Repeated artificial defoliation soon after full leaf expansion, simulating insect damage, reduces xylem hydraulic transport safety in Japanese beech (Fagus crenata Blume)
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Key message
Repeated defoliation soon after full leaf expansion reduces xylem hydraulic transport safety in beech trees.
Abstract
Japanese beech trees undergo branch dieback and eventual mortality following years of repeated leaf loss due to leaf-feeding insects attacking immediately after full leaf expansion. To study the impact of recurrent defoliation on beech debilitation and mortality, we investigated xylem hydraulic transport safety and observed the xylem vessel architecture in field-grown medium-sized Japanese beech trees that had been artificially defoliated repeatedly for 4 years immediately after full leaf expansion. Multiple years of defoliation immediately after full leaf expansion increased the susceptibility to xylem cavitation (P50 value; − 4.46 ± 0.38 MPa (mean ± SD) for non-defoliated control beeches, and − 2.32 ± 0.20 MPa for defoliated beeches), despite a decrease in their vessel diameter and an increase in their vessel density. In defoliated beech, many irregularly shaped, axially wrinkled and partially cracked vessels, mountain-folded intervessel pits, and fibers with thin and less-lignified cell walls were observed. The intervessel double-wall thickness of the defoliated beech was thinner than that of the control beech. Furthermore, the size and shape of intervessel pits did not change in defoliated beech, but the density of intervessel pits and the total number and total area of intervessel pits per 1 mm of vessel length increased. We conclude that the increased susceptibility to xylem cavitation caused by repeated defoliation immediately after full leaf expansion may be due to an increased total area of intervessel pits with thin pit membranes per unit vessel wall area, in addition to cell wall alteration and vessel deformation and damage.
期刊介绍：
Trees - Structure and Function publishes original articles on the physiology, biochemistry, functional anatomy, structure and ecology of trees and other woody plants. Also presented are articles concerned with pathology and technological problems, when they contribute to the basic understanding of structure and function of trees. In addition to original articles and short communications, the journal publishes reviews on selected topics concerning the structure and function of trees.
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