Thigmomorphogenic Responses of Epiphytic Bromeliads to Mechanical Perturbation
Abstract Vascular epiphytes represent almost 10% of all terrestrial plant diversity. Despite their growing sites exposed to frequent extensive storms, nothing is known about how external mechanical perturbations by wind affects epiphytes’ growth and development. Therefore, this study investigated the effect of such mechanical stress on the growth rate and morphology of epiphytes. Juvenile plants of two species of bromeliads, grown in the greenhouse, were subjected to varying degrees of mechanical stress – Permanent displacement, tilting and mechanical flexing. ANOVAs were used to test possible treatment effects on growth, root-shoot ratio, root diameter, and leeward-windward root area ratio. Contrary to previous studies on herbaceous plants, these bromeliads showed little to no change in root and shoot properties in either species. Although the root-shoot ratio increased in disturbed Guzmania lingulata plants (Tukey HSD, p < 0.001), it was not observed in Vriesea sp. Treatment effects on growth were inconsistent: stress effect on growth was significant only in the first three months of the experiment (padj < 0.05) in G. lingulata, while none of the stress treatments resulted in negative growth in Vriesea sp. All disturbed plants showed some degree of curvature on their stems and leaves against the area of stress to obtain an upright position. This was probably related to the maintenance of a functional tank. This study provided quantitative and qualitative data to understand thigmomorphogenic responses of bromeliads to mechanical stress. Future studies could include field surveys to quantify on-site wind stress and the corresponding morphological changes in vascular epiphytes.