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چکیده
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Since the early 2000s, Persian oak forests in the Zagros in Iran have shown signs of decline. This study was designed to determine the relationships between crown dieback of Persian oak (Quercus brantii) with morphological and physiological leaf traits in two forest sites: Sheshdar (SH) and Gatchan (GA) in Ilam, Western Iran. Trees with increasing severity of crown dieback were selected from healthy to severely defoliated. Foliage samples were taken randomly from the crown on the slope‐aspect of the site. The results suggested that Q. brantii was not sensitive to drought effects during normal growth processes. There were variations in leaf physiological traits, however, in the different dieback classes at both sites. Foliage from declining trees at both sites had higher dry weights in contrast to the decreasing water contents associated with lower leaf areas in trees with severe defoliation from site GH. Chlorophyll pigments (Chl a and b) and carotene (Car.) were significantly lower decreased significantly in trees with moderate to severe defoliations from site GH, while in leakage from the foliage increased. A contrasting pattern occurred at site SH as accumulations of osmotic solutes (soluble sugars, total soluble protein and proline) increased significantly in foliage of severely defoliated trees, while at site GH, the total soluble protein and proline contents showed an upward trend until moderate defoliation. It was concluded that the physiological responses of Persian oak trees with dieback varied under extreme drought. Based on principal component analysis, leaf water status contributed most to the differences between dieback groups. It is concluded that physiological variations in oak foliage contribute to defence mechanisms enabling drought to be tolerated, maintaining essential life processes.
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