Acclimatization to flooding of the herbaceous vine, Mikania scandens
1. Mikania scandens plants of three stem-length classes: small (< 4 cm), medium (4-10 cm) and large (> 10 cm), were transplanted into flooded or drained soil. After six weeks the relative growth rates (RGR), based on both dry weight and stem elongation, of the small plants under flooded conditions were 50% greater than those in drained soil. For the medium and large classes, the RGR values of the drained and flooded plants were similar. 2. Stem and root cross-sections revealed that flooded plants had two- and threefold respectively more aerenchyma tissue, with the amount in the stem decreasing in an acropetal direction. The stem surface contained stomata, not lenticels. The mean number of stem stomata was 267 and 57 for flooded and drained plants respectively on the 21 cm stem section above the water or soil line. 3. In root tissue ethanol and malic acid were below detectable concentrations, suggesting that anaerobic respiration was not an important component of metabolism under flooding. 4. Rather, M. scandens acclimatized anatomically with an increase in aerenchyma tissue and stem stomata, which would facilitate oxygen diffusion to the roots. Unlike other herbaceous, wetland species that use leaf stomata, the oxygen appeared to be derived from stem stomata. In this vine, insufficient oxygen diffusion down the long internodes probably necessitates use of stem stomata near the water-line. 5. These results indicate that M. scandens is flood-resistant, and may partially explain why it becomes a weed problem in flooded areas of Florida.