INTERNAL NUTRIENT LOAD ON THE GROWTH, MORPHOLOGY, AND RESOURCE ALLOCATION STRATEGIES OF FOUR COMMON SUBMERGED PLANTS

Internal nutrient is one of the important causes of eutrophication in lakes, exerting notable impact on the physiology and growth of submerged plants. In order to explore the effects of internal nutrient loading on the growth, morphology, and resource allocation of submerged plants, this study managed sediment nutrient concentrations and scrutinized the responses of diverse functional traits within four prevalent submerged plant species: Vallisneria natans, Hydrilla verticillata, Myriophyllum spicatum and Potamogeton wrightii. The results showed that: (1) The increase of internal nutrient loading promoted a stimulating effect on the growth of the four submerged plants, with Vallisneria natans displaying higher population quantity and total biomass compared to the other submerged plants. However, a decline in population numbers across all four species was observed when sediment nutrient content became excessive (C: 73.33 mg/g; N: 4.94 mg/g; P: 0.68 mg/g). (2) The response trend of submerged plant morphological characteristics to changes in sediment nutrient content exhibited variability. The height of all species gradually increased, while there was no significant change in root length. Individual fresh weight of V. natans and P. wrightii continued to increase, while the fresh weight of H. verticillata and M. spicatum first increased and then decreased. (3) Alterations in internal nutrient content significantly influenced the resource allocation of the four plants. As sediment nutrient content increased, the proportion of aboveground biomass within the submerged plants significantly increased, leading to a concurrent decline in the root-to-shoot ratio. Furthermore, the content of photosynthetic pigments exhibited a marked increase with enhanced sediment nutrient content. However, it is important to note that excessive nutrient content negatively impacted the synthesis of photosynthetic pigments. In summary, the results of this study indicate that the adaptability of V. natans to changes in sediment nutrient loading is the strongest, so selecting V. natans as a pioneer species for ecological restoration in eutrophic water bodies can effectively improve the restoration efficiency of submerged macrophytes.