Effects of Elevated C02 and Shade on Growth and Physiology in Five Northern Tree Species

Project Overview
Project Abstract: 
Our overall goal is to improve the understanding of forest ecosystem successional dynamics of differing shade-tolerant species under elevated CO2 conditions. We will compare four co-occurring deciduous angiosperm species (Acer saccharaum, Fagus grandifolia, Prunus serotina, Betula papyrifera) and one evergreen coniferous species having contrasting ranges of reported shade-tolerance. Two species of angiosperms will be shade tolerant, contrasted against two that are shade intolerant. Using open-topped chambers at the University of Michigan Biological Station in Northern Lower Michigan, one-year-old seedlings will be grown in a full factorial, randomized split-plot design that includes two partial pressures of CO2 (p[CO2]; ambient and elevated) (Mikan et al., 2000) and two levels of light, reflecting the average aspen forest understory and very low light micro-sites. Experiments will be conducted over two growing seasons (2001-2002) with possible continuation into 2003. We hypothesize that under elevated CO2 and deep shade conditions, late successional, shade tolerant species will have larger increases in relative growth rates and photosynthesis (especially in sunflecks) compared to the less shade tolerant, early successional species. Furthermore, we expect the shade tolerant species to exhibit decreased leaf dark respiration rates and leaf nitrogen content in deep shade compared to the intolerant species at both ambient and elevated CO2, which reduces C losses to the atmosphere and enhances seedling survival. Thirdly, we also hypothesize that at higher light levels, shade intolerant species will have larger increases in relative growth rates and photosynthesis than the tolerant ones in contrast to the first hypothesis. This research will help generate models to predict future changes in forest species composition based on plant physiological principles and ecological strategies. If there is a species shift toward one regenerative strategy due to increased atmospheric CO2, this could alter community composition and ecosystem function in a way that could affect the sustainability and management of forest systems in the future.
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