Thursday, August 11, 2016
Georgia Ballroom (Sheraton Hotel Atlanta)
Zinc (Zn) deficiency is common in pecan trees in the Southwestern US where soils typically have alkaline pH. At maturity Zn-deficient pecan leaves exhibit low total lamina area thickness, interveinal chlorosis, and reduced photosynthetic capacity. Low canopy-wide photosynthesis due to Zn deficiency is expected to negatively impact dormant season carbohydrate reserves. Our objective was to characterize effects of soil-applied Zn-EDTA on carbohydrate storage in shoots and roots of non-bearing ‘Wichita’ pecan. The study orchard, which has alkaline and calcareous soils, was planted in 2011. Over the course of each growing season from the time of planting 0 (control), 2, or 4 kg.ha-1 Zn were applied through microsprinklers as Zn-EDTA. Plots were arranged in a randomized complete block design with four blocks. Mid-season leaf tissue Zn concentrations for the 0, 2, and 4 kg.ha-1 treatments in 2014 were 12.3, 23.0, and 37.3 mg.kg-1 (dry weight), respectively. Samples of lateral roots and previous season shoots (with dormant buds) were collected from four trees in each plot on 21 January 2015. Starch abundance was higher in the root organs than that of the shoots and varied between 8.3-18.7 % and 0.26-0.64%, respectively. No significant difference at p<0.05 was found between treatments. Metabolic profiling of over 50 individual compounds indicates alternations in the TCA intermediates and carbohydrates. Elemental analysis (CHNS) on the root and shoots indicate an increasing numerical trend in the C/N ratios in the roots and conversely a decreasing trend in the shoots. Together the data indicate that the application of Zn alters the metabolic profiles and C/N ratios in dormant season shoot and root tissues in pecan.