PARENT SESSION
Poster Session #33: Rare, Threatened, and Endangered Species.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

An ecophysiological study of Astragalus bibullatus (Fabaceae).

Baskauf, Carol^*,1, Reppuhn, Dustine², ¹ Austin Peay State University, Clarksville, TN² University of Tennessee-Knoxville, Knoxville, TN

ABSTRACT- The endangered cedar glade endemic Astragalus bibullatus grows best under medium to high light and moisture conditions, although it can survive under quite dry soil conditions. Thus, it appears well-adapted to its open cedar glade habitat and able to thrive even in a limited amount of shading. Dense shade and very low soil moisture strongly inhibit growth. Surprisingly, this rare species demonstrated better growth and survival than its widespread prairie congener A. crassicarpus. After 2 months of growth, A. bibullatus averaged more than 3 times as many leaves as A. crassicarpus and 2.5 times as much dry biomass. Although leaf number and biomass production were uniformly low for both species under conditions of low light and/or low moisture, the gap between the species widened as light and/or moisture levels increased. A. crassicarpus grew best with medium light levels and high soil moisture. Photoysnthesis levels for both Astragalus species are somewhat low, as is true for many other slowly growing stress-tolerant species, and rates are inhibited by high temperatures. Water potential decreases as soil dries, but A. crassicarpus averaged lower water potentials than did A. bibullatus. Seedlings of both species suffered extremely high mortality rates due to stem rot caused by the fungus Alternaria. This fungus occurs on field-collected pods and seeds, but its importance as a mortality factor in the field is not known.

KEY WORDS: Astragalus bibullatus, rare species, ecophysiology, cedar glade