The distribution of alectorioid lichens in subalpine spruce-fir forests of north-central British Columbia is strongly influenced by vertical position within the canopy; Bryoria dominates upper canopy exposures, while Alectoria dominates lower canopy positions. The hypothesis that this height-related niche partitioning reflects differential growth responses to gradients in canopy microclimate is examined. Field measurements of canopy microclimate, taken over a 2-year period, were used in conjunction with laboratory-based measurements of net photosynthesis (NP) and dark respiration to model net assimilation (NA) response of Alectoria sarmentosa and Bryoria spp. (mixed collections of Bryoria fremontii and B. pseudofuscescens) at two different heights (15 and 4 m) within the canopy. Microclimate measurements indicate that lichen thalli are regularly hydrated from snowmelt events during the winter period (October-April), totalling 26 and 29% of the time, respectively, for Alectoria and Bryoria, though most winter hydration exposure (c. 75%) occurred in the dark. In the summer (May-September), rainfall was the major hydration source, with Alectoria and Bryoria each hydrated c. 16% of the time (45% of this in the dark). The NP temperature optimum (Topt) in light saturated thalli of Alectoria was 18.1 and 22.9°C, for winter and summer measurements, respectively. In Bryoria the corresponding seasonal rise in Topt was smaller, from 15.9 to 16.3°C. Both species showed an increase in maximum rates of NP during the summer period, from 1.52 to 1.92 mg CO2 g−1h−1 for Alectoria, and from 1.79 to 2.33 mg CO2g−1 h−1 for Bryoria. Although lichen hydration events peaked in early winter (October and November), NA modeling predicts that maximum growth should occur during the summer period. In Alectoria, higher rates of NA were predicted for thalli in lower canopy positions, especially during the summer months. In Bryoria, no clear trends of NA uptake with canopy position were observed. Thus, while NP response to gradients of canopy microclimate may provide a basis for niche partitioning in Alectoria, other factors (perhaps exclusionary) may be more important for Bryoria. One such factor is documented, namely the greater sensitivity of Bryoria to extended hydration exposure and we speculate that greater rates of fragmentation in upper canopy exposures may limit upper canopy biomass accumulation in Alectoria. Niche partitioning in these alectorioid lichens may therefore reflect both positive (growth responses) and negative (physical and physiological limitations) responses to gradients in canopy microclimate.

Polysaccharides from thalli of Lasallia pustulata were extracted and characterized. The major fractions were characterized as pustulan, a β-glucan-chitin complex and a β-(1→3)-glucan. Other polysaccharides, which are minor components (less than 5%) solubilized with water from the alkali extracts of thalli, were shown to be galactomannans with a backbone of α-(l→6)- mannose partially substituted at positions 2 by galactofuranose and/or mannopyranose side chains of variable length. The relationship between these polysaccharides and those obtained by the same method from free-living fungi is discussed. The proportion or composition of the different polysaccharides studied was not affected by seasonal environmental conditions over a 2-year period.