光合有效辐射对不同柑桔品种之光合生产与结实的影响

研究了山田温州蜜桔、雪柑、椪柑之树冠中光合有效辐射(PAR)的分布以及PAR对树体光合能力和结果等的影响,发现树体叶幕内相对PAR充足的部位,叶片着生直立,总叶面积较大,叶片的光合能力较强,果实着色较艳,品质较优,山田温州蜜柑、雪槽和椪柑树冠优质果之着生部位分别相当子相对PAR大于32.％、21.5％和18.5％的部位,而相对PAR小于16.2％、16.9％和13.4％的部位,则分别为它们的低效或无效光合生产区。另外,根据测得的资料,提出了各类柑桔树的适宜的叶面积指数。

DISTRIBUTION OF PHOTOSYNTHETICALLY ACTIVE RADIATION WITHIN TREE CANOPIES AND THEIR EFFECTS ON PHOTOSYNTHESIS AND FRUIT QUALITY

The distribution of photosynthetically active radiation(PAR)within tree canopies of three different citrus species was investigated to give an understanding of the effects of PAR on photosynthetie production and fruit quality.In any section of a canopy where plenty of PAR was present,leaves tended to be vertically directed.Canopy strata nomally exposed to higher PAR had smaller leaves,larger aggregate leaf area and higher photosynthetic rates as compared with those parts receiving lower radiation.An abundance of PAR favoured the accumulation in fruits of vitamin C,total sugar and soluble solids,and hasten the coloration of fruit skin.Citrus unshiu,C-sinensis and C.reiiculala were shown to differ in their PAR requirements for leaf subsistence and fruit bearing.Taking the relative intensity of PAR in the open field as 100,any space within a C.unshiu tree canopy where the relative intensity of PAR was below 16.2% would be photosynthetically ineffective.The corres- ponding values for C.sinensis and C.reticulata were 16.9% and 13.4% respecti-velly.It is suggested that,as a practical guide in citrus culture,the thickness of the green-leaf layer should be kept within 1.2 meters for C.unshiu and 2 meters for both C.sinensis and C.reticulata through the application of prunning and dwarfing technique,and the optimal leaf area indices for them were estimated at about 5.0,5.5,and 6.0 respectively.