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Survival Strategy in the Wetland Sedge Carex brevicuspis (Cyperaceae) in Response to Flood and Drought: Avoidance or Tolerance?

Survival strategies of plants to adapt to environmental stress include avoidance and tolerance. These strategies were investigated in the wetland sedge Carex brevicuspis (Cyperaceae) to determine the plasticity of its response to flood and drought. Individual plants were grown in PVC tubes and subjected to five water levels relative to soil surface: -40 cm, -20 cm, 0 cm, +20 cm, and +40 cm. After 60 days, plants were harvested and their biomass accumulation, number of leaves (a measure of growth), root and shoot elongation, aerenchyma formation (avoidance strategy), amount of malondialdehyde (MDA), amount of water-soluble carbohydrates (WSC), alcohol dehydrogenase (ADH) activity, amount of proline (tolerance strategy), and membrane permeability (a measure of degree of injury) were assessed. Relatively high amounts of MDA and proline and a high level of ADH activity, combined with relatively low aerenchyma area, short leaves, and low amount of WSC in the +20 cm and +40 cm treatments indicated that C. brevicuspis responded to floods with tolerance. A significant root elongation and WSC accumulation in the -20 cm treatment indicated that the species responded with high levels of avoidance to mild drought. High amounts of MDA and proline combined with relatively short roots and a low amount of WSC in the -40 cm treatment indicated a high tolerance strategy under severe drought. Overall, C. brevicuspis responded with tolerance to flood and adopted avoidance to mild drought, and it went back to tolerance under severe drought.