干旱区生态环境知识资源中心

The distribution and life cycle of Welwitschia mirabilis are briefly outlined before a detailed description of the germination and establishment of seedlings is given. Inorganic ions, organic acids, and proline occur in high amounts in a Welwitschia leaf and exhibit typical distribution patterns. Water relations of Welwitschia, growing at three contrasting habitats of the Namib, are presented in relation to water availability in the soil and climatic constraints. A positive relationship between predawn leaf water potential and leaf growth was found. CO2 uptake and water loss measured at the three habitats showed a negligible WUE over 24 h for a whole plant. In the driest habitat, the CO2 balance of the entire leaf was negative over a period of 150 days but the leaf still grew. Utilizable biomass in the leaf was found to be high, allowing the leaf to survive even with a negative CO2 balance for at least 1 year provided water is available.