Poor competitors find refuge amongst specialists

Until recently I knew gypsum, CaSO₄·2H₂O, mainly as a component of some paints and as an insulating material in the building industry. It certainly does not appear to be a very promising substrate for plant growth. Thus, Palacio et al. (Xaragoza and Móstoles, Spain and St Paul, MN, USA, pp. 333–343) state that gypsum soils often form a hard surface crust that makes germination difficult; they tend to be mechanically unstable with unpredictable water relations, while their basic chemistry includes not only excesses of Ca and S, but also of Mg. Although these features may compromise plant survival, there are plants that grow and even thrive on gypsum soils. The authors suggest that these fall into two categories: gypsovags, gypsum-tolerant plants that find refuge in this stressful environment as a strategy for avoiding competition; and true gypsum specialists or gypsophiles that are more or less confined to gypsum soils. Based on their work in

Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk