Poster: Ecophysiology

Abs # 54: The ecophysiological consequences of the underground growth habit of "Living Stones" (Lithops species)

Presenter:	Martin, Craig E., ecophys@ku.edu
Authors	Martin, Craig E. (A)   Egbert, Kathryn  (A)   King, Samantha  (A)   Zupancic, Amity  (A)
Affiliations:	(A): Dept. of Ecology & Evolutionary Biology, University of Kansas
Web Site:	http://www.ku.edu/~eeb

Species of Lithops grow in extremely arid regions of southern Africa. The plant body comprises two succulent leaves that grow underground, with only the flat, uppermost surfaces of the leaves exposed to light and the atmosphere. These surfaces are typically flush with the surface of the ground and, in some species of Lithops, are translucent and have been termed “windows.” The subtending water-storage parenchyma is clear; chlorophyll is found only along the outermost edges of the succulent leaves. It has long been assumed that the “windows” allow light to penetrate deep into the leaves, allowing photosynthesis by the chlorophyllous tissue. Surprisingly, previous work from our lab indicated that preventing the bulk of light from entering the leaves effects increases in photosynthetic activity of the plants, instead of the expected decreases in activity. These experiments were recently repeated using species of Lithops having pigmented, less translucent windows. In contrast with the previous findings, plant photosynthetic activity declined when the windows were obscured. Thus, the physiological impacts of the penetration of light into the leaf interior via leaf windows is dependent on the opacity of the window. In another investigation of the ecophysiological consequences of the underground growth habit of species of Lithops, rates of CO₂ exchange and water vapor loss were compared in control plants growing underground and in experimental plants with leaves fully exposed out of the soil. Rates of both photosynthesis and water loss were substantially elevated in the plants with exposed leaves, relative to those in the soil. Thus, the underground growth habit saves a considerable amount of water for these plants but also results in reduced rates of carbon uptake.