Contrasting foliar and soil nutrients responses to drought induced crown dieback in a Quercus brantii forest

Evidence has shown that drought-induced crown dieback has significant interaction with soil-plant water and nutrients relationships, but there isn’t sufficient knowledge of the water and nutrients connections in declining Persian oak (Quercus brantii) trees. To investigate the relationships between crown dieback and leaf nutrients concentrations, leaf water content, soil nutrients concentrations and soil mois­ture, one of the dieback affected stands was selected. This stand was located in Shalam forested area in northern Ilam province, west of Iran. Persian oak trees were evaluated using a crown dieback classification and divided into four classes with four replicates based on the severity of crown dieback. Sampling from leaves of trees and soil was implemented randomly in four sides of tree crown in August. Trees with mod­erate to severe declining showed reduced leaf water content (WC) and reduced relative leaf water content (RWC). Leaf N and P concentration of declining trees was significantly (p-value <0.05) more than that of healthy trees. The leaf K concentration of declining trees was significantly (p-value <0.10) more than that of the healthy. The leaf N:P amounts of oak trees was statistically different among crown dieback classes. But no significant differences was observed between the healthy and declining trees in terms of soil N, P, K, Ca and Mg concentrations and soil moisture. It was concluded that drought has effects on the nutrients status in the leaves of Persian oak trees and their changing in the declining trees is for resistance to drought condition, improving water use efficiency and possibly performance of vital activities.