2019 ASHS Annual Conference

Nutrient imbalances, and more specifically the relationship of potassium, magnesium and nitrogen to calcium, have been linked to physiological disorders in fruit like bitter pit in apples (Malus x domestica Borkh.). The use of isotopically labeled nitrogen, and nutrient analogs such as strontium and rubidium provide a direct quantification of uptake and distribution that is not possible with bulk mineral analysis. Here, the objective was to understand how abscisic acid (s-ABA), one of the major plant hormones that has been implicated in stress responses, influences nutrient uptake and partitioning between above ground and below ground parts of the tree. In this experiment, 10 atoms% ¹⁵N, Strontium (Sr), and Rubidium (Rb) were applied to Gala, Granny Smith, and Honeycrisp apple trees in 10 gallon pots in a split-plot design with cultivar as the main factor and were either treated with ABA 250 mg/L or 500 mg/L or an untreated control. Overall recovery rates of each tracer reflected the mobility of their nutrient analog. Strontium had an average tracer recovery rate of 3.9%, followed by ¹⁵N with 14.6% recovery and finally Rb with 15.1%. Independent of treatment, Gala significantly absorbed more tracer followed by Granny Smith and Honeycrisp for Rb and Sr but not ¹⁵N. However, treatments did not significantly affect tracer uptake. The ratio of Rb and ¹⁵N to Sr was the lowest for the control, followed by high concentration of ABA and then the low concentration of ABA. When considering root to shoot distribution, ¹⁵N and rubidium were higher in the roots when treated with ABA and lower in the above ground tissue. In the case of Sr, uptake was in such minute amounts no significance was seen based on treatment and distribution. These finding are consistent with previous literature showing the low mobility of Sr and high mobility of Rb and N. Here, a combination of tracers were used to identify scion-level variation in the response to manipulation of plant transpiration with exogenously applied ABA. These results have implications in the understanding of the link between plant transpiration and nutrient uptake and distribution in apple.