INTERNAL GAS-TRANSPORT IN TYPHA-LATIFOLIA L AND TYPHA-ANGUSTIFOLIA L .2. CONVECTIVE THROUGHFLOW PATHWAYS AND ECOLOGICAL SIGNIFICANCE

The gas flow pathways within Typha latifolia L. and Typha angustifolia L. were evaluated by studying the internal pressurization and convective flow through individual leaves and the internal resistances to gas flow within the plants. Air enters the middle-aged leaves against a small pressure gradient by humidity-induced pressurization, is convected down the lacunae of the leaves to the rhizome, and from there is vented back to the atmosphere, through old or damaged leaves or through horizontal rhizomes to other shoots. A model was developed to analyze the gas flow pattern within the plants under different conditions. The analysis showed that the throughflow pattern is dynamic: leaves can be influx leaves under a certain set of conditions and efflux leaves under different conditions. The specific internal resistance to gas flow was generally low in leaves (less than 1 Pa s mm(-2)) and rhizomes (3 Pa s mm(-2)), and somewhat higher in junctions between leaves and rhizome (5-14 Pa a mm(-2)). T. angustifolia generally produced a greater leaf area specific convective flow rate (up to 31 mu l min(-1) cm(-2)) than T. latifolia (up to 11 mu l min(-1) cm(-2)). This greater ventilation capacity of T. angustifolia may be significant for its ability to grow in deeper water, and may contribute to the explanation of the depth distribution of the two species.