Abstract: Trunk spiral girdling was done on young 6-year-old trees of Litchi chinensis Sonn.‘Guiwei’in December in order to improve fruitset next year. During fruit development in May，effects of spiral girdling on photosynthesis and transpiration of leaves were investigated. The leaves were chosen from fruit-bearing and sterile shoots stemming from the same branch on the spiral girdling treatment or control trees. Trunk spiral girdling was useful for fruitset while fruits on the control trees fell down. The difference of photosynthetic parameters between leaves and no fruit leaves was narrowed by spiral girdling. Compared with the control，the maximum leaf photosynthetic rate（Amax），apparent quantum efficiency （AQY）and carboxylation efficiency（CE）were significantly reduced while light compensation point（LCP）was increased. It was deduced that spiral girdling decreased photosynthetic efficiency. Based ondiurnal variation of net photosynthesis（Pn）and transpiration（Tr），it was indicated that the extent of reduced Tr was more serious than Pn by spiral-girdling treatment. Pn was significantly relevant with Tr. Diurnal curves of Pn and Tr of the control exhibited a single peak at 14：00. Pn and Tr of the treatment were shown a clear midday depression mainly caused by stoma limitation. The daily average of Pn and Tr of fruit-bearing leaves were higher than non-fruit-bearing leaves from the same treatment. It was suggested that fruit stimulate the increase of Pn and Tr.

Key words: litchi, spiral girdling, fruitset, net photosynthesis, transpiration