Meisner & Zotz 2012 (Conference Paper) Heteroblasty

Prevalence and gunctional relevance of Heteroblasty in Epiphytic Bromeliads.

Author(s):—K. Meisner & G. Zotz

Corresponding email:—gerhard.zotz@unioldenburg.de

Publication:— (2012).

Abstract:—Heteroblasty is characterized by abrupt changes in the ontogeny of plants, from a young leaf form (linear leaves) to broad leaves, where overlapping bases form a water-impounding tank. We investigated this phenomenon in epiphytic members of the subfamily Tillandsioideae (Bromeliaceae). Similar prevalence of heteroblasty in local bromeliad floras in a seasonal lowland site and a wet montane site in Panama (60-75% of all species) calls into question the generally held notion that heteroblasty is exclusively an adaptation to drought. We suggest that atmospheric forms may also increase light capture in the understorey by reducing self-shading. With a suite of descriptive and experimental approaches we analyzed the functional consequences of this ontogenetic change (morphology: foliar trichomes, stomatal density, anatomy: hydrenchyma, chlorenchyma and leaf thickness, tank capacity and nutrient uptake, in situ relative growth rates). In most cases, the abrupt change in form was not associated with a sudden change in function, the exception being nutrient uptake rates, which were significantly higher in smaller, atmospheric plants compared to conspecifics with a tank. Heteroblasty in bromeliads is thus a much more complicated phenomenon than currently acknowledged. Although our study provides important insights into the ecological physiology of heteroblasty in Bromeliaceae, we are far from a full understanding of its functional significance.