Effects of sediment anoxia on growth and root respiratory metabolism of Iris pseudacorus: Implications for vegetation restoration of eutrophic waters in China

In many ecological restoration projects conducted in eutrophic waters of China, vegetation recovery is usually restricted by highly organic sediment characterized with anoxic conditions. The effects of sediment anoxia on growth and root respiratory metabolism of Iris pseudacorus were investigated using modified rhizobox systems with sediment anoxia simulated through sucrose/agar addition into sediment. The anoxia levels simulated included control (without sucrose addition), moderate anoxia (MA, 0.5% sucrose addition) and high anoxia (HA, 1.0% sucrose addition). The results indicated that the total biomass, relative growth rate (RGR), number and mean length of leaves and tiller number did not differ between the three anoxia levels (p > 0.05). However, the redox condition of sediment significantly affected the biomass allocation, root:shoot ratio (R:S ratio) was 18.9% and 50.3% higher in the MA and HA treatments, and the roots were denser and shorter in anoxic conditions than in controls. There were no significant differences in physicochemical properties (redox potential and pH) between rhizospheric and non-vegetated sediment (p > 0.05). The present study indicated that I. pseudacorus has a strong resistance to sediment anoxia through increasing root production and anaerobic respiration, which enables it to be an appropriate pioneer species in vegetation restoration engineering.