Cunningham, Saul A. , Pullen, Kimberi R. , Colloff, Matthew J. .
Sapflow in Eucalyptus blakelyi halved by insect damage.
Ecohydrological models consider the relationship between tree size and structure (especially leaf area index) and water use, but generally treat herbivory as noise to be ignored. Little is known of how insect damage to leaves influences whole plant water use in trees. Water use is driven by the total leaf area through which transpiration can occur, but the effect of insects are expected be complex. Chewing insects reduce leaf area, whereas sucking and tissue mining insects reduce leaf function without reducing area. Further, plants respond to herbivory in a range of ways, such as altering the rate of leaf production or by abscising leaves. We examined the effect of insects on Eucalyptus blakelyi in woodland near Canberra, Australia, using sapflow velocity as a measure of whole plant water use. We applied insecticide to 16 trees matched to an untreated control group. After 6 months we examined effects on sapflow velocity and various measures of crown condition. Sapflow increased for all trees as they produced leaves over the growing season, but the increase in sapflow for trees without insecticide protection was half that of protected trees. This dramatic effect on sapflow was consistent with effects on crown condition. Unprotected trees had less mass per unit stem in the crown (20% difference). In addition to this effect, unprotected trees had greater loss of leaf functional area from necrosis (17% difference). Notably these effects were detected in a year in which there was not an outbreak of the psyllids (homoptera) that commonly cause severe leaf damage to this tree species. It is predicted that the effect in a psyllid outbreak year would be even more substantial. This result underscores the significant impact that insect herbivores can have on an ecological process of significance to the ecosystem.
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1 - Commonwealth Scientific and Industrial Research Organisation (CSIRO), Entomology, Box 1700, Canberra, ACT, 2601, Australia
Presentation Type: Oral Paper:Papers for Sections
Location: Williford B/Hilton
Date: Tuesday, July 10th, 2007
Time: 11:15 AM