In addition, other nutrients are scarce in these infertile habitats, and the CAM pathway potentially could enhance nitrogen-use efficiency (Griffiths, 1989; Robe & Griffiths, 1994).
In the lacustrine habitat, the CAM pathway contributes about 50% of the total annual carbon gain, largely through the extension of the carbon assimilation period (Boston & Adams, 1986).
As the dry season approaches, and these aerial plants are exposed to increasing aridity, they do not regain the CAM pathway.
Table I), which, of course, does not preclude presence of the CAM pathway.
These observations do not conclusively demonstrate absence of the CAM pathway, as even well-recognized terrestrial CAM plants utilize some portion of dark-fixed carbon for non-autotrophic metabolism (Luttge, 1988).
Two terrestrial annual species in Disporocarpa lack CAM and CAM can not be induced (Table V), and these are perhaps the only members of the family completely lacking the CAM pathway (cf.