Research on Crassulacean Acid Metabolism (CAM)

Plants are able to produce sugar from water and carbon dioxide (CO₂). This process is called photosynthesis (from Greek φως: light) because the energy required for it comes from sunlight. Most plants take up CO₂ from the atmosphere during the day and can use it to produce sugar immediately when the sun shines. To absorb CO₂, plants need to open tiny pores (stomata) on their leaves. Water also evaporates through these pores, which is not a problem if water is available from the soil. However, when drought sets in and the plant conserves water, it closes its stomata and can no longer take up CO₂. In the course of evolution, around 6.5% of all land plants have developed a mechanism that can solve this problem: Crassulacean Acid Metabolism (CAM).

Photosynthesis by night

CAM involves nocturnal CO₂ uptake from the air, at a time when the atmosphere is cooler and more humid than during the day. Carbon dioxide is then stored as malic acid in the cells until the next day, causing the leaves or shoots of the plant to become increasingly acidic over the course of the night. During the day, CO₂ derived from the malic acid is available for photosynthesis and already inside the plant. The plant can therefore close its stomata and thus save water and still produce sugar. The malic acid is broken down throughout the day so that the next acidification process can begin in the evening. This is where the complicated name of this special metabolism comes from: In 1815, the German botanist Benjamin Heyne tasted the sour taste of Crassulaceae leaves in the morning and their less sour (bitter) taste in the evening.

Researchers at the Botanical Garden Munich-Nymphenburg investigate CAM and are particularly interested in the ecology and evolution of this mechanism across the plant tree of life. CAM does not only occur in Crassulaceae but has evolved independently at least 66 times in 38 different plant families. These families have usually also evolved succulence, i.e., the ability to survive long periods of drought by storing water inside their body.

Research on the genus Aeonium

The genus Aeonium (Canary Island houseleeks) is particularly suitable for research into the diversity of CAM. Aeonium is represented by a total of 41 species on the Canary Islands from where it has colonized Madeira, Cape Verde and the African continent. By migrating from island to island and specializing in different humid or dry habitats, CAM was repeatedly adapted to the environmental conditions but has never been completely lost. In addition, our research has shown that species that rely heavily on CAM also have particularly effective protection against desiccation by adapting their wax-covered surface, the cuticle.