Abstract: The diurnal variations of net photosynthetic rate andits impact factors such as photosynthetic active radiation,leaf temperature,andleaf water vapour deficit (p_pdl) of Eucalyptus GL₉ in differentseasons werestudied by Li-6400 portable photosynthesis system.The results indicated that the diurnal net photosynthetic rate of Eucalyptus was a “double peaks” curveinspring and summer,while it were two different styles of “single peak” during in autumn and winter.The trend of average net photosynthetic rate of Eucalyptuswas 10.248 μmol·m^-2·s^-1 in spring＞7.349 μmol·m^-2·s^-1 in summer＞3.645 μmol·m^-2·s^-1 in autumn＞2.505 μmol·m^-2·s^-1 in winter.The net photosynthetic rate andphotosynthetic active radiation in the four seasons showed a great deal of synchronization,but photoinhibition of Eucalyptus occurred when photosynthetic active radiation got more than 800 μmol·m^-2·s^-1 and kept sharply increasing.The diurnal regularity of both leaf temperature and p_pdl hadbest stabilities in spring,autumn and winter,while it had a greater fluctuation in summerwith higher datas.

Key words: Eucalyptus, net photosynthetic rate, photosynthetic active radiation, leaf temperature, leaf water vapour deficit, diurnal change