Özet:

Effects of drought stress on growth, predawn xylem water potential (ψ pd), osmotic solutes (soluble sugar and proline), and stomatal conductance were assessed in two oak ( Quercus cerris L. and Quercus robur L.) seedlings. Seedlings of both species were subjected to three drought treatments with the following irrigation intervals: well-watered (control: irrigation every 2-3 days), moderate drought stress (irrigation every 15 days), and severe drought stress (irrigation every 30 days). Drought-stressed seedlings of Q. cerris and Q. robur had more negative predawn xylem water potential than their well-watered seedlings. In Q. cerris, root collar diameter and root dry weights were negatively influenced by drought, while height, shoot dry weight, and root:shoot ratios were unaffected. Height and shoot dry weight of drought-stressed Q. robur were decreased, while root:shoot ratio increased. Drought caused significant decreases in stomatal conductance of both species. Q. cerris seedlings sustained higher stomatal conductance compared with Q. robur. Proline and soluble sugar increased in response to drought stress. Q. robur had a higher proline accumulation than Q. cerris. These findings suggested that the Q. cerris and Q. robur seedlings showed a drought stress adaptive mechanism either by restricting their growth or increasing root:shoot ratio or by decreasing water loss (reduced stomatal conductance) and accumulating of osmotic solutes.

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