柑桔叶与果之间的水分转移:水势测定与氚水示踪的新证据

WATER TRANSFER BETWEEN LEAVES AND FRUITS IN CITRUS: NEW EVIDENCES FROM WATER POTENTIAL MEASUREMENTS AND TRITIATED TRACING

前人关于蒸腾的叶片从果中抽取水分的论点都是建立在间接推理上,而且试材多为离树的切枝。本研究采用四季桔或甜橙的完整植株,进行摘果与留果的叶水势变化比较,并将氚水注入果内,然后监测其转移,从而证实了水分由果向叶移动,为传统的“贮水库”假设,提供了最直接和确凿的新证据。但也指出,果实在水分竞争中并非总是处于劣势。在土壤干旱时果实的存在可能减弱叶水势的夜间回升程度。

The arguement that transpiring leaves withdraw water from fruits has been mainly founded on speculations,and based on experiments with excised shoots, and hence has been disputed. In the present studies, intact calamondin and sweet orange plants were used to compare leaf water potential changes resulted from removing or retaining the fruits. Moreover, tritiated water was injected into the fruits and traced for its moving directions. Direct and unambiguous proofs have been procured to show apparent water transfer from fruits to leaves under high illumi-nation, high temperature and low relative humidity, and hence high transpiration,but not under cloudy and rainy weather. The capability of transferring out water was greater for fruits of incipient or half ma-turation as compared to green or fully-matured ones. Water transferred out of fruits more intensely when leaf water deficits were not readily compensated by the limited water supply from roots subjected to stress. The above facts were in favour of the traditional concept of 'the fruit as a midday reservoir' . The fruits,however,did not seem necessarily to be always weaker in competition for water,since they might impede the fallen leaf water potential to recover during the evening and nocturnal period under drought conditions. ( 1 ) Former graduate student for MS} ( 2 ) Professor, reprint request^ ( 3 ) lecturer.