Predicting Phenotypic and Genotypic Response of the Dominant Prairie Grass Andropogon gerardii to Climate Change in the US Central Grasslands

Andropogon gerardii is an ecologically dominant grass in the Midwest. With its wide distribution across climate gradients, it becomes urgent to understand phenotypic and genetic variation to predict response to current and future climates. We characterized phenotypes and genotypes of 30 populations across precipitation (40-119cm/yr) and temperature gradients (5-15^oC) and incorporated intraspecific variation into species distribution models of current and predicted response under climate change. We grew plants from seed in the greenhouse and measured blade width, height, biomass, and chlorophyll absorbance, and genotyped to assess genetic diversity and divergence. We used phenotypes as input into SDMs to predict current and future phenotypes under climate change and investigated genetic divergence and outlier SNPs. Analysis shows a main effect among population phenotypes (height, width, biomass, and chlorophyll absorbance P<0.001). PCA show a phenotypic cline across populations that is mainly explained by rainfall. The distribution model for 2070 predicts that short-statured, dwarfed phenotypes found in the present-day dry shortgrass prairies of the west will become favored ~800 km eastward while robust, tallgrass phenotypes of current core will become favored ~700 km northeastward of their current location. We identified 7,318 SNPs and evidence of four genetic groups (Western Plains, Ohio Valley, Upper Midwest, Northern Plains). The greatest genetic diversity currently occurs in the Central Great Plains where genetic groups converge, but is likely to be diminished under future climates. Outlier analysis identified 197 SNPs under divergent selection and were associated with various aspects of precipitation. These results portend large future shifts in genotypes and phenotypes. Sourcing plant material for grassland and rangeland restoration should anticipate changes favored under future climates.