Effects of drought stress on physiological and biochemical adaptation responses in young black locust Robinia pseudoacacia L. clones

Black locust Robinia pseudoacacia L. is a fast growing tree, used in forest establishment. It is an economically important tree for tool production, obtaining timber and fuel as well as an important constituent element for landscapes. Though the tree is abundant, information on genetics, physiology, biology, wood quality and adaptability to different ecological conditions is limited and fragmented. The aim of this research was to study physiological and biochemical adaptation by comparing two black locust Clones that showed different responses to drought. The two Clones were exposed to different water regimes: Medium Stress and High Stress (50 and 25 % of water supplied to control). Physiological and biochemical measurements were made. Stress affected negatively the growth of both Clones. The effect of different stress intensity (MS and HS treatments) was observed on stem shape. When re-watered the stem showed partial recovery. Net photosynthesis rate in drought period did not show marked difference between the Clones. After soil rehydration both Clones recovered photosynthesis level. The Clones 1 did not show differences in osmotic potential when comparing Control and MS or HS trees. The Clone 2 showed increased osmotic potential in relation to stress intensity. The maximum potential in Clone 2 was comparable to the values for Clone 1. Amino acids, especially proline, increased in drought. The soluble sugars increased during the stress period in the stems of Clone 2. The increased absence of osmolytes increase in Clone 1 could be due to the absence of adaptive mechanism. Alternatively, osmolytes concentration was already too high to be increased more by drought. Different osmotic potential and changes during drought can be related to the growth during tree life. Selection of Clones according to osmolyte index could to select better trees for different climate zones.