| چکیده انگلیسی مقاله |
The monitoring of the physical and chemical characteristics of the soil as well as the changes in leaf nutrients, which are important in drought stress conditions, is effective in managing the dieback phenomenon of Iranian oak trees (Quercus brantii Lindl.). This research was carried out in 2019-2021 in Ilam in the western Iran between geographical coordinates of 33o, 44/, 26// to 33o, 46/, 01// N and 46o, 10/, 46// to 46o, 15/, 25// E. In order to investigate the condition of soil horizons, soil profiles were dug. Then, five healthy trees and five declined trees were considered. Soil samples were taken from two soil depths, including 0 to 30 and 30 to 60 cm, in the north and south slopes from the under-canopy of the trees, and for each tree, a leaf composite sample was taken. The tested characteristics include electrical conductivity, saturated soil acidity, calcium carbonate, total nitrogen, available phosphorus, potassium, calcium, magnesium, iron, zinc, manganese, and copper and nitrogen, phosphorus, potassium, calcium, magnesium, and iron, zinc, manganese and copper were determined in the leaves of oak trees, which are mentioned in this article. The obtained data were analyzed using SAS software. The results of variance analysis of the data showed that some of the changes in the physical and chemical characteristics of the studied soil at different depths and slope directions had significant differences (p<0.05). Regarding the soil texture, the comparison of the means showed that the percentage of silt in the first and second depth in the north direction was the highest with values of 38 and 39% in the places of healthy trees and the lowest in the first depth in the south direction in the places of declined trees with 30%. The saturation percentage and apparent specific gravity decreased and increased, respectively, with the change of location from the location of healthy trees to the declined trees location. Also, the amount of lime, which affects the availability of nutrients, increased from the location of healthy trees to the location of declined trees. Thus, in the case of phosphorus, potassium, zinc, manganese and iron, a decreasing trend was observed and only in the case of copper, an increasing trend was observed. A decreasing trend in the properties of organic carbon, potassium and zinc in the soil and in the concentration of potassium and zinc elements in the leaves in the places of declined trees compared to the places of healthy trees, the need to pay attention to the preservation of organic carbon and the management of potassium nutrients. Determining the important characteristics of the soil in terms of trees' tolerance to unfavorable environmental conditions, especially lime as a negative factor and nutrient elements such as potassium and zinc as positive factors, can help in better forest management. Due to the aggravation of the declining of trees in the conditions of nitrogen, potassium and zinc reduction, it is necessary to maintain organic matter, foliar application of zinc and potassium elements, especially in new plantations.
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