Do Armeria maritima (Mill.) Willd. ecotypes from metalliferous soils and non-metalliferous soils differ in growth response under Zn stress? A comparison by a new artificial soil method

Abstract

Morphological and biogeographical evidence suggests that the heavy-metal ecotype of Armeria maritima (Mill.) Willd. has evolved from a hybrid group between the subspecies maritima from salt marshes and the subspecies elongata from sandy soils. As part of a study on the ecotypic differentiation in A. maritima, Zn resistance was compared in populations from these three ecotypes. To study the long-term growth response to elevated Zn concentrations, an artificial soil was made from ion-exchange resin embedded in an inert sand matrix, in which metal ions were buffered by an ion-exchange system as in natural soils. In contrast to hydroponics, this artificial soil systems is suitable for long-term cultivation and it provides more reproducible growth conditions than a soil system. The long-term growth response in the artificial soil system was compared to the growth response to elevated Zn concentrations in a sand nutrient-solution system. In short-term tests, populations from non-metalliferous soils were more sensitive to Zn concentrations of 1.0 mmol l-1 than the heavy-metal populations. However, in long-term tests, the growth of adult plants from all populations was not inhibited by Zn concentrations up to 2.8 mmol kg-1 dry soil (equivalent 26% of cation-exchange capacity). The Zn resistance of all populations could therefore be sufficient for their survival on Zn mine soils. The discrepancy between longterm tests and short-term tests is discussed with respect to the hypothesis that 'sensitive' populations may differ from 'resistant' populations in the expression of Zn-resistance mechanisms.