EFFECTS OF SEDIMENT TYPE ON STEM MECHANICAL PROPERTIES OF THE SUBMERGED MACROPHYTE HYDRILLA VERTICILLATA (L.F.) ROYLE

The decline of submerged macrophytes during the eutrophication progress can be partly attributed to the adverse effects of fertile sediment on morphology and physiology of plants. However, little is known about its effects on mechanical properties, although this has been confirmed in terrestrial plants. In this study, the morphological traits, mechanical properties (tensile force, tensile stress and bending index) and cellulose content of Hydrilla verticillata grown on three types of sediment (sand, clay and loam) with different nutrient levels, were examined experimentally. Results showed that considerable variations in mechanical properties of plants were observed among the three sediments and along the stem, with the highest values in clay sediment and a decreased trend from the lower to upper segment, especially when grown in loam sediment, indicating that mesotrophic sediment benefits to higher mechanical resistance of stems than the other two sediments, and plants were prone to break at the other two segments, rather than the lower segment. Stem cross sectional area and internode length were significantly correlated with tensile force, and tensile stress was a linear function of stem cellulose content. Plants grown in clay sediment showed the shortest plant height and the maximum branch numbers, which are morphologically advantageous to reduce the hydraulic force. In conclusion, fertile sediment stimulated the plant growth at the expense of H. verticillata performance with respect to mechanical resistance. Decrease of mechanical resistance could contribute to the decline of submerged macrophytes with the enrichment of sediment nutrient during the process of eutrophication.The decline of submerged macrophytes during the eutrophication progress can be partly attributed to the adverse effects of fertile sediment on morphology and physiology of plants. However, little is known about its effects on mechanical properties, although this has been confirmed in terrestrial plants. In this study, the morphological traits, mechanical properties (tensile force, tensile stress and bending index) and cellulose content of Hydrilla verticillata grown on three types of sediment (sand, clay and loam) with different nutrient levels, were examined experimentally. Results showed that considerable variations in mechanical properties of plants were observed among the three sediments and along the stem, with the highest values in clay sediment and a decreased trend from the lower to upper segment, especially when grown in loam sediment, indicating that mesotrophic sediment benefits to higher mechanical resistance of stems than the other two sediments, and plants were prone to break at the other two segments, rather than the lower segment. Stem cross sectional area and internode length were significantly correlated with tensile force, and tensile stress was a linear function of stem cellulose content. Plants grown in clay sediment showed the shortest plant height and the maximum branch numbers, which are morphologically advantageous to reduce the hydraulic force. In conclusion, fertile sediment stimulated the plant growth at the expense of H. verticillata performance with respect to mechanical resistance. Decrease of mechanical resistance could contribute to the decline of submerged macrophytes with the enrichment of sediment nutrient during the process of eutrophication