Growth responses of eight wetland species to water level fluctuation with different ranges and frequencies

Abstract

Fluctuation range and frequency are two important components of water level fluctuation, but their effects on wetland plants have not been evaluated separately. We subjected eight wetland species to a control treatment with static water level and fluctuation treatments with different ranges or frequencies to examine their effects on plant growth. Acorus calamus, Butomus umbellatus and Iris wilsonii showed high survival rates in all treatments with various fluctuation ranges and frequencies. Their survival rates were higher at the medium fluctuation frequency than at the low and high frequencies, suggesting beneficial effects of the medium frequency. In the experiment comparing the fluctuation ranges, A. calamus and I. wilsonii could maintain the capacity for asexual propagation and accumulate higher biomass compared with the control plants, while biomass of the other six species dramatically decreased. In the experiment comparing fluctuation frequency, species with relatively high survival rates (≥ 50%) maintained or increased the capacity of asexual propagation, and A. calamus and I. wilsonii allocated relatively more biomass to roots, which may enhance plant growth and survival. In contrast, these species did not show increased biomass allocation to shoots in response to both fluctuation range and frequency, presumably because shoots are prone to mechanical damage caused by streaming floodwater. Taken together, biomass accumulation in roots rather than in shoots and the ability to asexually propagate are important for the survival of these species during water fluctuation.

Fig 1. Settings of different water fluctuation ranges and frequencies.

The treatments were: C–water depth was maintained constantly at 75 cm; SR–water depth changing between 50 and 100 cm twice (two cycles); MR–water depth changing between 25 and 125 cm twice; LR–water depth changing between 0 and 150 cm twice; LF–water depth changing between 0 and 150 cm twice; MF–water depth changing between 0 and 150 cm four times; HF–water depth changing between 0 and 150 cm eight times, during the 80-d experiment.

Fig 2. Total biomass, shoot biomass and root biomass of eight common riparian plants after 80-d treatments with different ranges of water level fluctuation.

For each species, means of treatments with different letters are significantly different at P = 0.05. Data are mean values ± s.e.

Fig 3. Total biomass, shoot biomass and root biomass of eight common riparian plants after 80-d treatments with different frequencies of water level fluctuation.

For each species, means of treatments with different letters are significantly different at P = 0.05. Data are mean values ± s.e.

Fig 4. Plant height, ramet number and root-to-shoot (R/S) ratio of eight common riparian plants after 80-d treatments with different ranges of water level fluctuation.

For each species, means of treatments with different letters are significantly different at P = 0.05. Data are mean values ± s.e.

Fig 5. Plant height, ramet number and root-to-shoot (R/S) ratio of eight common riparian plants after 80-d treatments with different frequencies of water level fluctuation.

For each species, means of treatments with different letters are significantly different at P = 0.05. Data are mean values ± s.e.