THE EFFECTS OF ALUMINUM ON PICEA-RUBENS - FACTORIAL-EXPERIMENTS USINGSAND CULTURE

We used sand culture to examine the effects of aluminum (Al3+) on gas exchange and growth in 1+0 Picea rubens Sarg. seedlings. Growth soluti ons were prepared to match the elemental concentrations of the soil so lutions in a declining Abies balsamea (L.) Mill. - P. rubens stand. In our first experiment, we used a four-way factorial design to examine the interactions between Al, pH, nutrients, and CO2. All plants were n itrogen deficient. Photosynthetic rate and instantaneous water-use eff iciency both declined at 250 mu mol . L(-1) Al, as did the root/shoot ratio of the seedlings. Plant weight, however, was not significantly a ffected by the 10-fold increase in Al solution concentration. These re sults were robust across a range of experimental conditions, suggestin g that other aspects of soil acidification, such as NO3 fertilization in N deficient soils, could counteract the toxic effects of Al. In a s econd experiment, we examined the effects of subtoxic concentrations o f Al at two levels of nutrient cation availability. Unlike in a previo us study, cation fertilization affected neither gas exchange nor growt h. While the decreases in root/shoot ratio and growth were expected at 250 mu mol . L(-1) Al, the peak in growth rates for intermediate conc entrations of Al (25-100 mu mol . L(-1)) was not. The latter result wa s interpreted in light of the positive effects that low concentrations of Al are known to have on other species.