| Photosynthesis is the most valuable physiology reaction for fruit trees; almost 90％-95％dry material is formed through photosynthesis. Carbohydrogen came from photosynthesis is the basic material to form quality and quantity in fruit. The C4 pathway photosynthesis is more efficiency than C3 pathway, especially under stressful conditions, such as high temperature, drought and high photosynthetic active radiation(PAR). Citrus, as a evergreen fruit tree grown in semi-tropical, possessing a far lower net photosynthetic rate (Pn) than hardwood fruit tree and is shade tolerance. It is well known that exposing citrus trees to high temperatures and high PAR in summer could lead to reductions in Pn. Improving cultivation level is a good method to improve Pn for citrus; at the same time, as a typical C3 plant, improving C4 pathway photosynthesis in citrus will increase Pn more quickly. We studied the photosynthesis of different kinds of citrus planted in different environment and the C4 pathway enzymes in different citrus' green tissue, the main contents and results are as follow:1, Effects of different rootstocks on Satsuma Mandarin in photosynthesis under greenhouse condition. It was conducted with Guoqing No.4 Satsuma Mandarin three-year-old young tree whose rootstocks were Trifoliate [P. trifoliata], sexual hybrid Troyer Citrange[C. sinensis×P, trifoliata], Swingle Citrumelo[C. paradisi×P. trifoliata] and somatic hybrid Red tangerine+Trifoliate [C. reticuiata+P. trifoliata]. Studyed on the effects of rootstocks on the Pn through potted experiment in the green house, Results showed that: The diurnal variation of Pn in young tree with different rootstocks was seminar and presented bimodal carve; the first peak occurred at 10: 00, the second peak occurred after 13: 00 and the value was lower than the first one. With the analysis of Pn, transpiration rate(Tr), water use efficiency(WUE), apparent quantum yield(AQY) and carboxylation efficiency(CE), the results were the young tree--Troyer Citrange had a weaker photosynthesis, Trifoliate's photosynthesis was the best, red Tangerin+Trifoliate and Swingle Citrumelo was between the above two; Trifoliate had a higher physiological value in soluble protein, specific leaf weight and photosynthetic pigment; the other three didn't have remarkable difference. Under protected condition, Pn had obvious positive relationship with stomatal conductance(Gs),Tr and relative humidity(RH), Pn had obvious negative relationship with intercellular CO2 concentration(Ci).2, Photosynthesis of Satsuma Mandarin under nature condition. The photosynthesis of sunlit and shaded leaves in 'Guoqing No.4' Satsuma Mandarin whose rootstocks were Trifoliate was studied under nature condition. The results showed that, the diurnal variation of Pn in sunlit leaves from June to October presented bimodal curve, the first peak occurred at 9: 00, the second peak occurred at 14: 00-15: 00 and the value was lower than the first one. The diurnal variation of Pn present one peak curve in November and the maximum value occurred at 10: 00. In August, the diurnal variation of Pn showed one peak curve with the most value at 12: 00 and presented indention curve in June, July and from September to November. The sunlit leave showed higher Pn than shaded leaves. The sunlit and shaded leaves presented the similar seasonal variation, the maximum occurred at June, it were 8.8 and 4.2μmol m-2 s-1 respectively, and decreased in July, then increased from August to September and came to the second maximum value in September. After that, with a progressive decline in temperature, Pn decreased quickly and came to the minimum value in November, it were 2.55 and 1.65μmol m-2 s-1. In July, diurnal variation of AQY presented a midday depression pattern and CE showed one peak curve. The Pn at middle leaves was higher than at based and apical ones. After studied the photosynthetic of different types of shoot, the fruit-beating shoot have a better photosynthetic than nutritive shoot. Analysis all results, the main factors effected Pn of Satsuma Mandarin under nature condition is PAR, Ta, Gs and VPD.3, Activity of C4 pathway enzymes in different tissues of citrus. Hirado Buntan pummelo(C. grandis cv. Hirado Buntan), Cara cara navel orange(C. sinensis cv. Cara Cara) and Guoqing No.4 Satsuma Mandarin were used as experimental material. The activity of C4 pathway enzymes in citrus leaf at different time in different tissues, such as pericarp, fresh shoot and vein, were been assayed. The results showed that: There were C4 pathway enzymes activities at different time in leaf. The activity of PEPC declined at first and then increased and the maximum value occured in April 20; The activity of PPDK increased firstly and then declined, the maximum value occurred in May 1; The activity of NADP-ME declined all the time, Hirado Buntan pummelo showed significant higher NADP-ME activity than Cara cara navel orange and Guoqing No.4 Satsuma Mandarin all the time; The activity of NADP-MDH declined all the time too. The activity of C4 pathway key enzyme in pericarp, stem and fresh shoot were significant higher than in citrus leaf and lower or equals to in maize leaf. From higher to lower, the activity of PEPC and NADP-ME in different tisse was in pericarp, stem, fresh shoot and leaf, activity of PPDK was fresh shoot, pericarp, leaf and stem, activity of NADP-MDH was stem, fresh shoot, pericarp and leaf. It implied there be a C4 pathway photosynthesis in citrus, especially in pericarp, stem and fresh shoot, the high activity of C4 enzymes were very important.4, Photosynthesis in different kinds of citrus(cultivar). The photosynthesis of Lanelate navel orange(C. Sinensis cv. Lanelate), Star Ruby Grapefuit(C. Paradisi cv. Star Ruby), Sunburst tangelo(C. Reticulata×C. Grandis cv. Sunburst) and Jiangxi seedless Pnkan(C. Reticulata cv. Jiangxi seedless Ponkan) under nature condition were studied. The results showed that: in sunny and cloudy day, Jiangxi seedless Pnkan had the maximum Pn value, it were 8.8 and 7.6μmol m-2 s-1, and Lanelate navel orange had the minimum Pn value, it were 5.4 and 5.2μmol m-2 s-1, Star Ruby and Sunburst tangelo were between the above two; In overcast day, Pn among four kinds of citrus didn't show obvious difference. In sunny day, diurnal variation of Pn presented one peak curve in Lanelate navel orange and two peak curves in others, presented light "midday depression". In cloudy day, diurnal variation of Pn showed one peak curves in Lanelate navel orange and indention curve in others. In overcast day, all citrus presented one peak curve in diurnal variation of Pn and the maximum value occurred at 11: 00. Light compensation point in four kinds of citrus were 2.7-10.2μmol m-2 s-1, light saturation point were 1088-1139μmol m-2 s-1, dark respiration rate were 0.0104-0.3313μmol m-2 s-1, AQY were 0.023-0.0405, CO2 compensation point were 64.3-69μmol m-2 s-1, CO2 saturation point were 788-1421μmol m-2 s-1, photosynthetic capacity were 5.8-10.4μmol m-2 s-1, photorespiratory rate were 0.90-1.01μmol m-2 s-1, CE were 0.0139-0.0172 and the best temperature for Pn were 26.4℃-30.4℃. From those results, we can concluded that citrus possessed obvious characteristic of C3 pathway photosynthesis, at the same time, we also found very lower activity of C4 pathway enzymes (PEPC, PPDK, NADP-ME, NADP-MDH), it implied there maybe exists a limited C4-microcycle photosynthesis in citrus. |
