Does Egypt Represent an Ecological Limit to Desiccation Tolerant Plants?

Abstract

A search of arid areas adjacent to the Nile in Egypt revealed a notable lack of desiccation tolerant vascular plants on ecological sites on which they would be abundant in Kenya and further south in Africa. Relative water contents (RWC); the water content of the tissue as a percentage of its water content at full turgor; were estimated after the tissue had been floated on water for 24h and then dried in a 70° C oven to avoid errors due to decomposition at higher temperatures. Viability of the rehydrated tissue was judged from tests of the retention of semipermeability of the cell membranes and by formation of chlorophyll in non-chlorophyllous tissue in the light. Possible causes of their apparent absence from suitable sites in the Aswan-Qena area are discussed. We attribute their absence to time durations between effective rainfall events that exceed the longevity of resurrection plants while in an air-dry anabiotic condition. This is, to our knowledge, the first report of an aridity-related factor that may present an ecological limit to fully desiccation-tolerant plants.