Plant survival on gypsum soils (>60% CaSO4 · 2H2O) has received relatively little scientific attention compared to saline, calcareous, or serpentine soils, despite the fact that gypsum is globally common in aridlands. Gypsum endemics exhibit three main patterns of edaphic adaptation. Old-lineage gypsophiles are widely distributed, found exclusively on gypsum soils, and accumulate high Ca and S concentrations in leaf tissues. Young-lineage gypsophiles and gypsovags exhibit more moderate Ca and S concentrations, with the former more narrowly distributed and the latter found on both gypsum and non-gypsum soils. Recent analyses of Brassicaceous old-lineage gypsophiles suggest that members of this family can accumulate high tissue S levels without forming the gypsum crystals observed in other old-lineage gypsophiles. Here, our objective was to test the hypothesis that gypsum endemic Brassicaceae have adapted to high-sulfate soils by using sulfur-rich defensive metabolites called glucosinolates as a metabolic S sink. We quantified total glucosinolates in vegetative tissues from gypsophile-gypsovag congener pairs of Nerisyrenia and Lepidium growing on and off gypsum. Nutrient analyses of vegetative tissues and associated soils allowed us to quantify the proportion of tissue S held as glucosinolates and evaluate the influence of local edaphic conditions on glucosinolate concentrations.
Results/Conclusions
Initial results indicate preliminary support for the idea that glucosinolates provide an adaptive advantage in colonizing gypsum soils. The gypsophile Nerisyrenia linearifolia exhibited higher glucosinolate concentrations than both its gypsovag congener Nerisyrenia camporum and the gypsovag Lepidium alyssoides. While the two Nerisyrenia congeners were found only at separate sites with distinct edaphic conditions in this study, N. linearifolia exhibited higher concentrations of glucosinolates than L. alyssoides located at the same site. Extensive research on glucosinolate metabolism in Brassicaceae of agricultural importance has previously demonstrated widespread phenotypic plasticity in response to soil S availability. Our results suggest that phenotypic plasticity may be less relevant than edaphic type in determining glucosinolate concentrations in vegetative tissues of gypsum endemic Brassicaceae.