Arboriculture & Urban Forestry 40(2): March 2014 ance. For example, substances such as calcium, often an ingredient of biostimulants, are known to influence changes in cell integrity (Glenn et al. 1988; Marschner 2012) thought to reduce physi- cal damages such as freeze–thaw injury and the osmotic stresses caused by drought and salt dam- age (Raese 1996; Percival and Barnes 2008). Oth- ers promote an increase in overall plant vitality on the premise that a healthy plant is more likely to resist infection than an unhealthy plant (Mar- çais and Bréda 2006). Other studies have shown that biostimulants in the form of marine algae extracts significantly mitigate drought stress (Mancuso et al. 2006; Spann and Little 2010). This study was undertaken to deter- effectiveness mine the of a and salt range MATERIALS AND METHODS Four-year-old containerized trees were of different biostimulants—shown in Table 1— to enhance both drought tolerance. sprayed until runoff using a handheld sprayer with seven commercially available biostimulants (Table 1), ap- plied i) at manufacturers’ recommended rates and ii) double the recommended concentration. Ran- domized block designs assigned the position of the trees and eight trees per treatment were used. Biostimulant enhancement of drought toler- ance commenced on day 10 after applying each biostimulant. Five leaves per tree, ten trees per treatment of evergreen oak (Quercus ilex), rowan (Sorbus aucuparia), and beech (Fagus sylvatica) were detached. Immediately following detach- ment, leaves were dehydrated under labora- Maxicrop Original Resistim Bioplex Fulcrum CRV Redicrop Crop Set Superthrive Active ingredient Seaweed extract Betaine Seaweed + humic acid extract Molasses Seaweed (cytokinin activity) Lactobacillus fermentation product and B5 vitamins Vitimin B and Auxin (NAA) 79 tory conditions by placing abaxial surface down in an uncovered Petri dish, on Whatmans filter paper, and placed in a Merck Environmental Growth Chamber at 21°C for 24 hours at a 35% relative humidity and low light intensity of 15 mmol m-2 s-1 Photosynthetically Active Radia- tion (PAR) to induce stomatal opening and facilitate maximal water loss from leaf tissue (Jensen et al. 1999; Percival and Sheriffs 2002). Biostimulant enhancement of salt toler- ance was assessed using holly (Ilex aquifolium) and evergreen oak. At day 10 aſter biostimulant application, five leaves per tree, 10 trees per bio- stimulant treatment were detached and subjected to sprays of 0% (control), 3%, 6%, 9%, 12% salt (sodium chloride, NaCl) applied until runoff using a handheld sprayer to represent control (0%), minimal (3%), mild (6%), standard (9%), and severe (12%) salt damage. Lethal salt concentra- tions (SC50 (i.e., ) were then calculated at the 50% level the salt concentration required to reduce leaf chlorophyll fluorescence Fv/Fm values as a measure of photosynthetic efficiency by 50%). Chlorophyll Fluorescence Enhancement of drought and/or salinity toler- ance was recorded by measurement of leaf chlo- rophyll fluorescence Fv/Fm values. Fv/Fm is considered a measure of leaf photochemical ef- ficiency (Rosenqvist and van Kooten 2003) that in turn can be used as a non-destructive and rap- id measure of plant vitality and early diagnostic of stress in plants (Meinander et al. 1996). This was achieved by recording values 72 hours post Table 1. Selected biostimulants evaluated to enhance drought and salt tolerance. Product Supplier Maxicrop (UK) Ltd, P.O. Box 6027, Corby, UK Mandops UK Ltd, Eastleigh, Hampshire, UK United Agri Products Ltd, Alconbury Weston, UK Banks Cargill Agriculture Ltd, St Hughs, Lincoln, UK United Agri Products Ltd, Alconbury Weston, UK United Agri Products Ltd, Alconbury Weston, UK Bartlett Tree Research Laboratory, Charlotte, NC, USA ©2014 International Society of Arboriculture
March 2014
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