Circadian rhythms and leaf characteristics of subalpine Eucalyptus pauciflora: The effects of environmental exposure on photosynthetic machinery

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Christine Mauger
Julia Hammer
Chen Liang
Cameron McArthur
Angela Stoddard




This study explored whether snow gums (Eucalyptus pauciflora) in a subalpine region use circadian rhythms for photosynthesis and whether age and exposure affect photosynthetic machinery. Fv/Fm, SPAD and specific leaf area (SLA) were measured in individual leaves to assess variation in leaf traits. Fv/Fm was not significantly different between exposed and sheltered trees, but old leaves had significantly higher Fv/Fm values than young leaves. SPAD was higher in exposed trees and old leaves had significantly higher chlorophyll content. SLA was significantly lower in old leaves, and sheltered leaves had significantly higher SLA than exposed leaves. Increase in SLA with exposure was greater in young leaves. Branches from sheltered and exposed E. pauciflora were harvested then placed in light and dark treatments. Stomatal conductance was tested at various times to determine if leaf stomata were opening without access to sunlight. At the time of this experiment, there had been no previous known studies on circadian rhythms in E. pauciflora. Conductance rates were higher in the light treatment, and across this treatment it was higher at 11 am than at night. There was no effect of exposure on conductance rates in the light treatment. In the dark treatment, exposed leaves had lower conductance rates than sheltered leaves. For sheltered and exposed leaves, conductance was greater at dawn than at 11 pm and greater again at 11 am than at dawn, suggesting E. pauciflora do use circadian rhythms for photosynthesis.

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