Ecological Genomics in the Johnson Lab focuses on the genetic, molecular and ecological mechanisms involved in adapatation of the prairie grass big bluestem Andropogon gerardii to diverse and changing climates of the Great Plains. This warm season C4 grass has a widespread distribution, extending from the east coast of North America to the Great Plains where it covers vast areas of the prairie landscape and represents as much as 80% of the plant biomass, until petering out at the limit of its distribution in western KS and eastern Colorado. Big bluestem is a long-lived perennial that is widely used in prairie restorations. In 2007 alone, over 800,000 acres just in Kansas were restored to tall grass species with big bluestem one of the most abundant. Among natural populations, big bluestem shows a striking cline in morphology and physiology in drought adaptation over the 3-fold difference in annual precipitation across the Great Plains (1200 mm/yr in Illinois to 400 mm/yr in Western Kansas). The overall objective of the Johnson Lab is to uncover the genetic and molecular basis for the sharp ecotypic variation across the Great Plains. Our lab uses approaches such as gene expression analysis using RNA-seq and Genotype by sequencing to identify candidate genes that may be important to drought response or other environmental changes. We complement the genetic work with experimental manipulations and reciprocal garden studies in the field and use the full suite of phenotypic characterizations i.e., physiological measures such as chlorophyll florescence, water use efficiency, photosynthetic rates, and morphological parameters such as specific leaf area, leaf thickness, relatively growth rates, leaf area and biomass, and root:shoot. We also use a comparative approach by investigating big bluestem's drought adapted sister species sand bluestem A. halli. Our ultimate goal is to discover how the ecologically dominant big bluestem tall grass can adjust to current sharp precipitation gradients and make predictions about its ability to respond to future and increasingly novel climates using MAXENT modeling. This work also has conservation implications as it will help to inform land managers about the importance of using local ecotypes in prairie restorations and the response of those ecotypes to predicted climate change.
Andropogon virginicus- Rapid Evolution in an Anthropogenically Altered Environment A new area of ecological genomics research in the Johnson Lab is focused on adaptive response to anthropogenic change in the perennial old-field grass Andropogon virginicus. This species is native to the eastern United States and central Great Plains where it often grows in degraded landscapes and in nutrient poor soil. A. virginicus is known to develop distinct ecotypes in response to extreme environments such as granite outcroppings and coal mine tailings. Our research focuses on populations of A. virgnicius growing in the Tar Creek Superfund Site, an abandoned Lead and Zinc mine spanning southeastern Kansas, northeastern Oklahoma, and southwestern Missouri. We are able to take advantage of a variety of interdisciplinary approaches to compare A. virginicus populations in the mine sites and those in nearby uncontaminated sites in order to investigate mechanisms of heavy metal tolerance and evidence of local adaptation. Through analysis of phenotypic, genotypic, and gene expression data, we aim to tease apart the roles of DNA sequence evolution and phenotypic plasticity that enable mine site populations to persist in a highly altered and contaminated environment. This work has the potential to help guide seed sourcing decisions during the continued restoration of the Tar Creek Superfund Site, especially if locally adapted A. virginicus ecotypes are identified.