In Situ Accumulation of CaOx Crystals in Leaves and Its Relationship with Anatomy and Gas Exchange.

The accumulation of crystal calcium oxalate (CaOx) in plants is linked to a type of stress-induced photosynthesis termed 'alarm photosynthesis', serving as a carbon reservoir when carbon dioxide (CO) exchange is constrained. is an extremophyte found from southern Mexico to Antarctica, which thrives in high-altitude Andean regions. Growing under common garden conditions, from different latitudinal provenances display significant variations in CaOx crystal accumulation. This raises the following questions: are these differences maintained under natural conditions? And is the CaOx accumulation related to mesophyll conductance (g) and net photosynthesis (A) performed in situ? It is hypothesized that in provenances with lower g, will exhibit an increase in the use of CaOx crystals, resulting in reduced crystal leaf abundance. Plants from Central Chile (33°), Patagonia (51°), and Antarctica (62°) were measured in situ and sampled to determine gas exchange and CaOx crystal accumulation, respectively. Both A and g decrease towards higher latitudes, correlating with increases in leaf mass area and leaf density. The crystal accumulation decreases at higher latitudes, correlating positively with A and g. Thus, in provenances where environmental conditions induce more xeric traits, the CO availability for photosynthesis decreases, making the activation of alarm photosynthesis feasible as an internal source of CO.