STOMATAL CHARACTERISTICS, CONDUCTANCE RATIOS, AND DROUGHT-INDUCED LEAF MODIFICATIONS OF SEMIARID GRASSLAND SPECIES

Seventeen greenhouse-grown grasses from the Nebraska Sandhills region were surveyed for foliar stomatal density and distribution, closed gua rd cell lengths, open stomatal apertures, and surface characteristics (using scanning electron microscopy), surface conductance (using a ste ady-state porometer), and drought-induced leaf modifications. Leaves o f C-3 species exhibited a proclivity toward being amphistomatic or hyp erstomatic, while C-4 species tended to be more hypostomatic. Leaf mod ification, when it occurred, resulted in the enshrouding of the adaxia l surface. Conductance data showed functional amphistomaty in most spe cies, revealing differential functioning of adaxial and abaxial stomat a. Conductance patterns were not closely related to stomatal aperture per unit area leaf surface or to stomatal distribution patterns. Lower ed adaxial: abaxial conductance ratios, increased stomatal density, re duced stomatal size, and less drought-induced leaf modification were s een in C-4 grasses as compared with C-3 grasses. C-3 range and C-3 mea dow species did not differ in conductance ratios, density ratios, or s tomatal size, although meadow species exhibited much greater drought-i nduced leaf modification. Postulations involving correlation of adaxia l: abaxial conductance ratios to stomatal distribution patterns, and a ssumptions of stomatal distribution based upon habitat and/or photosyn thetic pathway may be erroneous. These characteristics may be of limit ed usefulness as morphological indicators in the search for drought-to lerant ecotypes of prairie grasses.