A phytocentric perspective of Asterolecanium quercicola Bouché infestation on Quercus robur L. trees along an urbanization gradient
Year: 1997
Type: article
Abstract: Diurnal courses in gas exchange, photochemical efficiency and water relations were monitored during two late summers in three groups of adult Quercus robur L. trees, planted along an urbanization gradient that correlated positively with the degree of die-back exhibited by the trees. Leaf carbon:nitrogen ratios, proline and polyphenol levels were monitored to explain why the intermediate group of trees were more severely infested (p ≤ 0.01) with Asterolecanium quercicola (Bouché). All three groups of trees showed a significant correlation of net photosynthesis with photon flux density (PPFD), but A correlated more positively with the pre-dawn leaf water potential ψpd of the moderately (trees of group b, i.e. at the edge of town) and severely (trees of group c, i.e. urban) water-stressed trees. A of the rural trees and stomatal conductance (g) of the three groups of trees showed little correlation ψpd values. Possibly due to the long-term effect of stress, g, as reflected by changes in the transpiration rate (E), showed a significantly (p ≤ 0.01) higher sensitivity to relative ambient humidity (RH) in the trees of groups b and c. Photochemically, a close coupling was found to exist between A, ψpd, RH, the time needed to reach the maximum fluorescence level, i.e. FTm, and S, i.e. the complementary area normalized to the variable fluorescence, indicating that the trees were also affected at this level of organization. Proline accumulation occurred in the trees of group c but not in the trees of group b, as opposed to the polyphenolic concentrations which were significantly (p ≤ 0.05) higher in the trees of group b than in the trees of group c. A possible explanation for the higher infestation of A. quercicola on the trees in group b is given in terms of their host specificity and changes in these trees' nitrogen levels.
Source: South African Journal of Botany
Authors: L. van Rensburg, G.H.J. Krüger, B. Ubbink, M.C. Scholes, J. Peacock
Institutions: North-West University, University of the Witwatersrand
Language: English
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $2,750
OpenAlex ID: W2268220068