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Photosynthetic responses of field-grown Pinus radiata trees to artificial and aphid-induced defoliation

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Eyles, A and Smith, D and Pinkard, EA and Smith, I and Corkrey, R and Elms, S and Beadle, CL and Mohammed, CL (2011) Photosynthetic responses of field-grown Pinus radiata trees to artificial and aphid-induced defoliation. Tree Physiology, 31. pp. 592-603. ISSN 0829-318X

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Abstract

The phloem-feeding aphid Essigella californica represents a potential threat to the productivity of Pinus radiata plantations in south-eastern Australia. Five- and nine-year-old field trials were used to characterize the effects of artificial and natural aphid-induced (E. californica) defoliation, respectively, on shoot photosynthesis and growth. Photosynthetic capacity (Amax) was significantly greater following a 25% (D25) (13.8 μmol m−2 s−1) and a 50% (D50) (15.9 μmol m−2 s−1) single-event uppercrown artificial defoliation, 3 weeks after defoliation than in undefoliated control trees (12.9 μmol m−2 s−1). This response was consistently observed for up to 11 weeks after the defoliation event; by Week 16, there was no difference in Amax between control and defoliated trees. In the D50 treatment, this increased Amax was not sufficient to fully compensate for the foliage loss as evidenced by the reduced diameter increment (by 15%) in defoliated trees 36 weeks after defoliation. In contrast, diameter increment of trees in the D25 treatment was unaffected by defoliation. The Amax of trees experiencing upper-crown defoliation by natural and repeated E. californica infestations varied, depending on host genotype. Despite clear differences in defoliation levels between resistant and susceptible genotypes (17 vs. 35% of tree crown defoliated, respectively), growth of susceptible genotypes was not significantly different from that of resistant genotypes. The observed increases in Amax in the lower crown of the canopy following attack suggested that susceptible genotypes were able to partly compensate for the loss of foliage by compensatory photosynthesis. The capacity of P. radiata to regulate photosynthesis in response to natural aphid-induced defoliation provides evidence that the impact of E. californica attack on stem growth will be less than expected, at least for up to 35% defoliation.

Item Type: Article
Keywords: defoliation, Essigella californica, herbivory, insect pest, net CO2 assimilation.
Journal or Publication Title: Tree Physiology
Page Range: pp. 592-603
ISSN: 0829-318X
Identification Number - DOI: 10.1093/treephys/tpr046
Additional Information: Copyright © 2011 Oxford University Press
Date Deposited: 23 Feb 2012 02:39
Last Modified: 23 Feb 2012 02:39
URI: http://eprints.utas.edu.au/id/eprint/12674
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