Local adaptation, plasticity and physiological stress tolerance among five perennial grasses

Background/Question/Methods

Identifying physiological differences among species locally-adapted to natural hydrological variation is important for predicting changes in plant performance under future climatic conditions. Therefore, our objectives were to (1) identify differences in physiological traits among perennial grasses locally adapted across geographically separated sites and to different hydrological conditions within sites, (2) evaluate differences in morphological plasticity between individuals in the field and in a greenhouse setting, and (3) compare physiological responses to increasingly severe water limitation among individuals. Leaf samples and rhizomes of five perennial grasses (Andropogon gerardii, Sorghastrum nutans, Schizachryium scoparium, Dichanthelium oligosanthes, and Koleria macranantha) were collected from three topographic locations (uplands, mid-slopes, and lowlands) across six geographically separated locations in Kansas and Oklahoma, USA (Konza Prairie, Ninnescah, Oklahoma Tallgrass Prairie Preserve, Ross, NPS Tallgrass Prairie Preserve, Welda). Rhizomes were planted in a common garden at Kansas State University and plants were grown under well-watered conditions. Key functional traits (gas exchange physiology, stomatal density, aboveground productivity) were measured under these optimal conditions. Additionally, stomatal density was measured in leaves collected from individuals grown under field conditions. Finally, gas exchange physiology was measured periodically in individuals subjected to a dry-down period to identify differences in tolerance to extreme water stress.

Results/Conclusions

We observed significant differences in physiology, stomatal density and productivity among species and geographically separated locations. For example, a significant species x location interaction indicated that aboveground biomass was greatest in S. nutans and K. macranantha collected from Ninnescah and in A. gerardii and S. scoparium collected from Welda (p < 0.05). Additionally, a significant species x location interaction indicated that photosynthetic rates were significantly higher in S. nutans than other species, but only in plants collected from Ninnescah, Oklahoma and Welda (p < 0.05). Conversely, K. macranantha had significantly higher photosynthetic rates in plants collected at Konza Prairie (p < 0.05). There were no significant differences in physiology among topographic positions within sites. Difference in physiology also decreased among species and locations as water-stress became increasingly severe (p > 0.05). Finally, stomatal density varied significantly between D. oligonsanthes leaves collected in the field and grown in the garden, but the magnitude of this difference varied among location of origin (p < 0.05). These results provide strong evidence of local adaptation among sites within similar biomes and overall morphological plasticity in response to resource availability, but this trait variability may not translate to differences in tolerance to extreme water limitation.