Taxonomy & Evolution

Impacts of land use on the stress responses of an invasive grass

Can ecotypic origin (i.e. agricultural vs. non-agricultural) and environmental selection pressures predict biomass accumulation in Johnsongrass?

Johnsongrass, a perennial invader on six continents, is established in both agricultural and non-agricultural habitats across the United States. Native to the Middle East, Johnsongrass was first introduced to the US in the 1820s as a forage crop though it quickly became weedy and invasive.

Across its vast introduced range, Johnsongrass exhibits dramatic genetic and phenotypic variation. While some of its success may be explained by phenotypic plasticity, there is reason to believe that different selection pressures among habitats have also occurred over time as ecotypic differentiation, for example agricultural populations may differ from non-agricultural populations.

 A dense Johnsongrass stand, displaying panicles in late anthesis to early seed formation, as well as characteristically prominent leaf midrib. Image credit: V. Lakoba.

In their recent publication in AoBP, Lakoba & Barney tested adaptation to water and nutrient stresses in five non-agricultural and five agricultural populations of the Johnsongrass (Sorghum halepense) sampled across a broad range of climates in the USA. They found that precipitation and soil fertility from the site of population origin mediated drought adaptation, while the latter also impacted the contrasting chlorophyll content of agricultural and non-agricultural ecotypes.

These findings suggest simultaneous rapid adaptation to climate, soil fertility, and land use occurred in the establishment of this invasive species. Notably, the non-agricultural ecotype, which emerged after intensive management in cropland, showed greater adaptation to nutrient-poor soils. Unfortunately, this suggests that invasive plants are poised to take on novel habitats within their introduced ranges in the future, leading to complications in the prevention and management of their spread.

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