Comparative responses of two water hyacinth (Eichhornia crassipes) cultivars to different planting densities

• The common water hyacinth (CWH) and purple root water hyacinth (PRWH) were used to investigate the effect of planting densities on the root traits, physiological and microbial diversity.
• The result of ROL suggests that larger Δ root length and root porosity could help improve the dissolved oxygen of water column.
• The capacity of PRWH release oxygen into the water column was better than those of CWH.
• The microbial diversity was significantly affected by planting density.

Two water hyacinth cultivars, i.e., common water hyacinth (CWH) and purple root water hyacinth (PRWH), were used to investigate the effect of planting densities (i.e., 8, 16 and 24 plants per bucket with a volume of 1.1 m × 1 m (diameter × depth)) on root traits, physiological characteristics, and microbial diversity. The results indicated that the planting density significantly influenced root traits, photosynthesis, radial oxygen loss (ROL), dissolved oxygen (DO), and microbial diversity of water hyacinths. The root porosity, root diameter, and root chlorophyll of PRWH were higher than those of CWH, and CWH had higher chlorophyll and Pn in leaves. The microbial diversity decreased significantly with increasing plant density for CWH, while it increased and then decreased in PRWH and peaked at 16 plants bucket−1. The results suggested that the aerenchyma of PRWH was more developed than those of CWH, and CWH had higher leaf photosynthesis. However, higher root chlorophyll a in PRWH indicated that its capacity for photon capture was higher than in CWH. The result of ROL suggests that larger Δ root length and root porosity could help improve the dissolved oxygen of water column. The photosynthesis of CWH and PRWH can release oxygen into water column, and the capacity of PRWH was better than those of CWH.