INTERACTIVE ROLE OF ELEVATED CO2, NUTRIENT LIMITATIONS, AND WATER-STRESS IN THE GROWTH-RESPONSES OF RED SPRUCE SEEDLINGS

Red spruce (Picea rubens Sarg.) seedlings were grown from seed for 5 m o in ambient (362 ppm) or elevated (711 ppm) CO2 to determine the pote ntial effect of an increase in global CO2 concentration on seedling gr owth and establishment. CO2 exposure treatments were crossed with two levels of soil fertility and water stress treatments to determine if s eedling dry weight, size, and fixed growth responses to elevated CO2 d epended on nutrient and water supply. Seedling dry weight and size res ponses to elevated CO2 at 5 mo did not depend on nutrient and water su pply. Seedlings grown in both soil fertility treatments and water stre ss treatments responded similarly to CO2 treatment. Water stress and C O2 treatments did have an interactive influence on the fixed growth po tential of the terminal leader. Leaf weight, leaf area, and height of the terminal leader of water-stressed seedlings were greater in seedli ngs exposed to elevated CO2 during budset than seedlings exposed to am bient CO2. Total new fixed growth (lateral plus terminal) and total te rminal fixed growth (leaf plus stem) were greater in seedlings that fo rmed shoot primordia in elevated CO2 than in ambient CO2. Red spruce s eedlings grown in elevated CO2 for 5 mo had greater stem diameter, hei ght, branching density, leaf weight, root weight, stem weight, total w eight, and mean relative growth rate (RGR) from 3 to 5 mo than seedlin gs grown in ambient CO2. Red spruce seedling responses to elevated CO2 suggest that seedling establishment in natural environments may be en hanced when ambient CO2 concentrations rise even if water and nutrient availabilities are limited.