Defoliation increases risk of carbon starvation in root systems of mature aspen |
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Authors: | Simon M Landh?usser and Victor J Lieffers |
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Institution: | (1) Department of Renewable Resources, School of Forest Science and Management, University of Alberta, 4-42 Earth Sciences Building, Edmonton, AB, T6G 2E3, Canada |
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Abstract: | Large trees are noted to decline and die over several years after defoliation or extended periods of drought. The underlying
mechanisms of this decline are thought to be driven by moisture limitations to photosynthesis, but alternative considerations
also suggest carbon storage limitations as a driver. This research assesses the non-structural carbohydrate reserves in crowns
and roots tissues during and after defoliation by insects in trembling aspen. We monitored the non-structural carbon reserves
of nine tall mature aspen forest stands over 8 years, including two defoliation events. We report on the carbohydrate dynamics
in root and crown tissues during and after defoliation. Following defoliation, branch reserves recovered to levels of undefoliated
control trees within the same season, while roots took up to 2 years to recover. We argue that in large trees, tissues closest
to the foliage are the first sinks to access C in the phloem stream, while roots, which are more distal and separated by a
long bole, will only receive adequate supplies of C when the other more proximate sinks are sated. These results support the
hypothesis that in times of limited carbon assimilation, root tissues in mature trees experience the longest reduction in
carbon reserves, which likely plays a critical role in tree decline and mortality. |
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