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3 September 2020 Honey Mesquite Water Relations and Gas Exchange Following Herbicide-Induced Morphological Change
Caitlyn E. Cooper, Tian Zhang, R. James Ansley
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Honey mesquite (Prosopis glandulosa Torr.) may maintain apical dominance after a treatment that causes partial top-kill (PTK) and leaves canopies with “stem flagging.” In contrast, top-killing treatments stimulate multistemmed regrowth (i.e., basal sprouting; BSP). Because this difference may impact competition with grasses, a better understanding of physiology associated with PTK and BSP canopies compared with untreated canopies is needed. We quantified predawn leaf water potential (ΨPD), leaf-level gas exchange rates (photosynthesis [A] and stomatal conductance [gs]), and whole-tree stomatal conductance (Gs) of untreated, PTK, and BSP mesquites 2–11 yr after aerial herbicide application in a north Texas savanna. Total leaf area was nearly 4 × greater in untreated and BSP compared with PTK trees. In a few situations where soil moisture stress was greatest, untreated mesquites exhibited more negative ΨPD and lower leaf-level gas exchange than did PTK mesquites. BSP mesquites occasionally had greater ΨPD and leaf-level gas exchange than untreated mesquites. Since imbalances in root-to-shoot ratios caused by PTK were largely not manifested at the leaf-physiology level, PTK mesquites likely adjusted rapidly to herbicide disturbance. When gs was scaled to the whole canopy, Gs estimates were 3–4 × greater in untreated and BSP than PTK trees. Thus, canopy leaf area was the primary driver of differences in whole-canopy Gs. It is LIKELY that transpiration would be lower in a stand of untreated mesquites compared with PTK mesquites of similar stand density and basal areas before treatment, as results from comparing untreated and PTK mesquites indicate. Partially top-killed trees that maintain apical dominance and do not resprout should compete less with grasses for water and light and facilitate species diversity and heterogeneity.

© 2020 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
Caitlyn E. Cooper, Tian Zhang, and R. James Ansley "Honey Mesquite Water Relations and Gas Exchange Following Herbicide-Induced Morphological Change," Rangeland Ecology and Management 73(5), 673-686, (3 September 2020).
Received: 15 April 2019; Accepted: 3 June 2020; Published: 3 September 2020

Basal sprouting
Partial top-kill
water stress
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