Variations in leaf pigment content and photosynthetic activity of Phragmites australis in healthy and die-back reed stands of Lake Fertõ/Neusiedlersee

Abstract

The photosynthetic capacity of the common reed (Phragmites australis /Cav./ Trin. ex Steudel) was studied in various reed stands in the littoral zone of Lake Fertõ. Measurements were performed in three healthy and two dieback reed stands in the summer of 1997. In the leaves of declining reeds, the chlorophyll content was lower than in the vigorous sites. In the former sites, there was a significant rise in the total carotenoid pool (320–480 mmol mol⁻¹chl (a + b)) as compared to that of the vigorous sites (250–350 mmol mol⁻¹ chi (a + b). The size of the xanthophyll cycle pool and the β-carotene content of leaves significantly increased in the die-back sites. In early summer, the potential photochemical quantum efficiency of Photosystem II (Fv/Fm) did not differ considerably (0.79–0.81) from site to site, yet by August it significantly decreased (0.74–0.77) in the die-back sites as compared to the vigorous sites. The maximum CO₂ assimilation rate measured on the 3rd and 4th leaves ranged from 11 to 17 CO₂ μmol m⁻² s⁻¹ and from 9 to 12 CO₂ μmol m⁻² s⁻¹ in the vigorous sites and the die-back sites, respectively. The stomatal conductance was also lower in the die-back sites (200–350 mmol H₂O m⁻² s⁻¹) than in the vigorous reed stands (380–510 mmol H₂O m⁻²s⁻¹) which might result in the functional impairment of the gas ventilation system of the declining reeds, and consequently in oxygen deficiency and damage to the rhizome.