Arthur L. Fredeen

Effects of phosphorus nutrition on photosynthesis in Glycine max (L.) Merr.

The effects of phosphorus nutrition on various aspects of photosynthetic metabolism have been examined for soybean plants (Glycine max) grown in growth chambers. Orthophosphate was supplied at two levels in 0.5-strength Hoaglands solution. At the end of the 19-d growth period, plants grown at 10 μM KH2PO4 (low-P plants) had undergone a 40% drop in net CO2 exchange (averaged over a 16-h light period), as compared with control plants grown with 200 μM KH2PO4. Low-P resulted in reductions in the initial activities of five, and in the total activities of seven, Calvin-cycle enzymes. Notable exceptions were the initial and total activities of chloroplastic fructose-1,6-bisphosphatase (EC 3.1.3.11) which were increased by 85 and 53%, respectively, by low-P. Low-P decreased leaf 3-phosphoglycerate (PGA) levels most (by 80%), ribulose-1,5-bis-phosphate (RuBP) less (by 47%) while triose-phosphate (TP) was not significantly changed. The results indicate that photosynthetic CO2-fixation in low-P plants was limited more by RuBP regeneration than by ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) activity. Ribulose-1,5-bisphosphate regeneration in low-P plants did not appear to be limited by ATP and-or NADPH supply because ATP/ADP and NADPH/ NADP+ ratios were increased by 60 and 37%, respectively, by low-P, and because TP/PGA ratios were higher in low-P plants. Low-P may diminish RuBP regeneration, and hence photosynthesis, by reducing Calvin-cycle enzyme activity, in particular, the initial activity of ribulose-5-phosphate kinase (EC 2.7.1.19) (44% reduction), and by enhancing the flux of carbon into starch biosynthesis.

The influence of overstorey Populus on epiphytic lichens in subboreal spruce forests of British Columbia

The composition and abundance of lichen communities on conifer saplings beneath five overstorey tree species were compared at three subboreal forest site types in east-central British Columbia. Site-level differences in lichen communities were attributed to different levels of moisture and light limitations in the understorey. At sites with adequate moisture and light, cyanolichens were uniformly abundant and species rich on conifer saplings beneath different understorey species. However, at sites with moisture or light limitations, cyanolichens were more abundant and species rich on conifer saplings beneath overstorey Populus than on saplings beneath other overstorey tree species. Cyanolichen communities also showed greater species richness on conifer saplings beneath the Populus canopy than on the trunk of Populus itself. Differences in calcium, phosphorus, molybdenum, and manganese availability in throughfall precipitation failed to explain much of the variation in lichen community structure. These res...

Contrasting Arboreal and Terrestrial Macrolichen and Bryophyte Communities in Old-Growth Sub-Boreal Spruce Forests of Central British Columbia

Abstract Macroclichen and bryophyte species diversity, abundance, biomass and nitrogen stocks were compared between arboreal and terrestrial habitats in old-growth sub-boreal spruce forests in central British Columbia, Canada on the two most common soil types in the area, fine- and coarse-textured soils. A total of 118 macrolichen and bryophyte species were identified, including 71 species of macrolichens (44 arboreal and 43 terrestrial) and 47 species of bryophytes, of which only one moss (Orthotrichum sp.) was arboreal. Macrolichen functional groups varied in both diversity and abundance between arboreal and terrestrial communities. Cyanolichens were common in both arboreal and terrestrial habitats, but were much more abundant arboreally than terrestrially. This epiphytic biomass was largely attributed to the tripartite cyanolichen species, Lobaria pulmonaria, while the most common terrestrial macrolichens were bipartite Peltigera cyanolichen species. From a biomass perspective, the epiphyte community was almost entirely lichens while the terrestrial community was predominantly bryophytes. Terrestrial and arboreal macrolichens and bryophytes made a relatively small contribution to total forest above-ground biomass (0.5–1.4% or 1698–3339 kg ha−1), however, a comparison between macrolichen and bryophyte biomass and tree foliar biomass showed lichens and bryophytes to be equivalent to 11.7–20.5% of tree foliar biomass. Macrolichens made a proportionately large contribution when compared to forest foliar nitrogen and contained 6.4–8.1% of forest foliar nitrogen. Nitrogen contents varied greatly between functional groups, from a maximum of 3.98% N in terrestrial bipartite cyanolichens to a minimum of 0.37% N in Alectoria hair lichens. In total, terrestrial and arboreal lichens and bryophytes represented 20–39 kg N ha−1 in this old-growth sub-boreal spruce ecosystem.