Genotypes of a tallgrass prairie species respond differently to drought, despite high plasticity within populations
Natural and anthropogenic effects are expected to make future global climate change more unpredictable and extreme. While some species may succumb to these extremes, such as heat waves and drought, other species may have the capacity to cope with a changing environment, either through increased genetic diversity, increased plasticity, or both. In dominant species, high genetic diversity and intraspecific variation may allow genotypes to fluctuate in abundance in response to stress while maintaining ecosystem function, allowing within-population adaptation and evolution. The common C4 tallgrass species Andropogon gerardii has high genetic diversity and appears to be plastic in response to changing water availability. In this study, we ask the question, do common genotypes of A. gerardii differ in their response to a gradient of water stress? From a single population, we selected three A. gerardii genotypes (G2, G5, and G11) that previously responded differently to drought conditions in the field. We subjected individual plants to a gradient of moisture conditions (non-limiting to typical drought) over ten weeks and examined instantaneous physiological (photosynthesis, stomatal conductance, leaf water potential) and cumulative phenotypic (growth, root and shoot biomass allocation) responses to the different water treatments. Recovery and flowering following the drought were also examined.
A. gerardii genotypes exhibited high plasticity in their physiological responses and biomass allocation patterns. As expected, genotypes were most stressed (lowest growth, photosynthesis, conductance, leaf water potential) under the most limiting water treatment, but recovered physiological processes during recovery. This indicates similar coping strategies (rapid plastic response) among genotypes under drought. However, genotypes responded differently to the treatments in terms of growth allocation and flowering. G5 was tallest, fastest growing, and had highest leaf area under more wet conditions. In contrast, G11 grew more slowly, allocated more biomass belowground, and had more numerous small, rolled leaves, suggesting that this genotype may be better at coping with drought. G2, the more intermediate genotype in terms of biomass, recovered best from drought and flowered most frequently during recovery. These findings suggest these genotypes could fill different niches under variable environmental conditions, despite having high plasticity for photosynthesis, fluorescence, and leaf water potential. Subtle differences among genotypes may provide sufficient phenotypic variation by which a single population can evolve. Both plasticity in physiological response, as well as compensatory dynamics among different genotypes for growth and flowering could be important for explaining A. gerardii’s success under changing climate conditions.