William K. Smith

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Leaves of many evergreen angiosperm species turn red under high light during winter due to the production of anthocyanin pigments, while leaves of other species remain green. There is currently no explanation for why some evergreen species exhibit winter reddening while others do not. Conditions associated with low leaf water potentials (Psi) have been(More)
The influence of shoot structure on net photosynthesis was evaluated under field conditions for the central Rocky Mountain (United States) conifers Picea engelmannii (Parry ex Engelm.), Abies lasiocarpa ([Hook] Nutt.), and Pinus contorta (Engelm.). In all species, the greater number of needles per unit stem length on sun shoots correlated with a smaller(More)
Climate warming predicts changes to the frequency and height of cloud-immersion events in mountain communities. Threatened southern Appalachian spruce–fir forests have been suggested to persist because of frequent periods of cloud immersion. These relic forests exist on only seven mountaintop areas, grow only above ca. 1,500 m elevation (maximum 2,037 m),(More)
Cloud immersion can provide a potentially important moisture subsidy to plants in areas of frequent fog including the threatened spruce-fir communities of the southern Appalachian Mountains (USA). These mountaintop communities grow only above ~1,500 m elevation, harbor the endemic Abies fraseri, and have been proposed to exist because of frequent cloud(More)
Frequent cloud immersion events result in direct uptake of cloud water and improve plant water potentials during daylight hours in saplings of two dominant cloud forest species. In ecosystems with frequent cloud immersion, the influence on plant water balance can be important. While cloud immersion can reduce plant water loss via transpiration, recent(More)
A red/purple coloration of lower (abaxial) leaf surfaces is commonly observed in deeply-shaded understorey plants, especially in the tropics. However, the functional significance of red abaxial coloration, including its role in photosynthetic adaptation, remains unclear. The objective of this study was to test the back-scatter hypothesis for abaxial leaf(More)
Anthocyanins in upper (adaxial) leaf tissues provide greater photoprotection than in lower (abaxial) tissues, but also predispose tissues to increased shade acclimation and, consequently, reduced photosynthetic capacity. Abaxial anthocyanins may be a compromise between these costs/benefits. Plants adapted to shaded understory environments often exhibit(More)
Wetlands represent the largest natural source of methane flux to the atmosphere, which can occur across the sediment/water/plant-atmosphere interface. Of these three potential methane sources, the role of vegetation in this flux is the least well understood. Both living and dead herbaceous vegetation have been demonstrated to act as methane sources, while(More)
Recent studies have shown that photosynthesis may increase under diffuse light regimes (e.g., cloud-generated) compared to direct (collimated) irradiance at the canopy and ecosystem levels. Yet, there are few comparative studies for individual species at the branch or leaf level. One of the strongest contrasts in the plant kingdom is the architectural(More)
Alpine plants experience high levels of insolation, as well as cold nighttime temperatures throughout the summer growth period. These two stress factors in combination are now recognized as potentially important limitations to photosynthetic carbon gain. Although likely candidates, the possible occurrence of photoinhibition in alpine plants has been(More)