Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences

Sensitivity of freshwater macrophytes to UV radiation: relationship to depth zonation in an oligotrophic New Zealand lake

Rowena Rae, Rowena Rae, Dieter Hanelt, Dieter Hanelt, Ian Hawes and Ian Hawes

Marine and Freshwater Research 52(7) 1023 - 1032
Published: 15 November 2001


The ultraviolet radiation (UVR) responses of photosynthesis by two freshwater vascular plants, Potamogeton cheesemanii and Isoetes alpinus, and the characean algae Chara fibrosa and C. corallina in Lake Coleridge, New Zealand, were investigated. Experiments comprised 4–5 h of exposure to different UV wavelengths followed by 17 h of recovery in low light. Photosynthetic competence was assessed by pulse-amplitude-modulated fluorometry. The four species showed different sensitivities to UVR, which were consistent with their upper depth limits. The shallowest-growing species, P. cheesemanii, was uninhibited by UVR, whereas after 5 h of exposure to UVR, inhibition of 15%, 38% and 48% was measured for I. alpinus, C. fibrosaand C. corallinacollected from 4 m, 6.2 m and 16.5 m, respectively. Not all plants recovered fully from UVR inhibition. Plants from upper and lower depths of their growth range did not generally differ in inhibition sustained or ability to recover photosynthesis. The species with greatest tolerance of UVR also contained the highest concentrations of UVR-absorbing pigments. Freshwater macrophytes have differing abilities to tolerate UVR exposure through repair and/or protection strategies and these may be related to their vertical zonation.

Keywords: variable fluorescence, photoinhibition, UVR-absorbing compounds

© CSIRO 2001

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