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


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Eyles, A, Smith, D, Pinkard, EA, Smith, I, Corkrey, R, Elms, S, Beadle, CL and Mohammed, CL 2011 , 'Photosynthetic responses of field-grown Pinus radiata trees to artificial and aphid-induced defoliation' , Tree Physiology, vol. 31 , pp. 592-603 , doi: 10.1093/treephys/tpr046.

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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
Authors/Creators:Eyles, A and Smith, D and Pinkard, EA and Smith, I and Corkrey, R and Elms, S and Beadle, CL and Mohammed, CL
Keywords: defoliation, Essigella californica, herbivory, insect pest, net CO2 assimilation.
Journal or Publication Title: Tree Physiology
ISSN: 0829-318X
DOI / ID Number: 10.1093/treephys/tpr046
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Copyright © 2011 Oxford University Press

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