Directional growth of a clonal bromeliad species i

Authors: Michelle C Sampaio Tatiana F Araújo Fabio R Scarano Josef F Stuefer

Publish Date: 2005/05/20

Volume: 18, Issue: 5-6, Pages: 429-442

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Abstract

Habitat selection by directional growth of plants has previously been investigated but field evidence for this phenomenon is extremely scarce In this study we demonstrate directional clonal growth in Aechmea nudicaulis a monocarpic perennial bromeliad native to spatially heterogeneous sandy coastal plains restinga in Brazil This habitat is characterized by a matrix of bare sand with interspersed vegetation islands Due to very high soil surface temperatures and other stress factors such as drought A nudicauliscan only germinate inside vegetation islands Nevertheless this species is very common on bare sand In this study we tested the hypothesis that clonal fragments occurring at the border and inside vegetation islands show habitat selection by growing preferentially towards the bare sand habitat ie away from the center of vegetation islandsWe randomly chose 116 clonal fragments in two distinct microenvironments inside vegetation islands and in the border area between bare sand and vegetation islands in the natural habitat of Anudicaulisand measured their growth direction in relation to the island center We measured the growth directions of entire clonal fragments defined as the line that connects the oldest and the youngest ramets of a clonal fragment as well as the growth direction of the youngest internode on each fragment the growth direction of the youngest ramet in relation to its parent ramet We used Monte Carlo simulations to test for deviations from randomness in the growth direction of clonal fragments and individual internodes The clonal fragments of Anudicaulis showed a significant tendency to grow away from the center of vegetation islands In other words the main growth direction of clonal fragments growing inside vegetation islands or at the border between bare sand and vegetation islands was preferentially directed towards bare sand environments Individual internodes at the border of vegetation islands also exhibited this tendency to grow towards the outside of vegetation islands but internodes growing inside vegetation islands did not show directional growth These results provide the first field evidence for habitat selection through directional growth of a clonal plant species

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