SENSITIVITY OF TREE SEEDLINGS TO ALUMINUM .1. HONEYLOCUST

Literature about the effects of Al on trees is reviewed in this article, emphasizing factors to consider when interpreting how seedling growth responds to Al. This article integrates two soil and two hydroponic studies that examine how honeylocust (Gleditsia tricanthos L.) seedlings respond to Al. The studies determined that honeylocust is the most Al-sensitive forest tree to have been studied in detail. Plant biomass and root number declined as Al in the soil or hydroponic solution increased. Growth was most consistently related to e({13+}) ({Al3+} is the Al3+ activity in the solution) or to the ratio of MAL/Ca (MAL is inorganic monomeric Al). In our study root number declined 50% between 0 and 0.05 mM MAL (0 to 0.012 mM {Al3+}). Root weight was also negatively related to root Al and positively related to root Ca. Levels of solution MAL/Ca and {Al3+} associated with more than 20% reductions in honeylocust growth were found in lysimeter solutions collected from a number of forested watersheds. However, such levels are probably not common in the natural edaphic range of honeylocust.