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Few studies have focused on the biomechanical responses of submerged, rosette-forming macrophytes to wave action, water depth, or their co-occurrence in naturally eutrophic systems. The plant architecture, root anchorage strength-related traits, leaf morphology, and biomechanics of Vallisneria natans inhabiting a range of water depths were examined along three transects (T1, T2, and T3) in a eutrophic lake, Lake Erhai, in Yunnan Province, China. These transects were exposed to weak wave action and hyper-eutrophication (T1), moderate wave action and eutrophication (T2), or strong wave action and eutrophication (T3). The results showed that V. natans was mainly distributed at intermediate depths, with the widest colonization depth in T1. The values of plant architecture, root anchorage strength-related traits, leaf morphology, and biomechanics were generally highest in T3 and smallest in T2. Along the depth gradient, these values were generally highest at 3.5, 2.5, and 2.5 m for the plants growing in T1, T2, and T3, respectively. These findings suggest that V. natans adopts a “tolerance” strategy to cope with the effects of strong wave action in eutrophic habitats and an “avoidance” strategy when exposed to moderate wave action in eutrophic areas. Since the absence of an avoidance strategy increases the resistance to low-light stress at the expense of increased drag forces, there is a limit to the wave action that V. natans can withstand. This study indicates that biomechanics could be important when determining the distribution pattern of V. natans in Lake Erhai. [ABSTRACT FROM AUTHOR]

Eutrophication and hydrodynamics determine the final distribution patterns of aquatic macrophytes; however, there is limited available knowledge regarding their interactive effects. Morphological and biomechanical responses to eutrophication and hydrodynamic stresses were assessed by sampling five abundant and dominant species, Potamogeton maackianus , P. pectinatus , P. lucens , Ceratophyllum demersum and Myriophyllum spicatum , in three macrophyte beds in Lake Erhai, Yunnan Province, China: one exposed to eutrophication and moderate southeast (SE) wind; one with mesotrophication, but sheltered by the lakeshore, with weak wind disturbance; and one with meso-eutrophication and strong SE wind. The results showed significant interactive effects of eutrophication and hydrodynamics on most biomechanical traits and some morphological traits, suggesting that aquatic macrophytes preferentially undergo biomechanical adjustments to resist the coexisting eutrophication and hydrodynamic stresses. In particular, hydrodynamics increased both the tensile force and tensile strain of P. maackianus under meso-eutrophication and dramatically decreased them in eutrophic areas, suggesting that eutrophication triggers mechanical failure in this species. Additionally, P. pectinatus , C. demersum and M. spicatum showed the lowest and highest values for the biomechanical variables (greater values for M. spicatum ) in the most eutrophic and hydrodynamic areas, respectively, implying that increases in hydrodynamics primarily induce mechanical damage in eutrophic species. The plants generally exhibited greater tensile strain in both shallow and deep waters and the greatest tensile force at moderate depths. The stem cross-sectional area, plant height, stem length, internode length, and branch traits were all responsible for determining the biomechanical variables. This study reveals that hydrodynamic changes primarily induce mechanical damage in eutrophic species, whereas eutrophication triggers mechanical damage in sensitive species. [ABSTRACT FROM AUTHOR]

Submerged macrophytes mainly distribute in the wind-protected littoral zones, rather than continuously distribute around the lake due to mechanical damage by strong wave. However, it is unknown how the biomechanical properties, the key targets against mechanical stress, contribute to its survival and distribution in natural aquatic ecosystem. In this study, the distribution, plant growth, and leaf biomechanical and morphological traits of different segments of Vallisneria natans were examined at 25 sites with three wind strength [sites exposed to strong ES wind (HW), sites exposed to moderate ES wind (MW) and sites sheltered by lakeshore with weak wind disturbance], in Lake Erhai, of Yunnan Province, China. Results showed that V. natans mainly distributed in the wind-protected eastern and northern littoral zones within 5 m water depth. The smallest plant growth, strongest and least flexible leaves were at MW, indicating that V. natans is prone to dominate the littoral zones exposed to strong but short wave. Additionally, the high plant growth and relatively stronger and less flexible leaves at HW suggested that the maximization of photosynthesis was at the cost of reduced biomechanical properties and increased drag forces from similar waves, which were unfavourable to complete their life cycles and ultimately reduce the survival and distribution of V. natans under strong wave disturbance. The significant associations between the biomechanical and morphological traits may trigger trade-offs between the mechanical resistance and other plant functions, such as photosynthesis, ultimately determining survival and distribution of submerged macrophytes in natural aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Variability in biomass allocation and growth rate of submersed macrophytes along water depth gradients may lead to different carbon (C), nitrogen (N) and phosphorus (P) stoichiometric characteristics. We conducted a field investigation to evaluate long-term effects of water depth on C, N and P stoichiometry of three submersed macrophytes, Potamogeton maackianus, Myriophyllum spicatum and Ceratophyllum demersum. The results indicated that shoot C:N, C:P and N:P of the plants tended to increase with elevated water depths, and patterns of biomass allocation along water depth gradients were more important than biological dilution of increased growth rates in affecting shoot C:N:P stoichiometric characteristics of the plants. Partial correlation analysis using shoot height and biomass as covariates revealed that water depth significantly affected C:P ratios in shoots of P. maackianus and M. spicatum and C:N ratio in shoots of M. spicatum, but did not affect N:P ratios of all the plants. Shoot stoichiometry of M. spicatum was most sensitive in response to water depth, followed by P. maackianus, and that of C. demersum was really unchanged with elevated water depths. Our results suggested that strategies in biomass allocation in organs, which depend largely on the species identity, rather than growth rates of the plants, contributed mainly to variation in the observed element stoichiometry along the water depth gradients. [ABSTRACT FROM AUTHOR]

Decline of submersed macrophytes has occurred in eutrophic lakes worldwide. Little is known about effects of nutrient enrichment on biomechanical properties of submersed macrophytes. In a 30-day experiment, Myriophyllum spicatum was cultured in aquaria containing two types of sediment (mesotrophic clay vs. fertile loam) with contrasting water NH concentrations (0 vs. 3.0 mg L NH-N). The plant growth, shoot and root morphology, stem biomechanical properties, and stem total nonstructure carbohydrates content (TNC) were examined. The NH-enriched water, particularly combined with the fertile sediment, caused adverse effects on M. spicatum as indicated by reductions in the growth, stem biomechanical properties (tensile force, bending force and structural stiffness), and TNC content. These results indicate that increased sediment fertility and water NH-enrichment made the plant more fragile and vulnerable to hydraulic damage, particularly for the upper stem, implying that M. spicatum was prone to uprooting and fracture by hydraulic force, and the broken fragment from parent shoot of M. spicatum might have low-survival potential due to its low-TNC content. This may be a mechanical aspect for the decline of submersed macrophytes and makes it more difficult to restore submersed vegetation in the eutrophic lakes. [ABSTRACT FROM AUTHOR]

The relationships between relative growth rate and its components across 11 submersed macrophytes were examined in a short-term experimental study. Plants were grown in identical conditions in pots that were submersed in tanks. The average values for relative growth rate ranged from 17.4 to 94.5mg g-1d-1. The net assimilation rate, based on the increase in plant dry weight per unit leaf area in a fixed time, varied fivefold among species and showed a strong, positive correlation with relative growth rate. The leaf area ratio, leaf mass ratio, and specific leaf area were not significantly correlated with the relative growth rate, although these parameters were important in the adaptive responses of macrophytes to environmental stress. These results suggest that the physiological components (net assimilation rate) would be the main determinant of relative growth rate in submersed macrophytes, which highlights the importance of net assimilation rate in explaining differences in macrophyte species performance in freshwater habitat. [ABSTRACT FROM AUTHOR]

Little is known about the mechanical resistance response of submerged macrophytes to floods. An experiment was conducted to investigate the plant growth, root anchorage strength, and stem tensile properties of five submerged macrophytes under three initial water levels (1.0, 2.5, and 4.0 m) with four water level fluctuation speeds (0, 5, 15, and 25 cm d). Our results demonstrate that the biomass, relative growth rate, root anchorage strength, and stem tensile properties of the five species decreased with increasing initial water level, suggesting that deep water can inhibit plant growth and decrease their mechanical resistance. Floods weakened the stem tensile properties and strengthened the root performances of Myriophyllum spicatum, Hydrilla verticillata, and Potamogeton malaianus in shallow water. However, floods induced opposite mechanical resistance responses from plants in deep water, indicating a possible trade-off between stem breakage and uprooting under flooding conditions. M. spicatum, Ceratophyllum demersum, and P. malaianus were more tolerant of deep water and flood intensity than Potamogeton maackianus and H. verticillata, as indicated by their larger biomass, plant heights, stem tensile properties, and root anchorage strength. This is the first article that mechanically explains the competitive capability and survival potential of submerged macrophytes to water depth and flood intensity. [ABSTRACT FROM AUTHOR]

Highlights: [•] We evaluate the effects of water depths on C, N and P stoichiometry of five submersed macrophytes. [•] Water depths affected growth of the plants significantly but weakly affected the plant C, N and P stoichiometry. [•] The plant species and their organs explained most of the variance in the C, N and P stoichiometry. [Copyright &y& Elsevier]

Abstract: The uptake kinetics of phosphate (Pi) by Myriophyllum spicatum was determined from adsorption and absorption under light and dark conditions. Pi uptake was light dependent and showed saturation following the Michaelis–Menten relation (in light: V =16.91×[Pi](1.335+[Pi]), R 2 =0.90, p <0.001; in the dark: V =5.13×[Pi](0.351+[Pi]), R 2 =0.77, p <0.001). Around 77% of the loss of Pi in the water column was absorbed into the tissue of M. spicatum, and only 23% was adsorbed on the surface of the plant shoots. Our study shows that M. spicatum shoots have a much higher affinity (in light: 3.9μmolg−1 dwh−1 μM−1; in the dark: 3.7μmolg−1 dwh−1 μM−1) and V max (maximum uptake rate, shoot light) for Pi uptake than many other aquatic macrophytes (in light: 0.002–0.23μmolg−1 dwh−1 μM−1; in the dark: 0.002–0.19μmolg−1 dwh−1 μM−1), which may provide a competitive advantage over other macrophytes across a wide range of Pi concentrations. [Copyright &y& Elsevier]