Phylogenetic patterns of foliar mineral nutrient accumulation among gypsophiles and their relatives in the Chihuahuan Desert.

Abstract

Gypsum endemism in plants (gypsophily) is common on gypsum outcrops worldwide, but little is known about the functional ecology of Chihuahuan Desert gypsophiles. We investigated whether leaf chemistry of gypsophile lineages from the northern Chihuahuan Desert are similar to leaves of related nonendemic (gypsovag) species relative to their soil chemistry. We expected widely distributed gypsophiles (hypothesized to be older lineages on gypsum) would have distinct leaf chemistry from narrowly distributed, relatively younger lineages endemic to gypsum and gypsovags, reflecting adaptation to gypsum. We collected leaves from 23 gypsophiles and related nonendemic taxa growing on nongypsum soils. Soils and leaves were analyzed for Ca, S, Mg, K, N, and P. Leaf gypsum was assessed using Fourier transform infrared spectroscopy. Most widespread gypsophile lineages that are hypothesized to be relatively old accumulate foliar S, Ca, and gypsum, but younger gypsophile lineages and closely related gypsovags do not. Young, narrowly distributed gypsophile lineages have leaf chemical signatures similar to nonendemic congeners and confamilials. Our data suggest multiple adaptive mechanisms support life on gypsum in Chihuahuan Desert gypsophiles. Most widespread gypsophiles are specialized for life on gypsum, likely due to shared abilities to accumulate and assimilate S and Ca in leaves. In contrast, narrowly distributed gypsophiles may have mechanisms to exclude excess S and Ca from their leaves, preventing toxicity. Future work will investigate the nutrient accumulation and exclusion patterns of other plant organs to determine at what level excess S and Ca uptake is restricted for young-lineage gypsophiles and gypsovags.