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 dynamics of aluminium in the rhizosphere. The aim of this paper is to present a suitable method for studying rhizosphere Al dynamics. It is based on the use of agarose as a substrate for plant growth. Agar and agarose gels are often used in rhizosphere studies, but most are poorly characterized and occasionally give rise to experimental artefacts, especially with low mobility elements like Al. The results reported here show that agarose is a relatively pure substrate, nearly devoid of phosphorus and other Al-complexing substances. Aqueous extracts of agarose also exhibit Al phytotoxicity equivalent to that of a nutrient solution. Since this substrate has the properties of a variable charge exchange complex, it can be considered as a physico-chemical model for organic matter. Finally, its Al adsorption capacity is high enough for the 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 rhizophere.