Impact of water depth and sediment type on root morphology of the submerged plant Vallisneria natans

The environment of Lake Taihu has changed a great deal in recent decades. Wetland plant restoration is considered an efficient way to keep it healthy. However, restoration efforts are affected by environmental factors which have important influences on wetland plant growth. In order to study the mutual effects of water depth and sediment type on the growth of aquatic plants, the impacts of the two environmental factors on root morphology of the submerged plant Vallisneria natans were investigated in an outdoor pond experiment. Treatments included three levels of water depth (60, 120 and 180cm) and two sediment types (clay and sandy loam). Results showed that root/leaf mass ratio and root morphological parameters (root diameter, root length, root area, root volume, specific root length and specific root area) of the plant generally decreased with increasing water depth, with reductions of 12.64% in root diameter and 97.40% in root mass in clay and 28.82% in root diameter and 97.98% in root volume in sandy loam. Root/leaf mass ratio in low nutrient sediment (sandy loam) was higher than that in the more nutrient-rich sediment (clay). However, the other four morphological parameters were higher in clay at any water depths. Results of two-way analysis of variance (ANOVA) showed that water depth impacted the biomass allocation and root morphology of V. natans significantly, while sediment type only had significant impact on root/leaf mass ratio and root diameter. The results indicate that a considerable variation in root morphology of the submerged plant V. natans exists in response to water depth and sediment type, and water depth is the key ecological factor affecting root growth of the plant. This study can provide useful information in aquatic plant restoration and management.