INTERACTIONS BETWEEN CYANOPHYTA AND GYPSUM PLATES, CHIHUAHUAN DESERT, SW TEXAS

Gypsum plates are a common occurrence in desert pavement environments. In the Chihuahuan Desert region of southwestern Texas the underside of these translucent plates are often colonized by a variety of microorganisms. Blue-green cyanophyta are the most prominent of these where they colonize highly embayed regions on the underside of the gypsum plates. This research is to determine if the pitting of these plates is the result of or aided by the organism(s) (active model) or if the cyanophyta simply colonize highly pitted and embayed portions of the gypsum plate (passive model). To test these hypotheses, samples of gypsum plates were collected from the Chihuahuan Desert – Christmas Mountains area in west Texas. These samples were cleaved to yield fresh (010) faces and the cleaved surfaces were imaged with an Environmental Scanning Electron Microscope (ESEM). A layer of epoxy will be used to mask portions of the of the cleavage surface during the ensuing experiments. The unmasked half of the surface will be inoculated with the living bacteria and cyanophyta collected from the embayed gypsum surfaces. The plates will then be inverted and set over BG 11 medium to ensure the bacteria’s growth. Heat lamps will be used to recreate desert temperatures. Bacteria- free samples will be used as controls to account for any inorganically derived dissolution of the surface during the experiment. After being allowed to grow for six weeks, the bacteria and the masking will be removed and the cleavage surface imaged (reflected light microscopy and ESEM) to compare the protected portions with the inoculated portions of the surface. Comparison of these surfaces with the control groups should provide us with data on the role that the bacteria/cyanophyta play (if any) in the modification of the mineral interface. The results from these experiments will then be compared to textures and colonization patterns observed on the natural gypsum plate surfaces to see if direct comparisons can be made.