不同树形对龙安柚光合特性和果实品质的影响

Effects of Different Tree Shapes on Photosynthetic Characteristics and Fruit Quality of Citrus grandis var. Longanyou

摘要: 试验以龙安柚开心形、Y字形、双层分层形和自然圆头形4种树形为研究对象，测定各树形冠层不同部位的叶片光合特性及果实品质，并分析二者间的相关性。结果表明：1) 4种树形上部叶片的净光合速率(Pn)均高于下部叶片；一天中，Y字形不同部位叶片的Pn均高于其他树形，其次是开心形，说明Y字形和开心形光合能力较强。2) Y字形和开心形叶片的Chla、Chla/Chlb和SPAD含量均高于双层分层形与自然圆头形，而Chlb含量则相反；Car含量以开心形上部最高(0.61 mg∙g⁻¹)，Y字形上部次之(0.54 mg∙g⁻¹)，自然圆头形的叶片中含量最低。表明Y字形和开心形的捕光能力增强从而提高其光合效能。3) Y字形和开心形果实着色程度较好，单果重和可溶性固形物含量较高。开心形上下部Vc含量、总糖含量均较高，且可滴定酸(TA)较低。说明Y字形、开心形果实品质优于其他树形，且开心形冠层上部和下部的果实品质较为均一。4) Vc含量与Chla/Chlb (r = 0.838)和SPAD (r = 0.866)呈极显著正相关；Pn与果实转化糖及蔗糖含量、单果重、果形指数均呈极显著正相关，并与单果重的相关性系数最大(r = 0.712)。综上，龙安柚的Y字形、开心形冠层透光性好，叶绿素含量提高，树体叶片光合性能增强，有利于增加单果重，提高果实中糖和Vc含量，改善果皮色泽。

Abstract: Selecting reasonable tree structure can guarantee ventilation and light transmittance in the canopy, which is better for improving the rate of light utilization and high yield, quality or regular bearing. We used the open center shape, Y-shape, double layered shape and natural round shape of Citrus grandis var. Longanyou as the research object in this paper, and then photosynthetic characteristics and fruit quality in different position of four kinds of canopy were measured and their relationships were analyzed. The results showed that: 1) The net photosynthetic rate (Pn) of the upper leaves of four kinds of canopy was higher than that of the lower leaves. The Pn of the leaves of different parts of the Y-shape was higher than that of the other canopies in the day, followed by the open center shape. It is indicated that the photosynthetic abilities of Y-shaped and open center shape were better than the other two. 2) The contents of Chla, Chla/Chlb and SPAD in Y-shaped and open center shape leaves were higher than those in the other two, while the Chlb content was opposite. The two canopies with higher level of carotenoid content were the upper part of open center shape (0.61 mg∙g⁻¹) and Y-shape (0.54 mg∙g⁻¹), and natural round shape was the lowest. It is indicated that the higher light-harvesting abilities of Y-shape and open center shape enhance its photosynthetic efficiency. 3) The direct reasons for high fruit quality of Y-shape and open center shape were that their fruit peel coloration, soluble solids content and fruit weight were better or higher than those in other two. Moreover, the contents of Vitamin C (Vc) and total sugar were higher, and the titratable acid (TA) was lower in the fruits of upper and lower parts of open center shape, which indicated that its fruit quality was uniform. 4) There was a significant positive correlation between Vc content and Chla/Chlb (r = 0.838) and SPAD (r = 0.866). The Pn was positively correlated with fruit sugar and sucrose content, fruit weight and fruit shape index, and the correlation coefficient with fruit weight was the highest (r = 0.712). In conclusion, Y-shaped and Open center shape have obvious advantages such as better ventilation and light transmittance ability, higher chlorophyll content etc., which could enhance the photosynthetic performance and be beneficial to increase the fruit weight and improve the fruit quality.