Physiological and anatomical characterisation of Phragmites australis leaves

The anatomy, biochemistry and physiology of Phragmites leaves have been investigated. Biochemical and physiological measurements indicate that Phragmites australis leaves have a C3 mechanism of carbon fixation. However, structural and ultra-structural observations of young leaves are more reminiscent of a C4-like anatomy. In addition, chloroplasts apparently fully competent for photochemical and biochemical reactions were in both the mesophyll and in the bundle sheath cells of young leaves. The activity of the principal enzyme involved in carbon metabolism, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), was high under ambient conditions (59.8 and 64.2molm-2 s-1, respectively in mature and young leaves). In contrast, phosphoenolpyruvate carboxylase activity was low in both mature and young leaves (7.8 and 8.1molm-2 s-1, respectively) Despite the high Rubisco activity, the rate of photosynthesis of Phragmites leaves on a leaf area basis was low. We investigated if resistances to CO2 entry in the leaves could limit photosynthesis. However, stomatal and mesophyll resistances to CO2 diffusion in Phragmites leaves were comparable to those of terrestrial plants and did not restrict intercellular CO2 concentration significantly.