Abstract:

The physiological and biochemical responses of fine roots of Fraxinus mandshurica seedlings under drought stress were investigated. Under drought stress， vigor of fine roots with first or second order， membrane permeability， contents of soluble proteins， and activities of antioxidant enzymes (POD， SOD， and CAT) were examined. The results showed that both root vigor and soluble protein content decreased significantly and membrane permeability increased significantly by drought exposure in first and second order roots. The first order root changed more than the second order one. During the drought exposure， the activities of SOD increased at the beginning and then decreased at the severe drought stress. CAT and POD in fine roots of seedlings exposed to drought still 40 days further decreased significantly compared with 15 days and 30 days exposure,however their activities were the control higher than that in which had little variation. The results suggested that the abilities of antioxidant enzymes to scavenge the reactive oxygen species were weakened， resulting in an increase in lipid peroxidation and ion leakage， and a decrease in root vigor (r₂=0.45～0.58). It was included that compared with the second order fine roots， the first order fine roots had more physiological and biochemical responses to drought stress.

Key words: Fraxinus mandshurica, fine root, root order, drought stress