Ayres Abstracts
| Canny, D.S., Ayres, M.P., and J.J. Ruel. Stategies of carbon acquisition in Viburnum alnifolium (Caprifoliaceae). Submitted to Canadian Journal of Forest Research. Full text in pdf. |
| Viburnum alnifolium (Caprifoliaceae) is a common understory shrub in northeastern North America. Its leaves expand earlier in the spring than canopy trees, which allows access to high irradiance but also exposes them to freezing temperatures. V. alnifolium leaves tolerated temperatures to -5° C, which is lower than that tolerated by other woody plants in the community. This permits early leaf-out with minimal risk of freezing damage. Measurements of photosynthetic light responses and understory irradiance indicated that the net annual photosynthesis of V. alnifolium leaves are increased by 40% as a result of spring carbon assimilation before canopy closure. Maximum assimilation rates (Amax) were highest in early summer (5.5 vs. 3.2 µmoles C m-2 s-1 in early summer vs. midsummer), which allowed V. alnifolium to better exploit the high irradiance that it encounters before canopy closure. High Amax in spring was associated with high concentrations of leaf nitrogen. Throughout the season, V. alnifolium leaves had very low light compensation points (7 ± 2 µmoles m-2 s-1) and dark respiration rates (0.34 ± 0.10 µmoles C m-2 s-1), which allowed the plant to maintain a positive carbon budget on most days even after canopy closure. V. alnifolium possesses an unusual carbon acquisition strategy that affords it access to significantly increased irradiance early in the season with minimal freeze risk and permits a positive carbon balance throughout the remainder of the growing season. |
| Photosynthesis, light response, acclimatization, super cooling point, cold tolerance, carbon budget, understory, Viburnum alnifolium |