Responses of Quaking Aspen Seedlings to Solution Calcium and Aluminum

Abstract

Quaking aspen (Populus tremuloides Michx.) seedlings were grown in nutrient solutions to study their responses to various levels of calcium (Ca) and aluminum (Al) in four experiments. In solutions with 100 to 2500 µM Al, seedlings had visible symptoms of Al toxicity and/or Al‐induced deficiencies of Ca or phosphorus (P). The symptoms became more prominent with increasing solution Al, and less prominent with increasing solution Ca. Elongation of shoots and roots declined significantly with increasing solution Al, and usually increased with increasing solution Ca. Therefore, elongation of shoots and roots was closely related to ratio of solution Ca/Al. The molar ratio of solution Ca/Al associated with 90% of maximum elongation was 0.23 for shoots and 1.86 for roots. The levels of solution magnesium (Mg) and NH₄ did not significantly affect the response of aspen to solution Ca/Al ratio. Concentrations of leaf Ca, nitrogen (N), and Mg as well as root Ca, potassium (K) and Mg decreased as solution Al increased, whereas leaf Ca, N, and P and root Ca and K usually increased with increasing solution Ca. Adding Al into solutions increased leaf and root Al. Shoot elongation was positively and closely related to the root Ca/Al ratio, while root elongation was positively and closely related to root Ca. In addition, aspen growth was significantly related to tissue N and K. These relationships indicate that Ca deficiency was a primary, but probably not the sole cause of growth reduction in solutions with high Al.

Keywords:

• Calcium
• Calcium aluminum ratio
• Populus tremuloides

Acknowledgments

This research was supported by the Minnesota Agricultural Experiment Station and by the Minnesota Legislative Commission on Natural Resources. We appreciate the valuable advice from Dr. Paul Bloom, Dr. David Grigal, and Dr. Mark Tjoelker. We are thankful for the technical assistance provided by Cindy Buschena.