Growth and diet of European catfish (Silurus glanis) in early and late invasion stages

Ottelia alismoides is now at risk of extinction and listed as a threatened aquatic plant species in China. We investigated the responses of O. alismoides to four amplitudes (static, +/- 25, +/- 50 and +/- 75 cm) of water level fluctuations. In all treatments, the water level fluctuated around in initial water depth of 100 cm. Within each amplitude treatment, two fluctuating frequencies were chosen: two cycles (low frequency) and six cycles (high frequency) during the 72 days of the experiment. Leaf characters (number and area) were not affected by the amplitudes. Below-ground dry weight (DW) allocation was proportionally similar in all treatments. Though there were no significant differences between the static and fluctuating water levels in the total DW, total DW had a decreasing trend in the +/- 75 cm amplitude. Interestingly, the largest total DW for O. alismoides Occurred in the +/- 25 cm amplitude suggesting the species prefers moderately fluctuating water levels. Fruit DW allocation and fruit number were similar in all water regimes, but seed number per fruit decreased in the +/- 75 cm amplitude. O. alismoides generally did not respond to the fluctuating frequencies. We conclude that O. alismoides can tolerate moderate water level fluctuations, but high fluctuating amplitude (+/- 75 cm) reduced the plant performance. Decisions related to conservation of this species should take the disturbance caused by water level fluctuations into consideration.