A potentially important seedling trait is stomatal density. Woodward (1987) found that stomatal density and distribution may affect gas exchange and associated relationships with environmental factors such as light, CO2, and water status.

Xu and Zhou (2008) found that stomatal density increased, but the number of stomata per-leaf decreased with water stress, and this change in stomatal density was correlated to changes in specific leaf area water use efficiency in another species of perennial grass.

Stomatal density may therefore be an important adaptive trait for bluebunch wheatgrass in the Great Basin. We aim to fill the knowledge gap surrounding seedling stomatal density in bluebunch wheatgrass to determine whether adaptation to climate exists for this trait.

Stomate Study

Hypothesis & objective:

We hypothesize that stomatal density is a driver of drought tolerance in young bluebunch wheatgrass plants and that the variability in this trait is caused by natural selection and local adaptation. Our objective is to determine the range of variability in stomatal density in populations along an aridity gradient and to tie this trait to selection through climate. Using an exploratory approach, we will measure stomatal densities from young plants (grown from seed-sources along an aridity gradient) and determine their relationship to climate in terms of aridity.

Expected results and interpretations:

We predict that there is a negative correlation between stomatal density and aridity. If this prediction is supported, then there is evidence that natural selection has reduced stomatal density in arid environments as compared to less arid environments. If this prediction is not supported, then we must conclude that stomatal density does not change in relation to aridity.

References:

Woodward, F. I. 1987. “Stomatal Numbers Are Sensitive to Increases in CO2 from Pre-Industrial Levels.” Nature 327 (6123): 617–18. doi:10.1038/327617a0.

Xu, Zhenzhu, and Guangsheng Zhou. 2008. “Responses of Leaf Stomatal Density to Water Status and Its Relationship with Photosynthesis in a Grass.” Journal of Experimental Botany 59 (12): 3317–25. doi:10.1093/jxb/ern185.