Tidal Effects On The Biomechanics-morphology-structure Characteristics Of Wetland Plants

The salt marsh plant communities in coastal wetlands can serve as a coastal barrier.However,the tides have also had a great impact on plant communities due to sea-level rise.Phragmites australis and Spartina alterniflora are two typical plants affected by tides in the Yellow River Delta.In this study,the differences in the morphological characteristics,biomechanical characteristics,and structural components of plants in the Yellow River Delta between tidal zone and sheltered zone were investigated;the indoor wave-making experiment was used to explore different wave frequency conditions;the biomechanical response of plants in roots,stems,leaves was also investigated after long-term wave action;finally,we used the finite element theory combing with the ANSYS model to carry out plant simulation modelling which simulated the tidal pressure on wetland plants.The results were as follows:1)The tide had no significant effect on the morphological characteristics of S.alterniflora,however,it had a very significant effect on the P.australis,which tidal zone plants showed thicker stem diameter,lower plant height but higher biomass than sheltered zone plants.The tensile strength and bending resistance of S.alterniflora were higher than that of P.australis,but P.australis showed higher equivalent stress,which meant the force per unit area was stronger.What's more,the lignin and cellulose of P.australis showed higher than that of S.alterniflora.2)The two species showed obvious differences in morphological characteristics after treatment in two-wave frequencies.The stem diameter of the wave group was significantly higher than that of the control group,corresponding to the obvious difference in the bending resistance of the plant stem.The wave frequency with 20 n/min had higher stem bending resistance than the plants with wave frequency of 40 n/min.The roots of P.australis in the wave group had stronger tensile strength,but S.alterniflora did not show this phenomenon.3)The plant model simulated by ANSYS simulation had similar mechanical characteristics with the real situation so that they could be used to do simulation.Among the conditions of static tension and pressure,the deformation of S.alterniflora was greater than that of P.australis if they had the same diameter,which confirmed that P.australis plant material has stronger strength properties.Applying this model to the stress analysis in natural,it found that although the plant stem diameter of S.alterniflora was nearly doubled of P.australis,the deformation caused by the equivalent stress had significantly reduced(about twentieth of that).It showed that although the material strength properties of P.australis were higher than that of S.alterniflora,the thickness of the stem could mostly reduce the external forces.The native species P.australis mainly resisted external forces by enhancing its material intensity,while the invasive species S.alterniflora developed the thick stem diameter to resist external forces.The results can help managers to manage and restore wetland in more details.