The influence of stomatal morphology on gas-exchange processes of native and invasive mid-Atlantic tree species

Background/Question/Methods

This study measured the effect of stomatal structure on gas-exchange processes in three different ozone (O₃) concentrations (20ppb, 80ppb, 160ppb) and compared the stomata morphologies across eight native and five invasive tree species from the mid-Atlantic region.  Two leaves from 103 trees were measured under 400x magnification after being prepared and stained with safranin O dye. 

The goals of this study addressed the questions surrounding the relationship of stomatal morphology to gas-exchange processes, including:

1. Observing if stomatal morphology varies among tree species. 
2. Determining the effects of stomatal morphological differences on gas-exchange.
3. Determining if the influence of stomatal morphology on gas-exchange varies by species.
4. Distinguishing whether invasive and native species exhibit different stomatal morphologies. 

Results/Conclusions

Significant variations in stomatal complex size, guard cell width, number of contact cells, and stomatal density were measured across species.  The stomatal complex size, guard cell width, guard cell length, and number of contact cells were all positively correlated to each other.  Novel correlations between stomatal type and guard cell width, number of contact cells, and stomatal complex size were discovered.  No significant morphological differences were found between native and invasive species groups showing that stomatal traits are not a means of competitive advantage and successful invasion.  Stomatal characteristics were found to correlate to ozone uptake, cumulative ozone uptake, and net photosynthesis, but not stomatal conductance.  Cumulative ozone uptake at the medium ozone treatment departed from other trends and suggests protective mechanisms in trees to avoid ozone uptake.  When looking at the high ozone treatment in comparison to the low ozone treatment, the traits that contributed to net photosynthesis changed from stomatal density at the low treatment to guard cell width and stomatal complex size at the high treatment.  This switch could be means for a new competitive advantage in environments where ozone levels are increasing.  Individual tree species also exhibited variation in physical stomatal characteristics and their strength of influence on gas-exchange processes.