© 2006 Heron Publishing—Victoria, Canada
Impact of eastern dwarf mistletoe (Arceuthobium pusillum) infection on the needles of red spruce (Picea rubens) and white spruce (Picea glauca): oxygen exchange, morphology and composition
Jaret S. Reblin (1, 3), Barry A. Logan (1) and David T. Tissue (2)
1. Department of Biology, Bowdoin College, Brunswick, ME 04011, USA / 2. Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409-3131, USA / 3. Corresponding author (jreblin@bowdoin.edu) / Received August 31, 2005; accepted December 22, 2005; published online June 30, 2006
Summary
Eastern dwarf mistletoe (Arceuthobium pusillum Peck) is a hemiparasitic angiosperm that infects white spruce (Picea glauca (Moench) Voss) and red spruce (P. rubens Sarg.) in northeastern North America. The effects of mistletoe infection differ substantially between white and red spruce,
with white spruce suffering greater infection-induced mortality. In the present study, we sought to determine the role that
species-specific differences in needle-scale responses to parasitism may play in the observed differences in the effect of
infection on host tree health. Based on the measurements made, the most apparent effect of parasitism was a reduction in needle
size distal to infections. The magnitude of this reduction was greater in white spruce than in red spruce. Eastern dwarf mistletoe
was a sink for host photosynthate in red spruce and white spruce; however, there were no adjustments in needle photosynthetic
capacities in either host to accommodate the added sink demands of the parasite. Needle total nonstructural carbohydrate concentrations
(TNC) were also unaltered by infection. Red spruce needles had higher TNC concentrations despite having lower overall photosynthetic
capacities, suggesting that red spruce may be more sink limited and therefore better able to satisfy the added sink demands
of parasitic infection. However, if carbon availability limits the growth of the mistletoe, one may expect that the extent
of the parasitic infection would be greater in red spruce. Yet in the field, the extent of infection is generally greater
in white spruce. Taken together, these results suggest that dwarf mistletoe may not substantially perturb the carbon balance
of either host spruce species and that species-specific differences in needle-scale responses to the parasite cannot explain
the contrasting effects of infection on white spruce and red spruce.
Keywords:
mistletoe–host interaction, nitrogen nutrition, parasitic angiosperm, source–sink balance.
