Nine populations were selected that represent three different degrees of aridity. Climate data for each collection site will be gathered using a program called Climate WNA. These data will be used to group each population into one of three groups according to an aridity index. This aridity index is calculated using the ratio of mean annual precipitation (P) and mean annual potential evapotranspiration (PET) and is currently used by the United Nations Environment Programme (2006) to categorize arid regions.

Twenty-four replicates from each collection site were planted in a randomized block design and grown in a growth chamber set to 61 degrees F with diurnal lighting in twelve hour cycles. Plants will be grown under optimal conditions until leaves develop that are conducive to stomatal measurements (approx. 3 weeks).

The central portion of the longest leaf from each plant will be coated in nail varnish on both the adaxial and abaxial surfaces. Once dry, the varnish will be peeled away from the grass blade and mounted onto microscope slides.

Stomates will be counted manually using a compound microscope at 200X magnification. All stomates within a predefined area will be counted at three different locations along the length of the midrib and averaged.

References:

United Nations Environment Programme. 2006. “The Desert Biome: A Global Perspective.” Global Deserts Outlook chapter 1. http://www.unep.org/geo/gdoutlook/016.asp.