ATYPICAL MAGNESIUM REQUIREMENTS IN A PHYLLITE POPULATION OF RARE PLANT SPECIES, PEDIOMELUM PIEDMONTATUM

Abstract

Pediomelum piedmontanum, Dixie Mt. Breadroot, is a rare legume species that was discovered in 2006. Currently, there are only three known populations, which are growing in either serpentine or phyllite soil. Both soil types contain extremely high concentrations of Mg as well as some other heavy metals. Previous experiments have revealed that propagation of P. piedmontanum is unsuccessful in potting soil, with high levels of mortality approximately two months after germination. Since Mg is unusually high in both soil types, it was hypothesized that survivability and growth of seedlings would be greater with Mg enriched soil than in potting soil. In order to test this hypothesis, seedlings from a phyllite population (7 plants/pot with 3 replicate pots/Mg group and 2 pots/control) were transplanted into one of the following potting soil enrichments: 50μM MgSO4, 100μM MgSO4 or controls with no Mg enrichment. During 12 weeks, seedlings in 100μM Mg displayed the greatest survivability and shoot growth, with the lowest survivability in control pots. Atypical Mg requirements have been noted in the literature for some plants adapted to serpentine soil, but this is a unique discovery for a population adapted to phyllite.