Response of ectomycorrhizal and nonmycorrhizal pitch pine (Pinusrigida) seedlings to nutrient supply and aluminum: growth and mineral nutrition
Mycorrhizal colonization and nutrient supply may have important effects on aluminum toxicity in trees grown on acidic, nutrient-poor soils. The interacting effects of mycorrhizal inoculation, nutrient level, and Al treatment on growth and mineral nutrition of pitch pine (Pinusrigida Mill.) seedlings grown with and without the ectomycorrhizal fungus Pisolithustinctorius (Pers.) Coker & Couch were determined. The seedlings were grown for 66 days in sand irrigated with 0.1- or 0.2-strength nutrient solution (pH 3.8) containing 0, 10, or 20 mg/L Al (0, 0.37, or 0.74 mM). Across nutrient and Al levels total dry weight of ectomycorrhizal (ECM) seedlings was 75% greater than that of nonmycorrhizal (NM) seedlings. Doubling the nutrient level increased the dry weight of NM seedlings by 120%, versus 60% for ECM seedlings. Aluminum reduced root and shoot growth in NM seedlings, but had no effect on shoot growth and only a marginally significant effect on root growth of ECM seedlings. Shoot growth of NM seedlings was more sensitive to Al than root growth. Increased growth of NM seedlings by doubling the nutrient level was least at the highest Al level. Symptoms of Al toxicity in roots (dark, stunted tips) occurred at a lower Al level in NM than ECM seedlings. A strong relationship was not found between Al toxicity and concentrations of Mg and Ca in roots and needles. Enhancement of growth resulting from increased uptake of nutrients due to mycorrhizal inoculation (and) or an increased level of nutrients was the overriding factor affecting the response of pitch pine seedlings to Al.