Variation in Anatomical Properties and Hydraulic Conductivity of Persian Oak (Quercus brantii Lindl.) Trees Affected by Dieback

The present study aimed to investigate the anatomical properties of wood and xylem functioning of Persian oak affected by crown dieback.

Affected Persian oak trees were categorized into four different classes based on the severity of crown dieback (healthy, slight, moderate, and severe trees) with three replicates. The target trees were randomly selected from three forest stands. Branch samples at the age of 4-6 years were randomly taken from the trees’ crowns and the anatomical traits such as tree ring width (TRW), vessel density (VD), average vessel size (AVS), and relative specific conductivity (RSC) were determined. One-way ANOVA and LSD comparison of means were used to analyze the data and their mean comparison.

The results showed that oak trees are using different hydraulic strategies in different habitat conditions. The effect of severity of canopy dieback on xylem anatomical traits was significant. The narrowest ring width as 257.67, 365.56, and 159.17µm was observed in trees with a severe degree of dieback (with more than 66% canopy dieback). The RSC was decreased in response to reduction in the vessel size (2905.7µm2) and density (26.09mm-2) for declining oak trees from the last site. The AVS was increased in moderate and severe degree of canopy dieback from two sites, resulting in enhanced conducting efficiency. Whoever, their resistance decreases because of the risk of cavitation.

Healthy oak trees showed the highest values of RSC and VD. However, the AVS was not increased. The results suggest that larger and more abundant vessels would allow for more efficient water transport. However, these larger vessels may also promote a greater risk of cavitation during a drought that illustrates the tree's incompatibility with water deficit stress.