Abstract: Drought is an important environmental factor restraining the distribution and growth of southern-type poplar clones. Sex-specific poplar clones may have different tolerance and corresponding physiological responses to drought stress. In this study, we compared the sex-specific response to continuous drought stress and rewatering in a pot experiment using one-year-old cuttings of male (Populus deltoides ‘Nanlin 3804’) and female (P. × euramericana ‘Nanlin895’) southerntype poplar clones. The results showed that continuous drought significantly restrained the growth of both female and male poplar clones. Under continuous drought stress, membrane lipids of leaf cells and tissues sustained peroxidation, which led to the destruction of membrane system. Furthermore, leaf MDA content, antioxidant enzyme (SOD and POD) activity, and free proline content increased significantly under continuous drought before plant death. Under severe drought, the leaves of both clones lost water quickly, with a “concentrated” phenomenon of chlorophyll. Compared to female clone, the above-ground biomass of male clone was lower, while root biomass increased under continuous drought, thereby enhancing its water absorption capacity and reducing transpiration and water loss. Meanwhile, male clone increased the antioxidant enzyme activities in leaves earlier and more greatly, and kept for much longer period, than female clone. Such differences alleviated the peroxidation of membrane lipid, maintained normal physiological functions of cells and tissues, and delayed plant death. After re-watering, the male clone recovered to normal physiological state more quickly, which ensured its higher growth than female clone. In general, male clone of southern-type poplar showed relatively stronger drought tolerance than female clone, thus it could be used for afforestation in mountainous areas.

Key words: photosynthetic characteristics, dry matter accumulation and allocation, water use efficiency., tillage practices, grain yield