The phase changes in floral induction, evocation and differentiation take place in litchi. In order to elucidate the physiological changes during the phase changes, the photosynthetic rate (Pn), chlorophyll index (SPAD), fluorescent parameters, carbohydrate and nitrogen contents of litchi leaves in the field were studied with 'Feizixiao', a early-medium cultivar, and 'Guiwei', a medium cultivar. Results showed that the flowering progress of the 'Feizixiao' litchi trees was earlier than that of 'Guiwei'. But the related physiological indexes of two cultivars had similar change trend during the flower bud differentiation. During the flowering, the changes of Pn and SPAD were lower at floral induction and heading stage, higher at the stage of"whitish millets" and alabastrum, but the fluorescent parameters were just opposite to them. At the "whitish millets" stage, the contents of the soluble sugars were the lowest, whereas starch and total nitrogen were the highest. Therefore, the changes of photosynthetic characteristics and carbon-nitrogen content were greatly influenced by the flowering phase, and the period of "whitish millets"was the key turning point of the changes of carbohydrate and nitrogenous compounds in litchi.%荔枝花芽分化分为诱导、 发端和分化3个阶段.试验以早中熟品种'妃子笑'和中熟品种'桂味'为试材,对荔枝花芽分化不同物候阶段叶片净光合速率(Pn)、 叶绿素指数(SPA D)、 荧光参数和碳氮物质等生理指标的变化规律进行研究.结果表明:'妃子笑'的成花进程早于'桂味'品种,但2个品种在整个花芽分化期间的相关生理指标均呈相似变化趋势,Pn和SPA D在诱导期和抽穗期水平较低,"白点"期和花蕾期有所增加,而荧光参数恰好相反;荔枝成花期间,其可溶性总糖含量在"白点"期阶段水平最低,而淀粉和总氮含量呈相反趋势,在"白点"期达到最高值.可见,不同荔枝品种的光合特性与碳氮物质变化受其花芽分化的阶段性影响更大,而"白点"期是荔枝碳氮物质变化较为关键的转折点.
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