Crassulacean acid metabolism photosynthesis in Bromeliaceae: an evolutionary key innovation

Abstract

Crassulacean acid metabolism (CAM) is a photosynthetic pathway that significantly increases water use efficiency in plants. It has been proposed that CAM photosynthesis, which evolved from the ancestral C3 pathway, has played a role in the diversification of some prominent plant groups because it may have allowed them to colonize and successfully spread into arid or semi-arid environments. However, the hypothesis that CAM photosynthesis constitutes an evolutionary key innovation, thereby enhancing diversification rates of the clades possessing it, has not been evaluated quantitatively. We tested whether CAM photosynthesis is a key innovation in the Bromeliaceae, a large and highly diversified plant family that has successfully colonized arid environments. We identified five pairs of sister groups with and without the CAM feature, including 31 genera and over 2000 species. In all five cases, the clades with CAM photosynthesis were more diverse than their C3 counterparts. We provide quantitative evidence that the evolution of CAM photosynthesis is significantly associated with increased diversification in Bromeliaceae and thus constitutes an evolutionary key innovation. We also found preliminary evidence of an association between the CAM pathway and growth habit in bromeliads, with terrestrial species being more likely to show CAM photosynthesis than epiphytic species. To our knowledge, this is the first case of a physiological attribute shown to be a key innovation in plants.

Screening of Maize Genotypes for Drought Tolerance Related Trait Variability

“…Under drought root biomass at bottom was highest in GM-6 (0.414 g) followed by C-15 (0.395 g) and KG-2 (0.392 g) and was lowest in PM-5 (0.124 g), while as under irrigated conditions it was highest in KG-1 (0.399 g) followed by PM-5 (0.273 g) and KG-2 (0.256 g) and was lowest in PM Chari-6 (0.064 g). Root: shoot ratio increases dramatically under drought conditions suggesting that functional responses to reduced soil moisture primarily occur through increased growth of roots, as has been shown suggested by Quezada and Gianoli (2010). Similarly, Huang et al, (2013) also reported that deficiencies of soil water resulted in high root: shoot ratio.…”

CAM Photosynthesis in Bromeliads and Agaves: What Can We Learn from These Plants?

“…Without the tank, atmospheric bromeliads (Type IV) have to perform CAM or they will not survive. Therefore, the presence of the tank in some epiphytic bromeliads could be the reason why a clear correlation between CAM and epiphytism was not found in Bromeliaceae, different from other families with epiphytic species [4,68,80].…”

“…In contrast to the Orchidaceae family, however, among bromeliads a strong correlation was not found between the occurrence of CAM and epiphytism [68]. In fact, a more recent work suggested that CAM could be more common in terrestrial, rather than epiphytic, bromeliad species [80]. Although very enlightening, these studies focused on the phylogeny and took into account only whether the plants were epiphytes or not.…”

Adaptive radiation, correlated and contingent evolution, and net species diversification in Bromeliaceae

“…Claims by Quezada and Gianoli (2011) that CAM is associated with higher diversification rates in bromeliads are based on their incorrect identification of four of five sistergroup comparisons they employed.…”