Hydraulics link leaf shape and environmental niche in terrestrial bromeliads

Abstract

Terrestrial species of the megadiverse bromeliad family display a wide variety of leaf shapes, many of which have evolved convergently in different lineages. Here, I examine the links between leaf shape, venation architecture, hydraulic function, and bioclimatic relations in two bromeliad groups displaying diverse leaf shapes, the genus Pitcairnia (Pitcairnioideae) and the terrestrial grade of the Bromelioideae subfamily. Leaf shapes with broader leaf blades, notably petiolate and lanceolate morphologies, tend to show wider vein spacing, which is associated with reduced hydraulic capacity and higher hydraulic vulnerability. In turn, these leaf shapes tend to occur in species restricted to moist, aseasonal environments, suggesting that hydraulic function is an important mediator of the relationship between leaf shape and bromeliad environmental niches. This network of trait-trait and trait-environment relationships may have been of profound important in the ecological and evolutionary diversification of the bromeliads. Similar structure-function principles are likely to apply in other tropical herbaceous monocots, which are of great ecological importance but generally neglected in plant hydraulic research.

Geography, environment and organismal traits in the diversification of a major tropical herbaceous angiosperm radiation

“…Variation in the width of hydrological habitat ranges of C 3 mesic terrestrials tended to align more closely with loadings for variables related to overall moisture, indicating the pre-eminent importance of adequate (often high) water supply for these species. The apparently greater importance of P dry in limiting hydrological habitat range in C 3 and CAM succulent terrestrial bromeliads is consistent with the hypothesis that succulent plants tend to occur within relatively narrow ranges of dry-season precipitation ( Ellenberg 1981 ; Ogburn and Edwards 2010 ; Males 2017 ).…”

“…This diversity could relate to the origin of root vessels in Pitcairnia , which presumably facilitate more efficient root-mediated water uptake ( Tomlinson 1969 ; Males 2016 ), and the greater evolutionary lability in leaf form seen in Pitcairnia and Fosterella . It is perhaps significant that among Pitcairnia spp., many species occurring in high-moisture environments display broad, (pseudo-)petiolate leaf blades, whereas those from the driest and most seasonal environments frequently display highly reduced, sometimes spinose, linear leaf blades ( Males 2017 ). Similarly, convergent cases of petiolate leaf morphology in the genera Cryptanthus and Disteganthus appeared to be associated with high levels of moisture, and the same is probably true for the strongly petiolate Bromelia scarlatina , for which sufficient distributional data were not available for analysis but which is closely related to the B. tubulosa , which was associated with higher moisture levels than any of its congeners.…”

“… Cruz et al (2017) note that multiple accessions for the petiolate species Cryptanthus beuckeri were not recovered as monophyletic in their phylogenetic analyses, suggesting that petiolate leaves may have arisen several times within that genus and underscoring the intriguingly recurrent nature of this trait in the bromeliads. Leaf shape is intimately associated with tank-mediated water trapping and foliar venation architecture, and therefore varies in tandem with leaf hydraulic properties and responses to water deficit ( Males 2017 ). The more xeromorphic leaf morphoanatomy displayed by Fosterella spp.…”

Embolism resistance in petioles and leaflets of palms

“…Embolism resistance in monocots is known mostly for species in the grass family (e.g. Lens et al, 2016) and more recently, bromeliads (Males, 2017). Embolism resistance in the palm family has been relatively poorly studied (though see Renninger and Phillips, 2011).…”

Transcriptional foliar profile of the C3-CAM bromeliad Guzmania monostachia

“…The leaf blade of tank bromeliads present morpho-functional heterogeneity with a gradient of specializations from the basal to the apical portions [3–7, 13–15], but in a few cases the morpho-physiological aspects are systematically investigated in relation to their functional significance [16] and, to our knowledge, nothing is known about the genes that could play a key role in each leaf portion. In order to provide an overview of the transcriptional profile of the leaf blade of G .…”