Flow characteristics and internal pressure profiles in leaves of the Typha domingensis

Abstract

The resistance to convective flow was measured in excised leaves of Typha domingensis where the internal pressure was self-generated ('intact') or artificially supplied by pumping gas through the leaf tip ('cut'). The resistance in intact material was 74.0% of the actual resistances as measured in 'cut' treatment (4.2+/-2.0 compared with 5.6+/-2.3MPasm-3) which was greater than the expected mean of 50%. Taking into account changes in the surface area along the leaf, this equates with a value of 59.4% of the total surface area starting at the leaf base suggesting that gas is preferentially entering the distal portion of the leaf. The resistance was also measured in intact material which was progressively inundated. As inundation increased, so too did the apparent resistance from 0.4MPasm-3 when the leaf was fully exposed to 4.8MPasm-3 when 45% of the leaf was inundated. The response was logarithmic due to changes in the resistance along the leaf. The internal pressure gradient was predicted for leaves where the leaf surface area was progressively sealed against the influx of gas from the atmosphere. The results suggest that changes in the level and distribution of the lateral input of gas along the leaf would affect both the maximum pressure gradient and the pressure gradient profile within the leaf.