Leaf sodium, potassium and electrolyte accumulation capacity of plant species from salt-affected coastal habitats of the Baltic Sea: Towards a definition of Na hyperaccumulation

Abstract

The aim of the present study was to compare a relatively large number of native plant species from salt-affected coastal habitats with respect to their Na+ and K+ accumulation capacity and electrolyte level in leaves. Sampling sites (77 in total) were chosen during field survey in coastal habitats located at geographically distant places along the Baltic Sea in the territory of Latvia, Estonia, Denmark and Sweden. The main criterion for selection of sampling sites was minimum average soil electrical conductivity (EC) above 200 mS m–1. Leaf samples of 102 taxa (species) from 34 families were collected, with a total number of samples reaching 502, and their water content, Na+ and K+ concentration, and electrical conductivity in water extracts were analyzed. High intraspecies and interspecies variability in analyzed parameters was found. Frequency distribution of Na+ concentration showed highly significant positive asymmetry and deviation from normality. Data on K+ concentration and tissue EC level had asymmetric distribution and deviation from normality but to a lesser extent than that for Na+. Correlation between tissue Na+ concentration and substrate EC at sampling sites was low on individual sample basis but increased to moderate level when mean values of species were analyzed. According to accumulation characteristics of Na+ and K+ in leaves, all species corresponded to one of three general groups: Na+ excluders, regulating EC by changes in K+ concentration; K+ excluders, regulating EC by changes in Na+ concentration; and tight EC regulators; but these features were evident only when intraspecies variability was considered. Na+ concentrations in a range 18 to 30 g kg–1 (on dry biomass basis) and 0.24 to 0.30 mol L–1 (on tissue water basis) can be used as approximate values of a "normal" vs "hyperaccumulation" Na+ range in leaves of coastal plant species of the Baltic Sea.