Browsing by Author "Vargas, Ana I."

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    Pruning after flooding hastens recovery of flood-stressed avocado (Persea americana Mill.) trees
    (2014) Sanclemente, Maria Angelica; Schaffer, Bruce; Gil, Pilar M.; Vargas, Ana I.; Davies, Frederick S.
    Two experiments (Expts. 1 and 2) were conducted at different times with avocado (Persea americana Mill. cv. Choquette) trees in containers to test the effects of leaf pruning immediately after removing trees from short-term flooding on tree recovery. Trees in each experiment were divided into two flooding treatments: (1) flooded, or (2) non-flooded. Trees in each flooding treatment were divided into two pruning treatments: (1) pruned; approximately two-thirds of the canopy removed by pruning immediately after trees were removed from flooding (unflooded), or (2) non-pruned. In each experiment, net CO2 assimilation (A), stomatal conductance of water vapor (g(s)), transpiration (a water use efficiency (WUE, calculated as A/E) and xylem sap flow (in Expt. 2) were determined daily during the flooding period and periodically after trees were unflooded until harvest time in each flooding/pruning treatment. Tissue dry weights were determined for trees in all treatments at the end of the experiment (several weeks after trees were unflooded). Net CO2 assimilation, g(s), E and WUE of flooded trees decreased after 2 and 5 days and trees were unflooded after 3 and 6 days in Expts. 1 and 2, respectively. After trees were unflooded, A, g(s), E and WUE were lower in flooded trees than in non-flooded trees for a few weeks, but these reductions were greater for pruned than non-pruned trees. Eventually, A, g(s), E and WUE of flooded trees in both the pruned and non-pruned treatments returned to values similar to those of non-flooded trees. After trees were unflooded, for trees in the pruned treatment, xylem sap flow was generally not significantly affected by flooding. However, for non-pruned trees, xylem sap flow was usually lower in the flooded than non-flooded trees. In each experiment, leaf dry weight and total plant dry weight were significantly lower for flooded than non-flooded trees only in the non-pruned treatments. In Expt. 2, root and stem dry weights were also lower in flooded than non-flooded trees only in the non-pruned treatment. The results indicate that pruning the canopy of avocado immediately after trees are removed from short-term flooding hastens plant recovery. It is postulated that the hastened recovery was due to pruning bringing the shoot to root ratio of flooded trees (with damaged roots) and the subsequent supply and demand for water and nutrients into better equilibrium in flooded trees, allowing pruned trees to recover more quickly from flooding compared to non-pruned trees. (C) 2014 Elsevier B.V. All rights reserved.
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    Stem electrical potential variations may aid in the early detection of drought stress in fruit-bearing trees
    (2023) Gil, Pilar M.; Vargas, Ana I.
    P. M. Gil and A.I. Vargas. 2023. Stem electrical potential variations may aid in the early detection of drought stress in fruit-bearing trees. Int. J. Agric. Nat. Resour. 116-129. Electrical plant signaling as a variation potential (VP) occurs in response to a wide range of stimuli, and it is associated with the induction of sudden changes in xylem pressure. Additionally, there is evidence that electrical potential (EP) of plants changes with changing soil water content. Therefore, the use of EP as a direct plant measurement of plant water status may have potential as water stress monitoring information. EP measurements within plant stems indirectly correlate with sap flow (SF), which is one possible variable for estimating plant water use. However, whether this relationship is stable under drought conditions is not known. The present work investigated the relationships between SF and EP variations during an 18-day drought period on three avocado trees to test the hypothesis that the relationships between SF and EP may be lost due to drought intensity. The results showed that short-term variations in EP were positively associated with vapor pressure deficit (VPD) and SF variations but negatively associated with soil water content (SWC). An increase in VP emissions was observed as drought advanced, which was negatively associated with stem water potential (SWP). After 18 days of drought, irrigation almost completely suppressed short-term variations in EP. The present work provides preliminary results that strongly suggest a relationship between drought stress and EP variations in plant stems. Further research is needed to confirm whether the EP trends observed during drought are due to cavitation events and emission of VP signals and/or linked to other physiological processes, e.g., pH changes in response to drought or embolism. Meanwhile, the present work indicates that short-term variations in EP (dEP) are strongly associated with the intensity of drought stress, thus stem electrical potential variations may aid in the early detection of drought stress in fruit-bearing trees.