In wetlands, water levels can fluctuate, which often disturbs local organisms, such as aquatic plants. The responses of Alternanthera philoxeroides, Myriophyllum aquaticum, and Ludwigia adscendens to water level fluctuations of different frequencies were examined here. Methods
Water level fluctuations were simulated at four frequencies: static (0 frequency), one cycle (1 frequency), two cycles (2 frequency), and four cycles (4 frequency), and with fluctuation amplitudes (± 25 cm) during a 60 day experiment. Morphological and physiological traits of plants, including branching number, shoot length, total biomass, shoot root ratio, chlorophyll content, and maximum PSII quantum efficiency(Fv/Fm) were assessed. Important findings
Water level fluctuation was found to have no significant impact on branching number, root shoot ratio, or Fv/Fm of A. philoxeroides,but all scenarios except 1 frequency were significantly associated with longer shoots and lower total biomass and chlorophyll content. The traits of M. aquaticumshowed different responses to water level fluctuation: branching number and Fv/Fm showed no changes, but shoot length (2 frequency) and root shoot ratio (1 and 4 frequency) increased significantly, and total biomass and chlorophyll content (expect 4 frequency) decreased. In L. adscendens, water level fluctuation was associated with lower branching number in all scenarios except 2 frequency, shoot length in all scenarios except 1 and 2 frequency, total biomass in all scenarios except 2 frequency, and chlorophyll content but had no significant effects on root shoot ratio or Fv/Fm. Under most water level fluctuation conditions, the branching number, shoot length, total biomass, chlorophyll content, and Fv/Fm of L. adscendens were significant higher than those of A. philoxeroides and M. aquaticum, and the latter two had no significant differences.Results
suggested that water level fluctuations were the limiting factor for the growth of three species in autumn. Alternanthera philoxeroides and M. aquaticumdid not show higher invasiveness in environments in which the water level fluctuated in autumn but did show higher tolerance and plasticity in response to water level fluctuations in general. This was related to the invasiveness of introduced species.Results
also indicated that preventive efforts focusing on potential invasion by M. aquaticum should be strengthened.