A gall-inducing arthropod drives declines in canopy tree photosynthesis |
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Authors: | Rajit Patankar Sean C Thomas Sandy M Smith |
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Institution: | (1) Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, Canada, M5S 3B2;(2) Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, ON, Canada, M5S 3B3 |
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Abstract: | Mature forest canopies sustain an enormous diversity of herbivorous arthropods; however, with the exception of species that
exhibit large-scale outbreaks, canopy arthropods are thought to have relatively little influence on overall forest productivity.
Diminutive gall-inducing mites (Acari; Eriophyoidae) are ubiquitous in forest canopies and are almost always highly host specific,
but despite their pervasive occurrence, the impacts of these obligate parasites on canopy physiology have not been examined.
We have documented large declines in photosynthetic capacity (approx. 60%) and stomatal conductance (approx. 50%) in canopy
leaves of mature sugar maple (Acer saccharum) trees frequently galled by the maple spindle gall mite Vasates aceriscrumena. Remarkably, such large impacts occurred at very low levels of galling, with the presence of only a few galls (occupying
approx. 1% of leaf area) compromising gas-exchange across the entire leaf. In contrast to these extreme impacts on the leaves
of adult trees, galls had no detectible effect on the gas-exchange of maple saplings, implying large ontogenetic differences
in host tolerance to mite galling. We also found a significant negative correlation between canopy tree radial increment growth
and levels of mite galling. Increased galling levels and higher physiological susceptibility in older canopy trees thus suggest
that gall-inducing mites may be major drivers of “age-dependent” reductions in the physiological performance and growth of
older trees. |
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