Studies On Photosynthetic Traits Of Tea Leaves At Different Positions Of Canopy And Their Seasonal Changes

As an important cash crop, the productivity of tea garden and quality of made tea are affected byphotosynthesis of tea leaves. In the latest couple of years, a lot of attention has payed to researches onphotosynthesis of tea leaves. To have a great insight into the overall understanding of tea plantphotosynthesis and seasonal changes of photosynthetic, physical and ecological indexes of tea leaves,develop a canopy structure with high yield and master the growth characteristics of tea plants,photosynthetic, physical and ecological indexes of surface canopy leaves with100%photosyntheticallyactive radiation （PAR）, middle canopy leaves with50%-70%photosynthetically active radiation （PAR）,low canopy leaves with less than15%photosynthetically active radiation （PAR） in late April, as well asthe seasonal changes being late April, mid-July, late September of these indexes of surface canopyleaves were studied in this paper. Through this study, the summary of the results were as the following:（1） Leaf temperatures were almost the same for different positions in tea canopy, butphotosynthetically active radiation （PAR） received were significantly different, air carbon dioxideconcentration （CO₂R） was the highest at low canopy.（2） Leaves of surface and middle, but not low canopy showed typical light response curves fittingwell to the Farquhar model. The light saturation points of surface, middle, low canopy leaves weredefined as1000、600、400μmol·m^-2·s^-1separately after analyzation.（3） Leaf mass area ratio （LMA）, total nitrogen （N_A）, total carbon （C_A）, chlorophyll contents basedon leaf area showed magnificent variation in the sequence of surface canopy> middle canopy> lowcanopy, but total nitrogen （N_M） and total carbon （C_M） based on leaf weight didn’t show any greatdifference.（4） The light-saturated photosynthesis rate （P_n）, stomatal conductance （G_s）, transpiration rate （Tr）also decreased markedly from surface to low canopy, while the concentration of intercellular CO₂（C_i）was the highest at low canopy. Photosynthetic nitrogen use efficiency （PNUE） of surface and middlecanopy were significantly higher than that of low canopy.（5） There was a very significantly positive correlation between the light-saturated photosynthesisrate （P_n） and stomatal conductance （G_s）, transpiration rate （Tr）, leaf mass area ratio （LMA）, but anegative correlation with the concentration of intercellular CO₂（C_i）.（6） Photosynthetically active radiation （PAR） surface canopy leaves received wasn’t of any greatdifference between late April, mid-July and late September; air carbon dioxide concentration （CO₂R）was the highest in late April, the lowest in mid-July; leaf temperature reached38.95℃in mid-July,31.22℃in late September，28.51℃in late April, showing great seasonal changes.（7） Light response curves of surface canopy leaves in different seasons all fit well to the Farquharmodel. The light saturation points of late April, mid-July, late September were defined as1000、1200、1200μmol·m^-2·s^-1separately after analyzation.（8） Leaf mass area ratio （LMA）, total nitrogen （N_A）, total carbon （C_A）, chlorophyll, metabolismproteins, structural protein contents based on leaf area showed magnificent variation in the sequence of late April> late September> mid-July.（9） Light-saturated photosynthesis rate （P_n）, stomatal conductance （G_s）, photosynthetic nitrogenuse efficiency （PNUE） of surface canopy leaves were greatly different in the sequence of late April <mid-July <late September, concentration of intercellular CO₂（C_i） were almost the same; seasonalchanges of transpiration rate （Tr） were of great difference with mid-July being the highest, late April thelowest; seasonal changes of water use efficiency （WUE） were magnificently different with late Aprilbeing the highest, mid-July the lowest.（10）According to seasonal changes of light-saturated photosynthesis rate （P_n）, and photosynthetic,ecological indexes of surface canopy leaves, the correlation analysis showed that tea leaf light-saturatedphotosynthesis rate （P_n） only significantly correlated with stomatal conductance （G_s）.