“Specialization to extremely low-nutrient soils limits the nutritional adaptability of plant lineages”

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G. Anthony Verboom, William D. Stock, and Michael D. Cramer

Foliar stoichiometry indicates that specialization to extremely poor soils limits the nutritional adaptability of plants

The evolutionary consequences of nutritional specialization in plants

A patch of mountain fynbos vegetation in the vicinity of Landdroskop in the Cape Floristic Region of South Africa. The image captures Erica fastigiata L. (Ericaceae) growing in a matrix of Restionaceae. The underlying soils are sandy and infertile, being derived from ancient Table Mountain Group quartzites.
(Credit: G. Anthony Verboom)

Specialization offers clear benefits in a competitive world but it also has its downsides, especially a loss of versatility. This is as true evolutionarily as it is in the professional world. In a paper appearing in The American Naturalist, Verboom et al. use data for a range of plants sampled from the Cape flora of South Africa to show that the leaf concentrations of physiologically important nutrients such as phosphorus and potassium have a strong genetic basis and are highly regulated, with variation between plant lineages reflecting adaptation to the environments in which they occur. They also show that the rate at which leaf nutrient concentrations evolve differs between lineages, these attributes being least “flexible” in lineages (e.g. Ericaceae, Proteaceae, Restionaceae) which associate almost exclusively with the highly infertile fynbos heathlands of the Cape region. Conservatism in the nutritional attributes of low-nutrient, fynbos-specialist lineages probably explains why the fynbos flora is so different taxonomically from that of the surrounding vegetation, which for the most part associates with more fertile soils. It also suggests that fynbos-specialist lineages should be less predisposed to speciation via adaptation to soils of contrasting fertility than are non-specialist lineages. This is important for our understanding of why the Cape flora is so rich, particularly given the considerable importance accorded to geological and soil heterogeneity as a driver of plant speciation in the Cape. Read the Article