Soil-application of Zinc-EDTA Increases Leaf Photosynthesis of Immature ‘Wichita’ Pecan Trees

Abstract

<jats:p>Zinc deficiency is common in pecan (<jats:italic>Carya illinoinensis</jats:italic>) grown in alkaline, calcareous soils. Zinc (Zn)-deficient pecan leaves exhibit interveinal chlorosis, decreased leaf thickness, and reduced photosynthetic capacity. Low photosynthesis (P<jats:sub>n</jats:sub>) contributes to restricted vegetative growth, flowering, and fruiting of Zn-deficient pecan trees. Our objectives were to measure effects of soil-applied ethylenediaminetetraacetic acid (EDTA)-chelated Zn fertilizer on gas exchange of immature ‘Wichita’ pecan and characterize the relationship between leaf Zn concentration and P<jats:sub>n</jats:sub>. The study orchard had alkaline and calcareous soils and was planted in Spring 2011. Zinc was applied throughout each growing season as Zn EDTA through microsprinklers at rates of 0 (Control), 2.2, or 4.4 kg·ha<jats:sup>−1</jats:sup> Zn. Leaf gas exchange and SPAD were measured on one occasion in the 2012 growing season, four in 2013, and five in 2014. Soil Zn-EDTA applications significantly increased the leaf tissue Zn concentration throughout the study. On all measurement occasions, net P<jats:sub>n</jats:sub> was significantly increased by soil-applied Zn EDTA compared with the control, but P<jats:sub>n</jats:sub> was not different between the two soil-applied Zn-EDTA treatments. Leaf P<jats:sub>n</jats:sub> in midseason did not increase at leaf tissue Zn concentrations above 14–22 mg·kg<jats:sup>−1</jats:sup>. Leaf SPAD consistently followed a similar pattern to P<jats:sub>n</jats:sub>. Soil Zn-EDTA application increased leaf stomatal conductance (<jats:italic>g</jats:italic><jats:sub>S</jats:sub>) compared with the Control early through midseason but not after August. Intercellular CO<jats:sub>2</jats:sub> concentration was significantly lower for Zn-EDTA-treated trees than the Control even on dates when there was no significant difference in <jats:italic>g</jats:italic><jats:sub>s</jats:sub>, which suggests that soil application of Zn-EDTA alleviated nonstomatal limitations to P<jats:sub>n</jats:sub> caused by Zn deficiency.</jats:p>

Leaf Net Photosynthesis, Leaf Greenness, and Shoot Lignin Content of Nonbearing Pecan Trees at Two Nitrogen and Nickel Application Rates

“…Pecan leaf greenness and P n activity are affected by leaf tissue concentrations of N and micronutrients. Heerema et al (2017) found that zinc (Zn) application via fertiga-tion increased P n on immature pecan trees. Sherman et al (2017) observed an improvement in P n under foliar applications of manganese (Mn) on nonbearing pecan trees.…”

Nutraceutical Properties of Pecan Kernels Are Affected by Soil Zinc Fertilizer Application

“…Along with its importance for plant growth and development (Broadley et al, 2012), Zn has been noted to have a critical role in defense against reactive oxygen species (Cakmak, 2000). In pecan, Zn fertilizer application and higher leaf tissue Zn concentrations up to 14-22 mg • kg -1 (by dry weight) are associated with increasing chlorophyll content and photosynthesis rate (Heerema et al, 2017;Hu and Sparks, 1991), which would likely support the biosynthesis of antioxidants and an increase in antioxidant activity. Studies have shown that foliar or soil application of Zn improved the total phenolic content and increased the antioxidant enzyme activity in other crop species, including wheat (Triticum aestivum; Ma et al, 2017), grape (Vitis vinifera; Song et al, 2015), and pistachio (Tavallali et al, 2010).…”

“…Zinc availability for root uptake is limited due to reactions with soil carbonates and hydroxyl groups in alkaline, calcareous soils resulting in deficiencies that commonly negatively impact an orchard's tree health, fruit production, and commercial performance (Udo et al, 1970;Walworth and Heerema, 2015;. Zinc deficiency symptoms in pecan characteristically include shortened internodes (''rosette''), severely reduced leaf area, thinner leaves, wavy leaf margins, interveinal leaf chlorosis and necrosis, and shoot terminal dieback (Alben et al, 1932;Heerema, 2013;Heerema et al, 2017;Hu and Sparks, 1991;Ojeda-Barrios et al, 2012). In immature orchards, pecan tree growth and establishment rates are negatively affected by Zn deficiency (Walworth et al, 2017) and in mature orchards, Zn deficiency reduces pistillate flower production, fruit set, individual nut weight, and percent kernel weight (Hu and Sparks, 1990).…”

“…Zinc acquired by pecan trees through root uptake is distributed more widely in the plant tissues than Zn acquired from foliar fertilizer sprays (Wadsworth, 1970;Walworth et al, 2017) and is therefore expected to impact tree physiology in different ways. Although soil applied Zn EDTA can eliminate Zn deficiency symptoms, orchards managed exclusively by soil Zn fertilizer application usually have lower leaf tissue Zn concentrations than comparable orchards managed with foliar Zn sprays, and it therefore has recently been proposed that leaf tissue critical levels for Zn should be lower for pecan orchards managed with soil applied Zn EDTA than for those managed with foliar sprays (i.e., 30 mg • kg -1 for soil applied Zn EDTA vs. 50 mg • kg -1 for foliar applied Zn) (Heerema et al, 2017;Walworth and Heerema, 2019;Walworth et al, 2017).…”

Changes in nutrient concentration and oxidative metabolism in pecan leaflets at different doses of zinc

“…Zinc is a critical element that is required in large quantities for vegetative growth, shoot elongation and quality nut (Huang et al 2019). In this sense, the supply of Zn 2+ is mainly carried out via foliar and on production trees (Heerema et al 2017). Its application has been observed to modify the concentration of nutrients, yield and quality of the harvested nut (Ojeda-Barrios et al 2014); however, the behavior has been inconsistent due to the soil conditions (pH and high carbonate content) and cultivar of pecan tree used (Huang et al 2019).…”