Abstract:

Gymnocarpos przewalskii originates from the Tethys Sea， and is a Tertiary relic of the desert area in central Asia. This species is very important for research on xerophyte evolution. Using 1-year-old seedlings of G. przewalskii as the experimental materials， we evaluated the responses of root morphological and physiological characteristics to drought stress in a pot experiment. Four water treatments were established， comprising a gradient corresponding to a control and light， moderate， and severe water stress （soil water content controlled at 45%-50%， 30%-35%， 15%-20%， and 5%-10% of field capacity， respectively）. The different soil water contents were maintained by regular weighing and re-watering pots to target weights. There were 10 replicates of each treatment. The seedlings were cultivated in pots in 2018 under these conditions， and the responses of the roots were analyzed. It was found that with increasing severity of drought stress， root length and root surface area significantly decreased. The root biomass decreased markedly under severe drought stress. Moderate and severe drought stress caused significant increases in the shoot：root ratio， specific root length， and specific root surface area of fine roots， and increased the ratio of bound water to free water. Drought stress led to a significant decrease in root vitality. As the soil water content decreased， proline content in roots initially decreased then markedly increased， while the soluble sugar and soluble protein content showed the reverse trend. Under drought stress， the concentrations of malondialdehyde， hydrogen peroxide， and the superoxide anion significantly increased， indicative of damage to the root membrane system. Root superoxide dismutase （SOD） activity markedly increased， peroxidase activity significantly decreased， and catalase （CAT） activity significantly increased under drought stress. In short， under drought stress， roots of G. przewalskii seedlings showed several morphological changes to increase their water-absorption efficiency， i.e.， the shoot∶root ratio， specific root length， and specific root surface area of fine roots all increased. The physiological changes in response to drought stress were a decrease in metabolism to reduce water consumption， active accumulation of organic solutes to decrease cell osmotic potential， and increases in SOD and CAT activity to reduce cell membrane damage.

Key words: water stress, Gymnocarpos przewalskii, root system, morphological characteristics, physiological characteristics