CAM plants: their importance in epiphyte communities and prospects with global change

Abstract

Background and scope: The epiphytic life form characterizes almost 10 % of all vascular plants. Defined by structural dependence throughout their life and their non-parasitic relationship with the host, the term epiphyte describes a heterogeneous and taxonomically diverse group of plants. This article reviews the importance of crassulacean acid metabolism (CAM) among epiphytes in current climatic conditions and explores the prospects under global change.

Results and conclusions: We question the view of a disproportionate importance of CAM among epiphytes and its role as a 'key innovation' for epiphytism but do identify ecological conditions in which epiphytic existence seems to be contingent on the presence of this photosynthetic pathway. Possibly divergent responses of CAM and C3 epiphytes to future changes in climate and land use are discussed with the help of experimental evidence, current distributional patterns and the results of several long-term descriptive community studies. The results and their interpretation aim to stimulate a fruitful discussion on the role of CAM in epiphytes in current climatic conditions and in altered climatic conditions in the future.

Keywords: Carbon isotopes; crassulacean acid metabolism; disturbance; dry forest; epiphytes; functional traits; germination; global change; key innovation; plant–water relationships.

Fig. 1.

Relative importance of crassulacean acid metabolism (CAM) in a vascular epiphyte community in the lowland forest of San Lorenzo (Panama) expressed as the proportion of species with CAM, the proportion of individuals with CAM and the contribution of these individuals to total biomass. For details, see Zotz (2004).

Fig. 2.

Temporal changes in the percentage of abundance and number of species of epiphytic C₃ species and species with crassulacean acid metabolism (CAM) in three different systems. Annona, epiphyte assemblages censused three times on Annona glabra trees growing along the shoreline of Barro Colorado Island (Einzmann et al., 2021); Pastures, epiphyte assemblages censused twice on pasture trees growing along a rainfall gradient in western Panama (Einzmann and Zotz, 2017); San Lorenzo, epiphyte assemblages censused twice on all trees within the San Lorenzo crane site (Mendieta-Leiva et al., 2022).