Latitudinal variation in the degree of crassulacean acid metabolism in Puya chilensis

Abstract

Crassulacean acid metabolism (CAM) is a photosynthetic pathway found in many plant species from arid and semiarid environments. Few studies aiming to characterise plant species as CAM or C3 account for inter-population differences in photosynthetic pathway, often relying on samples taken from herbarium material and/or a single plant or population. This may be especially problematic for species growing under contrasting climate conditions, as is the case for species with a wide geographic range. We used Puya chilensis, a species previously reported as CAM and C3, to study among-population variation in expression of the CAM pathway within its distribution range, which spans a significant climate gradient. We carried out a wide sampling scheme, including five populations and a combination of analytical methods (quantification of nocturnal acidification and stable isotope measurements). The study populations of P. chilensis encompass the entire latitudinal distribution range, from semi-arid to temperate oceanic climates. Our results indicate that CAM decreased with latitude. However, even in the southern (wetter) populations, where δ13C values were indicative of C3 metabolism, we found some nocturnal acidification. We stress the value of using two methods along with the use of samples from different populations, as this allows more reliable conclusions on the photosynthetic pathway for 'probable' CAM species that face varying climate conditions within their distribution ranges.

Photosynthetic pathways in Bromeliaceae: phylogenetic and ecological significance of CAM and C3based on carbon isotope ratios for 1893 species

“…. Nevertheless, there may be individual instances of polymorphic behaviour in photosynthetic performance, such as that seen in the Puya chilensis Molina complex (Schulte et al, 2010;Jabaily & Sytsma, 2013;Zizka et al, 2013), in which δ 13 C values have been recorded ranging between −16.3‰ (this study) and −24.8‰ (Quezada, Zotz & Gianoli, 2014;cf. Medina et al, 1977;Griffiths, 1984); such material would clearly be worthy of further investigation at both the taxonomic and ecophysiological levels.…”

Think tank: water relations of Bromeliaceae in their evolutionary context

“…It is important to note that extreme care should be taken when performing such analyses to use best practice in terms of model calibration and sampling methodology. Herrera et al, 2010;Quezada, Zotz & Gianoli, 2014). First, the putative phylogenetic relationships used in this analysis are not consistent with those supported by the most comprehensive molecular phylogenetic analyses.…”

“…The capacity for CAM-cycling may exist in bromeliad taxa currently considered as C 3 plants because of the difficulty of identifying such capacity in rapid screens of carbon isotope values. In another instance of intraspecific variability in CAM expression, CAM activity has been shown to vary with elevation in Puya chilensis Molina (Quezada et al, 2014). CAM-idling therefore cannot make a net contribution to the carbon balance of a plant.…”

“…In many cases, CAM-cycling andidling appear to be reversibly inducible, and drought-inducible CAM has been observed in some species such as the terrestrial Puya floccosa (Linden) E.Morren ex Mez (Herrera et al, 2010). In another instance of intraspecific variability in CAM expression, CAM activity has been shown to vary with elevation in Puya chilensis Molina (Quezada et al, 2014). There are many examples of CAM bromeliads in perhumid cloud forests, where the classical benefit of CAM in improving WUE is negated by the constantly low VPD.…”

“…Both Puya and Tillandsia L. are coded as CAM genera, whereas both are known to include many C 3 species and in Puya there are several intermediates (e.g. Herrera et al, 2010;Quezada, Zotz & Gianoli, 2014). A more rigorous analysis by Silvestro et al (2014) identified CAM as a driver of diversification in Bromelioideae, but it is too facile to assume this conclusion should apply across the whole family, in which 50% of extant species use C 3 photosynthesis only (Crayn et al, 2015).…”