Carolyn J. McQuattie

Effect of water stress on aluminum toxicity in pitch pine seedlings

Abstract A decrease in soil water content during droughts may increase aluminum (Al) to concentrations that are toxic to the growth of trees. The effects of water stress (WS) on the response of ectomycorrhizal pitch pine (Pinus rigida Mill.) seedlings to aluminum was determined by growing seedlings in sand irrigated with nutrient solution (pH 3.8) containing 0, 5, or 10 mg L‐1 Al. Water stress was imposed for 41 days by withholding nutrient solution for five consecutive days each week. At harvest time, seedlings at high WS had 72% of mean gravimetric water contents of seedlings at low WS. Aluminum decreased growth of seedlings at high WS, but had no effect on growth of seedlings at low WS. Aluminum toxicity symptoms in roots (e.g., dark thickened tips) were observed at lower Al levels at high WS than at low WS. Stem dry weight was the only plant part decreased by water stress alone. Across Al levels, Al concentration in roots was higher at low WS than at high WS. Water stress alone reduced root [phosphorus (P), potassium (K), and calcium (Ca)] and foliar [P, K, and magnesium (Mg)] concentrations of mineral nutrients. Decreases of nutrients in roots with increasing Al was greater at low than at high WS. Calcium was the only foliar nutrient decreased by Al treatment.

Effect of nitrogen source on aluminum toxicity in nonmycorrhizal and ectomycorrhizal pitch pine seedling

Abstract The effect of elevated nitrate [(NO3‐nitrogen (N)] or ammonium (NH4)‐N on the response of nonmycorrhizal (NM) and ectomycorrhizal (ECM) pitch pine (Pintis rigida Mill.) seedlings to aluminum (Al) was determined in experiments in which N was increased three times above ambient levels. Seedlings with and without the mycorrhizal fungus Pisolithus tinctorius (Pers.) Coker & Couch were grown in sand irrigated with nutrient solution (pH 3.8) containing 0, 10, or 20 mg Al L‐1 (0, 370, or 740 μM Al). The nutrient solution simulated that for the sandy, nutrient‐poor soil of the New Jersey Pine Barrens. Elevated NO3‐N had no significant effect on Al toxicity in NM seedlings, but Al toxicity at ambient NH4‐N was ameliorated by elevated NH4‐N. Symptoms of Al toxicity in roots (thick and stunted) of ECM seedlings at ambient N levels were reduced by elevated NH4‐N and absent at elevated NO3‐N. When N was elevated by an increase in NO3‐N or NH4‐N, uptake of N and relative increases in total biomass were greater...

Stimulatory effects of aluminum on growth of sugar maple seedlings

ABSTRACT To determine the effect of aluminum (Al) on sugar maple (Acer saccharum Marsh.), seedlings were grown in sand irrigated with nutrient solution (pH 3.8) containing 0, 2.5, 5, 10, 20, or 40 mg L−1Al. Seedling growth was enhanced at 2.5 and 5 mg L−1Al. Although higher levels of Al reduced calcium (Ca) and magnesium (Mg) concentrations in leaves and caused root and foliar injury, no negative effects of Al on growth were observed.

Effect of manganese on endomycorrhizal sugar maple seedlings

Abstract Manganese (Mn) toxicity may play an important role in the poor survival of seedlings in declining sugar maple (Acer saccharum Marsh.) stands in northern Pennsylvania. To determine the effect of Mn on the growth of sugar maple seedlings, 1‐year‐old seedlings inoculated with vesicular‐arbuscular mycorrhizal (VAM) fungi and growing in sand‐vermiculite‐peat moss medium were irrigated for 7 weeks with nutrient solution (pH 5) containing 0.1 (control), 1, 2, 4, 8, or 16 mg L−1 Mn. Total seedling dry weight was negatively correlated with Mn, becoming significantly different than the control at 2 mg L−1 Mn. Stem and root dry weight were reduced by lower Mn levels than leaf dry weight. Manganese had no effect on the root/shoot ratio. The concentration of Mn in roots and leaves increased as the level of Mn in the nutrient solution increased, with the concentration in the leaves 2.2‐ to 3.7‐fold greater than the concentration in the roots. Except for a reduction of P in the roots, Mn had little effect on the concentration of nutrient elements in the roots or leaves. Colonization of the roots by VAM fungi was increased by Mn, with a maximum percentage at 4 mg L−1 Mn. Manganese toxicity symptoms in the leaves, small discrete chlorotic spots, began to appear at 1 mg L−1 Mn. The sensitivity of sugar maple seedlings to Mn found in this study supports the hypothesis that Mn may affect regeneration in declining sugar maple stands. However, evaluation of the effects of Mn on seedlings in native soils under field conditions will be necessary before the role of Mn in sugar maple regeneration can be understood.