Foliar Permeability Among Twenty Species of the Bromeliaceae

The foliar uptake of calcium-45, zinc-65 and water through the leaf blade surfaces of diverse species of the Bromeliaceae was investigated using excised leaf discs or whole leaf blades. Zinc uptake ranged 50-fold among these surfaces; it was highest among four xeric tillandsias and relatively low in 16 bromelioid, pitcairnioid and mesic tillandsioid species. Relative rates of calcium uptake among 6 species paralleled the zinc data. Foliar absorption of water by partially desiccated leaf blades was slight or non- existent except in the four xerie tillandsias which exhibited high cation uptake. Species which have the greatest proportion of their leaf surfaces occupied by trichome stalks comprised of densely cytoplasmic cells showed the highest water, calcium and zinc uptake. Although all trichomes studied possess stalks ef living cells which lead into the mesophyll, the presence of these stalks is not always associated with high water, calcium and zinc permeability. This study supports theories that an enhanced foliar absorptive capacity exists in xeric tillandsioids and that this capacity may be facilitated by a dense layer of specialized, absorbing trichomes. The implications of foliar permeability to the origin and evolution of the Bromeliaceae and its subfamilies are discussed.