Short-time response in root morphology of Vallisneria natans to sediment type and water-column nutrient

Rooted submerged macrophytes can absorb significant amounts of nutrients from both sediment and water. We investigated root morphology of Vallisneria natans in mesocosm plastic bins, in response to three types of sediment (sandy loam, clay, and a 50:50 (v/v) mixture of the two sediments) and two levels of water-column nutrient (well water and nutrient medium). Compared to the plants grown in the clay or mixed sediments, root diameter decreased (0.39-0.41 versus 0.36-0.37 mm) but total root length per plant increased (0.87-1.27 versus 1.14-1.62 m) when grown in sandy loam. Increase of nutrient availability in water column led to decreased specific root length (306-339 versus 258-281 m g−1). However, both sediment type and water-column nutrient had no impacts on root number (ranged from 19 to 24 number of roots per plant). Root weight ratio, root:leaf mass ratio and root:leaf length ratio generally decreased with enhanced nutrient availability in sediment or water. Plant growth was affected by sediment type alone (P < 0.05), rather than water-column nutrient (P > 0.05). However, plant N and P contents were significantly impacted by both sediment type (P ≤ 0.001) and water-column nutrient (P < 0.05). Increase of nutrient availability in sediment or water led to increased plant N (ranged from 2.47 to 4.77 mg g−1) and P concentrations (ranged from 42.8 to 62.0 mg g−1). These results indicate that considerable variation in root morphology of V. natans exists in response to the fertility of the sediment it is rooted in.