Differences in iron acquisition strategies of calcicole plant species from xerothermic grasslands

Little is known about iron (Fe) acquisition of calcicole species from xerothermic grasslands and their resistance to Fe-dependent chlorosis. In this study an experiment was designed to investigate effects of opposing soil types (acidic Podzol vs slightly alkaline Rendzina) and addition of HBED-chelated Fe (five doses of 5 and 25 μmol kg−1 soil every two weeks). Selected calcicole plant species occurring on xerothermic grasslands, Aster amellus L. (Aa), Betonica officinalis L. (Bo), Prunella grandiflora (L.) Scholler (Pg), Salvia verticillata L. (Sv) and Veronica teucrium L. (Vt), were tested in a pot experiment under field conditions. Responses of plants were described using measurements of chlorosis, growth, chlorophyll content and fluorescence, activity of antioxidant enzymes and content of elements, including Ca, Mg, Fe, Mn, Zn and Cu. Some Podzol-grown plants showed arrested growth (up to 80% significant reduction of root and shoot fresh weight (FW) compared to Rendzina-grown plant, depending on species) but no signs of Fe-dependent chlorosis, whereas the same species grown on Rendzina performed very differentially. Lime chlorosis on Rendzina was induced in Aa, Bo and Pg (c.a. 30–40% significant reduction of chlorophyll content compared to Fe-supplied plants) but not in Sv and Vt. Fe-HBED treatment totally diminished chlorosis in species-dependent dose (5 μmol kg−1 soil for Aa and Pg and 25 μmol kg−1 soil for Bo) but significantly slowed growth (up to 50% significant reduction of root FW and 65% reduction of shoot FW compared to non-Fe-treated Rendzina-grown plant, depending on species). Chlorosis negatively affected functioning of photosynthetic apparatus alternating quantum yield of primary PSII photochemistry (FV/FM), light energy dissipation (DI0/RC) and performance index (PIABS) and Fe-HBED significantly alleviated these perturbations. Activity of antioxidant enzymes suggested Fe-HBED-caused alleviation of oxidative stress. Reduction of chlorosis did not rely on improved Fe accumulation, nor on altered partitioning on root-shoot axis, but a relation between chlorosis and manganese (Mn) in roots was observed. The results seem to indicate more complex interaction between Fe and Mn in induction of soil-dependent chlorosis than one might expect. Availability of Fe on the slightly alkaline soil limited functioning of the studied calcicole species in specific manner and probably created micro habitats. Ultimately, it can be clearly seen that xerothermic grasslands are composed of chlorosis-resistant and chlorosis-susceptible species.