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Trade‐offs tip toward litter trapping: Insights from a little‐known Panamanian cloud‐forest treelet

Each plant's development unfolds along many trade‐off axes. One common trade‐off is engendered by the differential allocation of tissues to harvest essential resources from the surrounding environment. Generally, photosynthetic leaves capture light energy and carbon dioxide, whereas roots take up water and mineral nutrients.

Since these specialized functions are usually performed in separate realms – above‐ and belowground, respectively – plants must differentially invest in the construction of above‐ versus belowground organs to meet their resource requirements. Furthermore, plants tend to develop leaf and root morphology and placement to make efficient resource harvests. Accordingly, design trade‐offs also shape plants’ adaptive architectures. In light of these broad trade‐offs, Quadrella antonensis (Woodson) Iltis & Cornejo (Capparaceae), a shrub or small tree restricted to the understory of a few montane cloud forests in Panama, presents a paradox: why does it appear to be so clearly adapted to capture and retain fine debris in “trash baskets” when this necessarily reduces light absorption and photosynthesis?

The most distinctive features of Q. antonensis are those that inspired its common names (basurera, trash‐basket plant) – clusters of large leaves tightly spiraled along stem and branch tips. These leaf‐cluster baskets collect fine litter that falls from overtopping vegetation. It is impossible for the leaves of the plant to be arranged in a way that maximizes light and litter capture simultaneously. An alteration in the leaf arrangement to avoid self‐shading or shading by captured litter would render the arrangement relatively ineffective at litter capture. To cluster, overlap, or otherwise arrange leaves to effectively capture litter unavoidably reduces light capture efficiency in an already shady forest understory.

Why would natural selection favor a plant architecture that partially obscures its necessary photosynthetic surfaces? In other words, is there a counterbalancing advantage to litter trapping that overcomes the obvious carbon‐balance costs? Here, we begin to address this question using Q. antonensis.

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Publication Date: 11/20/2020
Photo credits: Kyle Harms & Jim Dalling
Editor: Drs. Harms, Dalling & Sánchez de Stapf