Multi-elemental isotope and analog tracer application to measure nutrient uptake and distribution in Malus × domestica Borkh.

Plant nutrient uptake is critical to maintain an optimum balance between vegetative and reproductive growth and fruit quality. Nutrient imbalances, and more specifically the relationship of potassium, magnesium and nitrogen to calcium, can be critical for fruit quality in apple (Malus × domestica Borkh.). In perennial plants, it is difficult to conduct short-term experiments to measure plant uptake and distribution in response to either cultivar or treatment because of substantial preexisting nutrient pools already present. The use of isotopically labeled nitrogen, and nutrient analogs such as strontium and rubidium allow for the quantification of uptake and distribution that is often not possible with bulk mineral analysis. Here, the objective was to understand how scion genotype influences nutrient uptake and partitioning between aboveground and below ground parts of the tree. In this experiment, 10 atom% ¹⁵N, strontium (Sr), and rubidium (Rb) were applied to three different potted apple cultivars compared to an untreated control. After 70 days of growth, 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. These results have implications in understanding the association between aboveground factors like transpiration and nutrient uptake and distribution in apple.