The influence of water level fluctuations on the growth of four emergent macrophyte species

The influence of the amplitude of cyclic water level fluctuations on the growth of four species of emergent macrophyte (Cyperus vaginatus, Phragmites australis, Triglochin procerum and Typha domingensis) was studied in a controlled, pond-based experiment. The amplitudes of water level fluctuations were static, ±15, ±30 and ±45 cm, each cycling over a forty-day period. In all treatments the water level fluctuated around an initial water depth of 60 cm. Within each amplitude treatment, plants were grown at three elevations with the sediment surface at 20, 40 or 60 cm. Only T. domingensis and P. australis showed a significant response to amplitude. Biomass of T. domingensis was similar in the static, ±15 and ±30 cm amplitude treatments but dropped by ca. 52% when grown in amplitudes of ±45 cm. In contrast, the largest biomass for P. australis occurred in the ±30 cm amplitude treatment suggesting this species prefers moderately fluctuating water levels. The response of P. australis to amplitude was contingent upon elevation with plants growing in the ±45 cm amplitude, low elevation treatment having particularly low biomasses. C. vaginatus biomass increased with increasing elevation but did not respond to amplitude while T. procerum did not respond to either amplitude or elevation likely due to the ability of the species to photosynthesise under water. The relative growth rate and the average emergent surface area were logarithmically related in C. vaginatus suggesting flooding of the photosynthetic canopy was limiting the ability of this species to acquire atmospheric carbon. No clear relationship was found for T. domingensis or P. australis indicating that a factor other than access to atmospheric carbon was restricting the growth of these species.