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Growth and physiological responses of Eucalyptus Globulus Labilladiere following defoliation
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Abstract
Many defoliating herbivores cause damages to Eucalyptus globulus Labill.
plantations, reducing the quality and value of the wood products they source. This
damage ranges from mild to severe removal of leaf surface, and can result in
significant reductions in yield. Our knowledge of physiological responses to
defoliation in this species is incomplete, with previous studies focusing on very young
trees and ignoring the potential interaction of abiotic stress with defoliation.
Projections of future climates in many of the eucalypt-growing parts of the world
suggest that abiotic stress, particularly degree of water stress will increase. In
addition, there is strong evidence that changing climate, and particularly increasing
temperature, is likely to favour many of the defoliating pests commonly associated
with E. globulus.
The objectives of work described in this thesis were to investigate the physiological
strategies adopted by E. globulus in response to a defoliation event, determine their
effects on growth and water relations, and examine the interaction with limited water
supply, with the aim of improving our capacity to predict the impact of defoliation on
tree productivity and water use.
The main studies investigating tree responses to defoliation have utilised artificial
defoliation treatments rather than natural defoliation because of logistical constraints.
Although artificial manipulations are assumed to have significant advantages, the
adequacy of the artificial method has been questioned in term of accuracy and
differences in the plant responses. I tested that E. globulus respond differently to both
artificial and natural defoliations. The results showed that the directions of response to
artificial and insect defoliation were very similar. However, the influence of
differential magnitude of the responses was more difficult to ascertain. I conclude that
artificial defoliation may not accurately reflect the full strength of effects from insect
defoliation, and caution must be exercised in extrapolating results of simulated
herbivory experiments.
Most previous studies of E. globulus responses to defoliation have focused on young,
pre-canopy closure trees, and none have examined physiological responses of older
trees to defoliation. Substantial defoliation can occur post-canopy closure. The effects
of a single defoliation event on 4-year-old E. globulus were investigated on growth,
photosynthetic and water relation responses in non-limited water supply conditions.
The trees responded to removal of 45% of leaf area by a transient change in stem
growth, change in crown architecture, the up-regulation of photosynthesis likely via
the improvement of tree water status. It was concluded that 4-year-old E. globulus
were able to compensate for the loss of foliage.
Plantations of E. globulus are being established increasingly on lower rainfall sites,
and in addition drought conditions are projected to increase in many areas of Australia
over the next century. There is little understanding of the interactions of water stress
and defoliation, although some results suggest that defoliation may be beneficial to
trees growing under water limitation. I tested the hypothesis that partial defoliation
would alleviate the effects of water stress. The effect leaf removal on 75% of crown
length of 1-year-old E. globulus on growth, gas exchange and water use was
examined in irrigated and rain-fed plots. Over a short-term period, trees responded to
the interaction of limited water supply and defoliation by maintaining tree growth,
increasing tree transpiration rate per unit leaf area, canopy conductance and hydraulic
conductance, while maintaining the gradient of leaf water potential constant. It was
concluded that defoliated trees were able to ease the effect of water stress by
improving plant water status. Also, the findings were meeting the requirements of the
theoretical hydraulic model.
| Item Type: | Thesis - PhD |
|---|---|
| Authors/Creators: | Quentin, AG |
| Copyright Holders: | The Author |
| Copyright Information: | Copyright 2010 the author |
| Additional Information: | Manuscript 1 identified as embedded in the thesis (Quentin, A.G. Physiological approach of insect defoliation in evergreen trees. International Forest Review, in preparation.) does not appear to have been published. Chapter 3 appears to be the equivalent of a pre or post print article. Quentin, A.G., Pinkard, E.A., Beadle C.L., Wardlaw, T.J., O'Grady, A.P., Paterson S. and Mohammed C.L. (2010) Do artificial and natural defoliation have similar effects on physiology of Eucalyptus globulus Labill. seedlings? Annals of Forest Science, 67: 203-211. The final publication is available at Springer via http://dx.doi.org/0.1051/forest/2009096 Manuscript 3 identified as embedded in the thesis (Quentin, A.G., Pinkard, E.A., Beadle C.L. and O'Grady, A.P. (2010) Effects of partial defoliation on closed canopy Eucalyptus globulus Labill.: Growth, biomass allocation and carbohydrates. Forest, Ecology and Management, 261(3), 695-702) does not appear in similar words to the published article. Manuscript 4 identified as embedded in the thesis (Quentin, A.G, Beadle C.L., O'Grady, A.P., Pinkard, E.A. and Mohammed Manuscript 5 identified as embedded in the thesis (Quentin, A.G., O'Grady, A.P., Beadle C.L., Worledge, D. and Pinkard, E.A. Manuscript 6 identified as embedded in the thesis appears to be a pre-copyedited, author-produced PDF of an article accepted for publication in Tree physiology following peer review. The version of record Quentin, A.G, Beadle C.L., O'Grady, A.P., Pinkard, E.A. and Mohammed C.L. (2010) Interactive effects of water supply and defoliation on Eucalyptus globulus photosynthesis, plant water status and growth, Tree Physiology, 2012, 32(8), 958-967 is available online at: http://dx.doi.org/10.1093/treephys/tps066 |
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