Respiration in lodgepole pine parasitized by American dwarf mistletoe

Abstract

Rates of dark respiration were determined for foliated twig tips of branches from Pinuscontorta and for aerial shoots of Arceuthobiumamericanum. Tree samples were obtained from twigs of branches on uninfected trees, twigs from uninfected branches on infected trees, and from uninfected twigs of branches having localized infections. Rates of dark respiration were significantly lower for twigs from infected trees as compared with twigs from uninfected trees. The rate of dark respiration for aerial shoots of A. americanum was significantly higher than the host samples. The biomass of plant parts from infected and uninfected P. contorta was measured. We found that the ratio of relative bole to branch mass changed from 3.8:1 for lightly infected trees to 1.6:1 for heavily infected trees. This apparent shift in mass allocation from stem to branch wood would account for a portion of the reduction in timber volume that is associated with infection by Arceuthobium.

Dwarf mistletoe affects whole-tree water relations of Douglas fir and western larch primarily through changes in leaf to sapwood ratios

“…Changes in biomass allocation caused by dwarf mistletoe are likely to upset allocational balances to the detriment of hosts independently of parasitic effects. Specifically, previous studies (Tinnin and Knutson 1980;Broshot et al 1986;Wanner and Tinnin 1986) suggest that dwarf mistletoe may increase total tree leaf area to sapwood cross sectional area ratios (A L :A S ). The potential consequences of higher A L :A S ratios in infected trees include increased demand of water relative to supply, and therefore, increased susceptibility to drought stress.…”

“…These parasitic plants directly divert resources from their hosts (Hull and Leonard 1964;Miller and Tocher 1975;Schulze and Ehleringer 1984;Marshall and Ehleringer 1990;Rey et al 1992;Marshall et al 1994) and may induce host physiological responses that result in abnormal growth patterns and altered resource allocation (Tinnin and Knutson 1980;Livingston et al 1984;Broshot et al 1986;Wanner and Tinnin 1986). Previous work on mistletoes has focused on the parasitic nature of the mistletoe and the relative physiological performance of mistletoes and their hosts (Fisher 1983;Glatzel 1983;Hollinger 1983;Ehleringer et al 1986;Goldstein et al 1989;Marshall and Ehleringer 1990;Rey et al 1992).…”

“…It is one of the most important disease agents in natural and commercial North American coniferous forests, with severe consequences for tree structure, health, reproductive output, and ultimately on forest productivity (Hawksworth and Wiens 1972;Piirto et al 1974;Hawksworth 1978;Parmeter 1978;Filip 1984;Thompson et al 1984;Filip and Parks 1987;Mathiasen and Hawksworth 1988;Trummer et al 1998). Dwarf mistletoes cause dramatic changes in host biomass allocation which may have large effects on the health of their hosts in addition to the direct parasitic effects of the mistletoes (Tinnin and Knutson 1980;Livingston et al 1984;Broshot et al 1986;Wanner and Tinnin 1986;Hawksworth and Wiens 1996). Furthermore, understanding the consequences of parasiteinduced changes in host biomass allocation may be particularly important to fully comprehend how mistletoes affect their hosts because dwarf mistletoes' slow growth and reduced size may not constitute a strong resource sink to their hosts.…”

Effects of Dwarf Mistletoe on Climate Response of Mature Ponderosa Pine Trees

“…Several studies have demonstrated that transpiration rates of dwarf mistletoe shoots are higher than those of host tissues, which may increase both water stress in the host and allocation of resources to mistletoe shoots (Fisher 1983;Tocher et al 1984;Wilson and Calvin 1996). Additional evidence indicates that infection increases needle surface area while decreasing volume (Tinnin and Knutson 1980;Wanner and Tinnin 1986). Such shifts in the distribution of biomass in the host crown could lower water-use efficiency, resulting in lower tolerance to drought stress (Sala et al 2001).…”

Effects of <em>Arceuthobium americanum</em> on twig growth of <em>Pinus contorts</em>.

“…In addition to the significant changes in branch structure that result from the infection of P. contorta by A. americanum, it is known that the starch content of needles increases (Broshot and Tinnin 1986), respiratory rates decrease (Wanner and Tinnin 1986), and patterns of carbon allocation change (Leonard and Hull 1965). The many changes in structure and function that occur after infection are at least related to, if not part of, the mechanisms that cause host decline.…”