Variability of nitrogen and phosphorous in Persian oak trees and soil of dieback affected stands in Ilam

This research was performed to study the variability of nitrogen and phosphorus nutrients in leaf, root and soil around the root of dieback affected Persian oak trees during two years in spring and summer in Melah-Siah region, Ilam province. Oak trees were divided into four groups with six replicates based on the severity of crown dieback. Sampling of leaves, roots and soil of trees was randomly performed in four directions of tree crown and were transferred to the laboratory for analyzing the nutrients. Results showed that the leaf nitrogen amount of dieback trees in spring and summer of 2013 was more than those of healthy trees. The leaf phosphorus amounts of dieback trees in spring 2013 and spring 2014 were less than those of the healthy trees. The root nitrogen amount of dieback trees in spring and summer 2013 was more and in spring 2014 was less than that of healthy trees. The root phosphorus amount of dieback trees was less than that of healthy trees in all sampling seasons. The results showed that N had declining temporal changes. But temporal change of P was increasing. The concentrations of N and P in leaf were also more than the root. It is concluded that drought has significant effect on the mentioned elements status in oak trees. Resisting to drought conditions and possibly performing the vital activities are the reasons for element status changes in the dieback trees.