Objective To study the effects of different drought stress on leaf structure of Camellia oleifera, in order to understand the mechanism of drought adaptation.

Method 7-year-old C. oleifera 'Changlin-4'forests were tested by applying four levels of drought stress which soil moisture contents were kept as 15%-20% (severe drought stress), 20%-25% (moderate drought stress), 25%-30% (mild drought stress) and the control (natural condition). The leaf external morphological characters, stomatal characters of leaf lower epidermis, microstructure of mesophyll and main vein were measured by making paraffin sections, temporary sections and microscopic observation system.

Result The results showed that the leaf fresh weight, leaf dry weight, and saturated weight of C. oleifera declined with the decreasing of soil moisture, the drought stress significantly reduced the leaf thickness and leaf size, the stomatal area, perimeter, aperture, apparatus length and width of leaf lower epidermis also decreased significantly, the stomatal density decreased at first and then increased. As the drought stress became more intense, the thickness of leaf upper and lower epidermis decreased significantly, the upper and lower cuticle thickness increased significantly, the thickness of palisade tissue and the ratio of the palisade tissue and spongy tissue decreased significantly. As drought stress intensified, the thickness of the main veins of the leaves and the midrib protuberant degree increased significantly, the thickness of xylem under moderate drought stress and short diameter of vascular bundle under moderate and severe drought stress were significantly lower than that of the control, different treatments of drought stress had no significant effect on the thickness of phloem.

Conclusion All of these changes in the leaf structure of C. oleifera were ecological adaptations to drought stress.C. oleifera could adjust the leaf structure to maintain their survival and growth based on the water deficit, indicating that C. oleifera has strong adaptability to drought stress.