Sedimentation in itself is simply the process of depositing sediment in both coastal and freshwater ecosystems. Sediment is any particulate matter that can be transported by fluid flow, such as clays, silts, or sands. Healthy freshwater ecosystems necessitate sediment inputs. However, excessive amounts of sediment can result in the destruction of aquatic habitat and a reduction in the diversity and abundance of aquatic plants. Therefore, human undertakings are adding to higher amounts of sedimentation at a rate which is deemed to be disadvantageous to wetland species.
Deep burial is usually inhibitory to plant growth for almost all species due to lower oxygen availability in root zones. Wetland plants undergo burial by sediment also evolve a variety of adaptations. Generally, plants allocate more biomass and nutrient to above-ground parts to grow out of the sediment. Furthermore, plants develop short and thick roots to increase oxygen transportation availability. However, a thick and short root is unfavorable for nutrient acquisition due to a low root-soil contact. Therefore, there exists a contradiction for plant roots to acclimate to deeper burial or infertile sands simultaneously.
Moreover, sedimentation effect may vary with sediment type due to different nutrient contents. Infertile sediment might aggravate the damage of deep burial on plant growth, while the damage might be alleviated in the fertile sediment since more nutrients can be supplied for plant growth. As a result, fertile sediment might be favourable for counteracting the negative effects of deep burial than did infertile one, which needs for further confirmation.
Dongting Lake, the second largest freshwater lake in China, receives a large amount of silt from “Three Channels” (Songzi, Taiping and Ouchi) connected with Yangtze River, and from “Four Rivers” (Xiang River, Zi River, Yuan River and Li River) of Hunan Province annually. Sedimentation is a major driving force regulating succession model of vegetation in the Dongting Lake wetlands. Dr. PAN Ying carried out a study to explain the morphological and physiological responses of Miscanthus sacchariflorus to acclimate to sedimentation, by growing ramets in two sediment type (clay and sand) combined with three burial depth (0, 6 cm and 12 cm), a total of five treatment (no burial, 6 cm sand, 6 cm soil, 12 sand and 12 cm soil).Researchers found that first, fertile clay played a role in compensating for the growth loss induced by deep burial. Second, biomass and plant nutrient had been transported from below-ground tissues to above-ground tissues along with increasing burial depth to grow out of the sediment surface. Third, roots became shorter and thicker along with increasing burial depth to facilitate the aeration of root systems under deep burial conditions. The most important is that compared to the clay burial, more biomass and plant nutrient had been allocated to below-ground tissues in the sand burial treatments to increase nutrient acquisition.
These data indicate that wetland plants will not be influenced by shallow burial through adjustments of biomass allocation and root morphology, and that clay facilitates wetland plants to acclimation to deep burial due to sufficient nutrient supply.
This research has enriched our knowledge of the harmful mechanisms of sedimentation on the growth of wetland plants. This research was supported by the Knowledge Innovation Program of the Chinese Academy of Science(KZCX2-YW-435), the National Basic Research Program of China (2012CB417005) and the National Natural Science Foundation of China (31070325). The main findings of this study have published on Fundamental and Applied limnology (DOI: 10.1127/1863-9135/ 2012/0266).