Abstract: With a splitplot experimental design, this paper studied the effects of different pruning intensities (no pruning, CK; light pruning, cutting 25% of whole canopy; moderate pruning, cutting 33.3% of whole canopy; and heavy pruning, cutting 50% of whole canopy) on the growth and photosynthetic physiology of Eucalyptus urophylla × E. grandis. Pruning intensity had no significant effects on the diameter at breast height, tree height, and single tree volume. In the main plots, the diameter at breast height under heavy pruning was almost the same as that of CK, and was larger than that under light pruning and moderate pruning. The tree height in all treatments was basically the same, and the single tree volume had the same variation trend as the diameter at breast height. Heavy pruning had the best promotion effect on the tree growth in the 1st pruning practice. After carrying out the 2nd pruning practice, the tree growth under heavy pruning-heavy pruning, heavy pruning-no pruning, and no pruning-no pruning was slightly better than that in other treatments. Under the four pruning intensities, the net photosynthetic rate had the same variation trend as the tree growth rate, being mainly affected by instantaneous carboxylation efficiency. The transpiration rate was not changed with pruning intensity. The water use efficiency had the same variation trend as the tree growth rate, and the variation was mainly induced by the difference of net photosynthetic rate. Considering the water use efficiency, maximum growth, and length of wood without knot, it was suggested that the heavy pruning-heavy pruning could be the best manual pruning mode for the cultivation of E. urophylla×E. grandis.

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