Contrasting Responses of Amur maackia and Black Locust to Culture in Hoagland Solution

Abstract

Hydroponic culture of tree seedlings is commonly used to study root biology; however, we have found that species differ in their responses to this practice. Responses of 2-week-old seedlings of Amur maackia (Maackia amurensis Rupr. & Maxim.) and black locust (Robinia pseudoacacia L.) to 1%, 5%, 10%, 25%, 50%, and 100% Hoagland solution #1 were determined over 5 weeks. Dry mass of black locust increased with increasing solution concentration up to 50%. For Amur maackia, dry mass was highest in 5% solution, and dry mass declined by ≈50% in 50% solution. Purpling, chlorosis, and necrosis occurred on leaves of Amur maackia in solutions ≥10%, and symptom severity increased with solution strength. Amur maackia leaf ion content increased dramatically with increasing solution strength; for instance, leaf P content increased 688% as solution strength increased from 5% to 50%. No symptoms occurred on Amur maackia grown in a soil-based medium and irrigated with 50% solution. These data indicate that black locust can be grown hydroponically using standard methods. However, growth of Amur maackia is inhibited at high solution concentrations, suggesting a sensitivity to the availability of ions, and perhaps an enhanced ability to sequester ions from its media.