Macronutrients Uptake and Nitrogen Utlization Efficiency in Dargazi Seedling and Pyrodwarf Clonal Pear Rootstocks Under Drought Stress Conditions

Using clonal rootstocks in modern temperate fruit orchards has expanded in recent years. Root system plays an important role in uptake of nutrients particularly under drought-stress conditions. Therefore, the present research was conducted to investigate the uptake and utilization efficiency of macronutrients in two commercial pear rootstocks (Dargazi seedling and Pyrodwarf clonal rootstocks) under drought stress conditions during 2019-21 in greenhouse and laboratories of department of horticultural science, Tarbiat Modares University, Tehran, Iran. The irrigation treatments were: control (100% FC), mild drought stress (60% FC), and severe drought stress (30% FC). The results showed that drought stress had different effects on the growth characteristics, uptake of nutrients in leaves and roots as well as traits related to nitrogen utilization efficiency of both pear rootstocks. In addition, decrease in nitrate reductase activity led to reduction in nitrate and ammonium content in the leaves of both rootstocks. The Pyrodwarf clonal rootstock under mild stress conditions had the highest root calcium content, total nitrogen accumulation, and nitrogen utilization efficiency which reflected in its better performance as compared to the Dargazi seedling rootstock. In contrast, the higher root: shoot ratio, root volume, root ammonium content, leaf calcium content, leaf nitrogen content, nitrogen efficiency ratio and nitrogen utilization efficiency in Dargazi seedling rootstock contributed to its better response to drought stress, particularly in severe stress conditions. These better responses could be attributed to differences in root systems in the two pear rootstocks which should be considered for selecting suitable rootstocks for establishment and management of pear orchards under drought stress conditions.