RESPONSES OF 3 DECIDUOUS TREE SPECIES TO ATMOSPHERIC CO2 AND SOIL NO3- AVAILABILITY

This research evaluated the direct and interactive effects of atmosphe ric CO2 and soil NO3- availability on growth and biomass partitioning of quaking aspen (Populus tremuloides Michx.), red oak (Quercus rubra L.), and sugar maple (Acer saccharum Marsh.). In the split split plot experimental design, NO3- availability (low and high) and tree species were nested in two levels of atmospheric CO2 (ambient, 355 mu L/L; el evated, 650 mu L/L). Seedlings were grown for 57 days in environmental control rooms. Increased CO2 and NO3- availability positively and (mo stly) independently influenced total growth and relative growth rates. Moderate to weak interactions between CO2 and NO3- for several growth parameters (e.g., leaf production, shoot length, root collar diameter ) in some species indicated an enhanced response to CO2 enrichment und er conditions of high NO3- availability. Interactive effects were most pronounced in aspen. Seedling growth and allocation responses to CO2 and NO3- were frequently species specific and associated with successi onal status. For example, proportional increases in growth in response to elevated CO2 were greatest for sugar maple and least for quaking a spen, whereas the converse was hue with respect to response to high NO 3- availability. This research indicates that the impact of enriched C O2 atmospheres on forest communities will be influenced by both nutrie nt availability and unique species characteristics.