University Of Tasmania

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Interactive effects of water supply and defoliation on photosynthesis, plant water status and growth of Eucalyptus globulus Labill

journal contribution
posted on 2023-05-17, 04:36 authored by Quentin, AG, Anthony O'GradyAnthony O'Grady, Christopher BeadleChristopher Beadle, Caroline MohammedCaroline Mohammed, Pinkard, EA
Increased climatic variability, including extended periods of drought stress, may compromise on the health of forest ecosystems. The effects of defoliating pests on plantations may also impact on forest productivity. Interactions between climate signals and pest activity are poorly understood. In this study, we examined the combined effects of reduced water availability and defoliation on maximum photosynthetic rate (Asat), stomatal conductance (gs), plant water status and growth of Eucalyptus globulus Labill. Field-grown plants were subjected to two water-availability regimes, rain-fed (W−) and irrigated (W+). In the summer of the second year of growth, leaves from 75% of crown length removed from trees in both watering treatments and physiological responses within the canopies were examined. We hypothesized that defoliation would result in improved plant water status providing a mechanistic insight into leaf- and canopy-scale gas-exchange responses. Defoliated trees in the W+ treatment exhibited higher Asat and gs compared with non-defoliated trees, but these responses were not observed in the W− treatment. In contrast, at the whole-plant scale, maximum rates of transpiration (Emax) and canopy conductance (GCmax) and soil-to-leaf hydraulic conductance (KP) increased in both treatments following defoliation. As a result, plant water status was unaffected by defoliation and trees in the defoliated treatments exhibited homeostasis in this respect. Whole-plant soil-to-leaf hydraulic conductance was strongly correlated with leaf scale gs and Asat following the defoliation, providing a mechanistic insight into compensatory up-regulation of photosynthesis. Above-ground height and diameter growth were unaffected by defoliation in both water availability treatments, suggesting that plants use a range of responses to compensate for the impacts of defoliation.


Publication title

Tree Physiology










Tasmanian Institute of Agriculture (TIA)


Oxford University Press

Place of publication

United Kingdom

Rights statement

Copyright 2012 The Authors.

Repository Status

  • Restricted

Socio-economic Objectives

Forestry not elsewhere classified