Growth, biomass distribution and CO2 exchange of northern hardwood seedlings in high and low light: relationships with successional status and shade tolerance.

The physiology, morphology and growth of first-year Betula papyrifera Marsh., Betula alleghaniensis Britton, Ostrya virginiana (Mill.) K. Koch, Acer saccharum Marsh., and Quercus rubra L. seedlings, which differ widely in reported successional affinity and shade tolerance, were compared in a controlled high-resource environment. Relative to late-successional, shade-tolerant Acer and Ostrya species, early-successional, shade-intolerant Betula species had high relative growth rates (RGR) and high rates of photosynthesis, nitrogen uptake and respiration when grown in high light. Fire-adapted Quercus rubra had intermediate photosynthetic rates, but had the lowest RGR and leaf area ratio and the highest root weight ratio of any species. Interspecific variation in RGR in high light was positively correlated with allocation to leaves and rates of photosynthesis and respiration, and negatively related to seed mass and leaf mass per unit area. Despite higher respiration rates, early-successional Betula papyrifera lost a lower percentage of daily photosynthetic CO2 gain to respiration than other species in high light. A subset comprised of the three Betulaceae family members was also grown in low light. As in high light, low-light grown Betula species had higher growth rates than tolerant Ostrya virainiana. The rapid growth habit of sarly-successional species in low light was associated with a higher proportion of biomass distributed to leaves, lower leaf mass per unit area, a lower proportion of biomass in roots, and a greater height per unit stem mass. Variation in these traits is discussed in terms of reported species ecologies in a resource availability context.