CAM photosynthesis in desert blooming Cistanthe of the Atacama, Chile

When plants of the Atacama desert undergo episodic blooms, among the most prominent are succulent-leaved Cistanthe (Montiaceae). We demonstrate that two Cistanthe species, the perennial Cistanthe sp. aff. crassifolia and the annual/biannual Cistanthe sp. aff. longiscapa, can exhibit net CO2 uptake and leaf acidification patterns typical of crassulacean acid metabolism (CAM). In C. sp. aff. crassifolia leaves, CAM expression was facultative. CAM-type nocturnal net CO2 uptake and acid accumulation occurred in drought-stressed but not in well-watered plants. By contrast, CAM expression in C. sp. aff. longiscapa was largely constitutive. Nocturnal acid accumulation was present in leaves of well-watered and in droughted plants. Following water-deficit stress, net nocturnal CO2 uptake was induced and the level of acid accumulated increased. Neither nocturnal CO2 uptake nor acid accumulation was reduced when the plants were re-watered. delta C-13 values of a further nine field-collected Cistanthe species are consistent with a contribution of CAM to their carbon pools. In the Portulacinae, a suborder with eight CAM-containing families, Cistanthe becomes the sixth genus with CAM within the family Montiaceae, and it is likely that the ancestor of all Portulacineae also possessed CAM photosynthesis. In the stochastic rainfall landscape of the Atacama, carbon uptake in the dark is a water-use efficient mechanism that increases the carbon pool available for seed production or dormancy. The next rain event may be years away.

Automated summary

In the Atacama desert, plants of the Cistanthe genus exhibit features of crassulacean acid metabolism (CAM) during episodic blooms, with CAM expression being facultative in some species and largely constitutive in others. This water-use efficient mechanism of dark carbon uptake increases carbon pools available for seed production or dormancy, especially important in the arid, stochastic rainfall landscape of the desert where the next rain event may be years away. Additionally, evidence from field-collected Cistanthe species suggests a contribution of CAM to their carbon pools.