therefore showed that the leaves of pomelo verities had the higher utilization efficiency on weak light and strong light. The CO2 compensate and saturated points were 50.99-97.31 mol mol-1 and 800-961 mol mol-1, respectively. Carboxylating efficiency was between 0.01769 and 0.05340, which indicated that pomelo varieties had obvious character of C3 type plant. The proper temperature for photosynthesis was 24-34 , temperature adaptability of psp was better than isp. It is likely that there were relations between temperature adaptability and temperature during leaves forming. At the same time, adaptability of Shatianyou was better than the other verities.3. Under field conditions, seasonal variation of Shatianyou is more obvious than that of the other two. The seasonal variation of Guanximiyou is similar to that of Sijiyou, whose Pn value in October is the highest while in August is the lowest.4. It was the best to analyse relations between Pn of pomelo varieties and Physio-ecological factors by path analysis and stepwise regression combination. The former is qualitative analysis, while the latter is quantitative analysis. Results indicated that the influence of physio-ecological factors on Pn had levity, complexity, and instability.5. There were no remarkable relation between Pn and chlorophyll content, and between specific leaf weight.