Extraction methods for assessing the availability of cations for epiphytic lichens from bark

Concentrations of K, Ca, Mg, Fe, Mn, Zn, and Cu in water eluates as well as in SrCl2 and EDTA extracts of ground bark from Abies balsamea and Picea rubens were determined and related to total concentrations obtained from acid digests. SrCl2 was most effective at extracting K, Ca and Mg, whereas EDTA had a higher extraction efficacy for Fe, Mn. Zn. and Cu. Concentrations in the water eluates were generally lower. Mobility of the different metals in the bark was estimated as the percentage of the metal concentration recovered in the water eluates related to the total concentration; it decreased in the order K > Mg, Mn, Cu > Zn Ca, Fe. Concentrations of K, Mg, Mn, and Zn in the water eluates. the SrCl2 and EDTA extracts were correlated with total concentrations;, in these cases the choice of extraction method has little impact on the detection of correlations between element concentrations and epiphytic lichen abundance. For Ca, Fe and Cu little correlation occurred between concentrations in the extracts and total concentrations; here, possible relationships between epiphytic lichen abundance and element availability can easily be overlooked due to insufficient extraction methods. Cation availability depends on the phorophyte species and its vitality; thus, ion availability has to be determined seperately for each type of substrate. (C) 2002 Elsevier Science B.V. All rights reserved.