Abstract:

Quercus variabilis is an important economic tree because it not only provides timber and firewood for local farmers, but also is used to produce cork, tannin extract, and edible fungi for commercial use. It is distributed in 22 provinces in China from sub-tropical to temperate regions and at altitudes that range from 50 to 2 000 m. It also plays an important role in the conservation of water and soil. However, little is known about the physiological tolerance mechanisms of drought stress. In order to discriminate among the drought-tolerant characteristics of different Q. variabilis provenances, we conducted a drought stress experiment using potted 3-year old seedlings of four provenances from different regions. Changes in superoxide dismutas activity (SOD), catalase activity (CAT), malondial dehyde content (MDA), electrolyte leakage rate, osmotic potential at saturation (ψπsat), osmotic potential at turgor loss point (Wπtlp), water saturation deficit at turgor loss point (WSDtlp), and modulus of elasticity (εmax) of leaves were measured and analysed as soil drought conditions developed. Under similar conditions of soil drought stress, provenance 4 (from Huanglong Mt. in the loess plateau) and provenance 3 (from the north slope of Qinling Mt.) revealed more antioxidant ability than provenance 2 (from Funiu Mt.) and provenance 1 (from the north slope of Bashan Mt.). During the development of soil drought stress, the MDA content and electrolyte leakage rate were enhanced to different extents in the four provenances; the greatest change was provenance 1 and the lowest change in provenance 4. The activities of SOD and CAT increased at the beginning of stress conditions but decreased at the end of the drought stress period. All provenances had the ability to maintain turgor and osmotic adjustment throughout the experiment but distinct differences among provenances were apparent: provenance 4 and provenance 3 had greater turgor maintenance and osmotic adjustment while provenance 1 performed the worst. Using Fuzzy synthetic evaluation of the parameters of water relations and the activities of two cell defense enzymes to water stress in leaves, the level of drought-tolerance among the four provenances decreased in the following order: provenance 4> provenance 3> provenance 2> provenance 1. Among the four provenances, provenance 4 was significantly different from the provenance 2 and provenance 1 (p<0.05). Differences in the drought tolerant characteristics of the four provinces resulted from long-term evolution and adaptation to their particular environmental conditions and are most likely genetically controlled. Therefore, these characteristics should be used for selecting and identifying drought tolerant provenances for use in forest management and restoration of Q. variabilis in arid regions.