1 - A rich ecosystem of lichen crusts on a rock surface.

Desiccation tolerant plants can lose all water but resume activity at when re-wet: algae, lichens, and mosses.

2 - Sempervivum montanum (Crassulaceae)

3 - Trichocereus pasacana (Cactaceae) (3000 m, NW-Argentinean Andes)

Dry mountain habitats permit slow growing succulents to thrive. Some stay small such as Sempervivum montanum (Fig. 2), others, such as this giant cactus at 3000 m in the Argentinean Andes (Fig. 3), get very big. Both have in common

• water storage

• CAM metabolism

What is CAM (Crassulaceaen acid metabolism)? CAM plants are able to absorb CO₂ during the night (open stomata, little vapour loss) and store it as carbonic acid in their cell sap. During the day, the stored CO₂ is used for photosynthesis while stomata remain closed.

4 - Measurement of surface water loss.

Cushion plants have their "private" compost heap which stores a lot of water and nutrients (Fig. 4). Such compact cushions are often found on poor, underdeveloped substrates.

29 August 2011
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