A balanced polymorphism in biomass resource allocation controlled by phosphate in grasses screened through arsenate tolerance

• This paper reports a detailed examination of how a polymorphism in arsenate tolerance in grasses from non-arsenic contaminated environments is maintained due to phosphate fertilization.
• This polymorphism will be of wide interest as it relates to phenotypic responses to phosphate, a fertiliser that is fast running out in a global context as it is a limited natural resource.
• The report details that the polymorphism is present in many more grasses, suggesting that the phenomenon studied widely occurs in the plant kingdom.

The response of arsenate and non-tolerant Holcus lanatus L. phenotypes, where tolerance is achieved through suppression of high affinity phosphate/arsenate root uptake, was investigated under different growth regimes to investigate why there is a polymorphism in tolerance found in populations growing on uncontaminated soil. Tolerant plants screened from an arsenic uncontaminated population differed, when grown on the soil from the populations origin, from non-tolerants, in their biomass allocation under phosphate fertilization: non-tolerants put more resources into tiller production and down regulated investment in root production under phosphate fertilization while tolerants tillered less effectively and did not alter resource allocation to shoot biomass under phosphate fertilization. The two phenotypes also differed in their shoot mineral status having higher concentrations of copper, cadmium, lead and manganese, but phosphorus status differed little, suggesting tight homeostasis. The polymorphism was also widely present (40%) in other wild grass species suggesting an important ecological role for this gene that can be screened through plant root response to arsenate.