Kaining Chen

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 180 cm) 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.

Impacts of four emergent macrophytes on sediment nutrient loading

Acorus calamus, Zizania latifolia, Phragmites communis and Typha latifolia are four common emergent macrophytes in some wetlands. To evaluate the influence of the four emergent macrophytes on sediment nutrient loading, a field experiment was conducted. Sediment physicochemical characters, nutrient distribution properties and -N and -P fluxes were investigated. Compared with the control without macrophytes, sediment moisture content, porosity, loss on ignition and total P were higher, while wet bulk density, total N, -N and -N were lower. Concentrations of -N and -P in interstitial water were higher than in overlying water, indicating that they were diffusing from sediment to overlying water. -N and -P concentrations near the sediment surface displayed exponential increases with sediment depth and reached a maximum at 5–8 cm. Fluxes of -N and -P were also lower in sediment with macrophytes. Among the four macrophytes, sediment moisture content and porosity increased, while wet bulk density decreased with A. calamus and Z. latifolia. N and P contents were lower with T. latifolia, while -N and -N were lower with A. calamus and Z. latifolia. A. calamus and T. latifolia had lower -N concentration in interstitial water, and A. calamus had lower -P. Compared with other treatments, T. latifolia restricted -N and -P release effectively due to their lower fluxes (0.082 and 0.010 mg m−2 d−1). This study also elucidates the differences among the four macrophytes in affecting sediment nutrient loading, which is meaningful for macrophyte selection in wetland restoration.

Seed bank characteristics of the Nymphoides peltata population in Lake Taihu

The Nymphoides peltata (N. peltata) population has shown rapid expansion in Lake Taihu, China, in recent years. The core question is whether N. peltata seeds have contributed to the expansion. To address this, we randomly selected three N. peltata stands to investigate the seed bank characteristics of N. peltata in Lake Taihu. Results showed that N. peltata had high seed production, with a maximum seed yield of 1763 seeds per m2. Density of intact and fragmented seeds decreased rapidly with sediment depth. Few intact or fragmented seeds were distributed at depths greater than 4 cm in the sediment. Spatial distribution of the seed bank indicated that most seeds sank to the sediment within the N. peltata stands, and few seeds took advantage of their floating ability. Seeds recovered from the sediment during April to June had a low germination rate, and no seeds germinated during October to April. Cold exposure treatment increased the germination rate remarkably. No seedlings were found in the field from January 2012 to December 2012, indicating that few seeds were successfully established in the surveyed area. The results suggested that sexual reproduction had little direct contribution to the N. peltata expansion in this large shallow lake.