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Abstract: Interactions between roots of Douglas-fir (DF; Pseudotsuga menziesii) seedlings and the laminated root rot fungus Phellinus sulphurascens were investigated using scanning and transmission electron microscopy and immunogold labelling techniques. Scanning electron micrographs revealed that P. sulphurascens hyphae colonize root surfaces and initiate the penetration of root epidermal tissues by developing appressoria within 2d postinoculation (dpi). During early colonization, intra- and intercellular fungal hyphae were detected. They efficiently disintegrate cellular components of the host including cell walls and membranes. P. sulphurascens hyphae penetrate host cell walls by forming narrow hyphal tips and a variety of haustoria-like structures which may play important roles in pathogenic interactions. Ovomucoid–WGA (wheat germ agglutinin) conjugated gold particles (10nm) confirmed the occurrence and location of P. sulphurascens hyphae, while four specific host pathogenesis-related (PR) protein antibodies conjugated with protein A–gold complex (20nm) showed the localization and abundance of these PR proteins in infected root tissues. A thaumatin-like protein and an endochitinase-like protein were both strongly evident and localized in host cell membranes. A DF-PR10 protein was localized in the cell walls and cytoplasm of host cells while an antimicrobial peptide occurred in host cell walls. A close association of some PR proteins with P. sulphurascens hyphae suggests their potential antifungal activities in DF roots. [Copyright &y& Elsevier]

Canadian boreal woodlands and forests cover approximately 3.09 × 106 km2, located within a larger boreal zone characterized by cool summers and long cold winters. Warming since the 1850s, increases in annual mean temperature of at least 2 °C between 2000 and 2050 are highly probable. Annual mean temperatures across the Canadian boreal zone could be 4-5 °C warmer than today's by 2100. All aspects of boreal forest ecosystem function are likely to be affected. Further, several potential 'tipping elements' - where exposure to increasing changes in climate may trigger distinct shifts in ecosystem state - can be identified across the Canadian boreal zone. Approximately 40% of the forested area is underlain by permafrost, some of which is already degrading irreversibly, triggering a process of forest decline and re-establishment lasting several decades, while also releasing significant quantities of greenhouse gases that will amplify the future global warming trend. Warmer temperatures coupled with significant changes in the distribution and timing of annual precipitation are likely to cause serious tree-killing droughts in the west; east of the Great Lakes, however, where precipitation is generally nonlimiting, warming coupled with increasing atmospheric carbon dioxide may stimulate higher forest productivity. Large wildfires, which can cause serious economic losses, are expected to become more frequent, but increases in mean annual area burned will be relatively gradual. The most immediate threats could come from endemic forest insect pests that have the potential for population outbreaks in response to relatively small temperature increases. Quantifying the multiple effects of climate change will be challenging, particularly because there are great uncertainties attached to possible interactions among them, as well as with other land-use pressures. Considerable ingenuity will be needed from forest managers and scientists to address the formidable challenges posed by climate change to boreal ecosystems and develop effective strategies to adapt sustainable forest management practices to the impending changes. [ABSTRACT FROM AUTHOR]