Cover illustration: (Top) An arbuscular mycorrhizal fungus (UY 110) stained pink with acid fuchsin: proliferating hyphae in a decaying patch of organic matter in soil. Photograph by A Hodge (University of York, UK) and M Firestone (University of California, USA). (Upper middle) Roots of Hakea prostata R. Br., a Western Australian Proteacean, adapted to extremely nutrient-impoverished soils. Formation and functioning of specialized ‘cluster roots’ is highly ‘plastic’: stimulated by extremely low phosphorous concentration in the root environment and suppressed at supra-optimal levels of P. Photograph courtesy of MW Shane and H Lambers. (Lower middle) Cross-sections of sun and shade leaves of Fagus crenata Blume. Sun leaves of F. crenata have two-cell-layered palisade tissue while shade leaves have one-cell-layered palisade tissue. The number of cell layers is determined when leaf primordia develop in winter buds. Photograph courtesy of I Terashima. (Bottom) A view of alpine vegetation from the summit of Mt Tallac, California, overlooking Desolation valley. The C4 grass Muhlenbergia richardsonis is present in the foreground as the darker-green tuft of grass between the rocks. The presence of C4 plants in the alpine zone demonstrates that C4 photosynthesis is not inherently unstable at low temperature. However, alpine C4 species are restricted to microsites that warm to above 25 °C during the day, indicating that C4 photosynthesis may have a reduced capacity to acclimate to cool conditions relative to C3 alpine species. Photograph courtesy of RF Sage.
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