AGAROSE AS A SUITABLE SUBSTRATE FOR USE IN THE STUDY OF AL DYNAMICS IN THE RHIZOSPHERE

Because of experimental difficulties, few authors have studied the dyn amics of aluminium in the rhizosphere. The aim of this paper is to pre sent a suitable method for studying rhizosphere Al dynamics. It is bas ed on the use of agarose as a substrate for plant growth. Agar and aga rose gels are often used in rhizosphere studies, but most are poorly c haracterized and occasionally give rise to experimental artefacts, esp ecially with low mobility elements like Al. The results reported here show that agarose is a relatively pure substrate, nearly devoid of pho sphorus and other Al-complexing substances. Aqueous extracts of agaros e also exhibit Al phytotoxicity equivalent to that of a nutrient solut ion. Since this substrate has the properties of a variable charge exch ange complex, it can be considered as a physico-chemical model for org anic matter. Finally, its Al adsorption capacity is high enough for th e Al reserve in the substrate not to exert a limiting effect on plants and low enough to allow accurate measurement of Al depletion in the r hizophere.