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 Fert6. Measurements were performed in three healthy and two die­ back 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 ,B-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 C02 assimilation rate measured on the 3rd and 4th leaves ranged from 11 to 17 C02f..i.mol m-2 s-1 and from 9 to 12 C02f..i.mol 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 H20 m-2 s-1) than in the vigorous reed stands (380-510 mmol H20 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.