The behavior in flow of the morphologically variable seaweed Hedophyllum sessile (C. Ag.) Setchell

Drag force was measured on individual specimens of Hedophyllum sessile in a variable-speed flow tank. Those from sheltered localities, which are broad, bullate blades, experience greater drag at a given water velocity than ones from localities more exposed to the action of waves, which have smooth, deeply dissected blades. All specimens rearranged their blades as water velocity increased, resulting in a decrease in effective drag at higher water speeds, but individuals with smooth, dissected blades assumed a more compact shape at high current speeds and thus reduced their effective drag over that of broad-bladed individuals at the same speed. In habitats chronically exposed to strong wave action, drag reduction may be an important survival mechanism; in calm habitats the turbulence induced by lack of such streamlining may enhance mixing of the water in the immediate vicinity of a plant.     

Drag and reconfiguration of freshwater macrophytes

SUMMARY 1. Submerged freshwater macrophytes face large hydrodynamic forces in flowing waters in streams and on wave‐swept lake shores and require morphological adaptations to reduce the drag and the physical damage. This experiment studied five species of freshwater macrophytes and strap‐formed plastic leaves to test the predictions that: (i) increasing flexibility leads to greater reconfiguration and lower drag coefficients, (ii) flexible plants experience a steeper decline of drag coefficients with increasing water velocity than unflexible plants and (iii) plants mounted vertically on a horizontal substratum bend over in fast flow attaining a shielded position of low drag. 2. The results confirmed all three predictions. In fast flow, plants mounted upright on a horizontal platform gradually approached a position aligned with the flow, depending on their flexibility. In the range 8–50 cm s^?1 the deflection followed an interspecific negative linear relationship between log (tangent Φ) and velocity, where Φ represents the shoot angle normal to the horizontal level. Above 50 cm s^?1, further deflection was reduced perhaps by a combination of the elasticity and packing of shoots and the increasing lift generated by fast flow. 3. Drag coefficients of plants ranged between 0.01 and 0.1, typical of moderately to very streamlined objects. Drag coefficients declined log‐log linearly at increasing velocity, following negative slopes between ?0.67 and ?1.24 (median: ?1.0) because of reconfiguration and formation of a shielding canopy. Drag coefficients declined much less (median: ?0.55) for plants floating freely in the streaming water and which were capable of changing their shape but unable to form a shielding canopy. Drag coefficients declined even less for relatively unflexible plastic leaves (?0.30 to ?0.40), and they remained constant for stiff, bluff objects. 4. The experiments suggest that flow resistance of flexible, submerged macrophytes in natural streams may increase in direct proportion to water velocity because they form a shielding submerged canopy, and high water stages at peak flow may result in greater proportions of the water passing unimpeded above the canopy. In contrast, stiff amphibious and emergent reed plants should experience an increase of flow resistance with at least the square of velocity as reconfiguration is small and former aerial plant surfaces come into contact with the streaming water at higher water stages. Field experiments to test these predictions are urgently needed.     

Morphological correlates of river velocity and reproductive development in an ornamented stream fish

Adaptive phenotypic divergence can arise when environments vary in ways favoring alternative phenotypic optima. In aquatic habitats, the costs of locomotion are expected to increase with water velocity, generally favoring a more streamlined body and the reduction of traits that produce drag. However, because streamlining in fish may come at the cost of maneuverability, the net benefits of drag reduction can differ not only among habitats, but also among individuals (or classes of individuals) that rely on locomotion for different uses (e.g., males vs. females or adults vs. juveniles). We tested these predictions by exploring relationships among river velocity, body streamlining, ornamental fin size, and male reproductive condition in the steelcolor shiner (Cyprinella whipplei), a small-bodied North American cyprinid. Overall, males in peak reproductive condition (defined by the development of sexually dimorphic tubercles) had less streamlined bodies and larger ornamental fins than males in lower reproductive condition or individuals lacking these secondary sexual characters (females and immature males). There was a relationship between river velocity and body streamlining only for males in peak reproductive condition, but it was in the opposite direction of our predictions: these males were less streamlined in faster rivers. We found only weak support for the prediction that ornamental fin size would be negatively associated with river velocity. Overall, these results suggest either that drag is not an important selective pressure in these habitats, or that the sexual selection advantages of a deep body and large fin compensate any natural selection costs for C. whipplei males. This study highlights the often overlooked diversity of selective pressures acting on streamlining in fishes, and can offer novel insights and predictions allowing a more nuanced understanding of fish ecomorphology.     

Field measurements of wind speed and reconfiguration in Arundo donax (Poaceae) with estimates of drag forces

The giant reed (Arundo donax) is well known as a species that can withstand high wind loads without mechanical damage. To examine wind impact, profiles of vertical wind speeds in the plant's natural habitat (southern France) were measured at the edge and within a stand in the main wind direction. Wind speed was recorded simultaneously at five heights. For 75 measurements of within-canopy wind speed profiles, the attenuation coefficient was 4.4 ± 0.5, a value typical for plant stands with very dense canopies. Video recordings proved that A. donax becomes streamlined with increasing wind speed, reducing the projected surface area of leaves and stem. The total projected surface area is a function of wind speed and can be characterized by a second-order polynomial regression curve. For small wind velocities up to 1 m/s, the calculated drag force is proportional to the square of the wind speed. However, when A. donax plants are subjected to higher wind speeds (1.5-10 m/s), the drag force becomes directly proportional to the wind speed. Streamlining is a potentially important adaptation for withstanding high wind loads, especially for individual plants and plants at the edge of stands, whereas in dense stands streamlining probably plays a minor role.     

In situ measurements of hydrodynamic forces imposed on Chondrus crispus Stackhouse

Among the hydrodynamic forces experienced by intertidal organisms, drag and the impingement force are thought to have the greatest effect on macroalgae. These forces are modified by biotic factors such as algal morphology, reconfiguration, and the presence of a canopy. However, much of what is known about the hydrodynamics of macroalgae has been garnered from low-velocity laboratory flume studies. Few field studies have measured drag and none have directly measured the effects of the canopy on force. To examine in situ hydrodynamic forces imposed on the turf forming macroalga Chondrus crispus, compact digital force sensors were developed that measure and record the 3-dimensional force imposed on a macroalga without disturbing the surrounding canopy. Sensors were positioned within natural Chondrus beds and the effects of the canopy, algal morphology, and sea state on in situ hydrodynamic force were examined. Additionally, the predictions of a new model for drag on flexible macroalgae were tested by simultaneously measuring force and water velocity. Digital force recordings indicated that Chondrus only experience drag; lift and impingement force were negligible in all combinations of factors. Canopies significantly reduced drag by 15-65%. Morphology and size also influenced drag, such that lower forces were imposed on small planar algae than large arborescent individuals. Further, planar algae experienced low drag in all combinations of sea and canopy state, indicating that these individuals may not be as susceptible to wave disturbance as arborescent individuals. Overall, these data indicate that the ability for Chondrus to grow large, arborescent individuals is dependent on the drag reducing properties of the canopy, while more hydrodynamically harsh habitats may be accessible to planar morphologies. Additionally, these data suggest that drag models for canopy forming macroalgae must incorporate the effects of the canopy to predict drag accurately in situ.     

Effect of leg kick on active drag in front-crawl swimming: Comparison of whole stroke and arms-only stroke during front-crawl and the streamlined position

The purpose of this study was to examine the effect of leg kick on the resistance force in front-crawl swimming. The active drag in front-crawl swimming with and without leg motion was evaluated using measured values of residual thrust (MRT method) and compared with the passive drag of the streamlined position (SP) for the same swimmers. Seven male competitive swimmers participated in this study, and the testing was conducted in a swimming flume. Each swimmer performed front-crawl under two conditions: using arms and legs (whole stroke: WS) and using arms only (arms-only stroke: AS). Active drag and passive drag were measured at swimming velocities of 1.1 and 1.3 m s⁻¹ using load cells connected to the swimmer via wires. We calculated a drag coefficient to compare the resistances of the WS, AS and SP at each velocity. For both the WS and AS at both swimming velocities, active drag coefficient was found to be about 1.6–1.9 times larger than that in passive conditions. In contrast, although leg movement did not cause a difference in drag coefficient for front-crawl swimming, there was a large effect size (d = 1.43) at 1.3 m s⁻¹. Therefore, although upper and lower limb movements increase resistance compared to the passive condition, the effect of leg kick on drag may depend on swimming velocity.     

Attachment strength of an adhesive nuisance mussel,limnoperna fortunei,against water flow

The attachment strength of the freshwater mussel Limnoperna fortunei against water flow was studied. Newton's expression successfully described the hydrodynamic drag force acting on the mussel with a drag coefficient value of 1.03. The drag‐resistant force (defined as hydrodynamic drag force at mussel detachment) was smaller than the detachment force measured using a tensile load test. A fairly good correlation was obtained between the drag‐resistant force and the number of secreted threads. The drag‐resistant force divided by the number of threads increased with shell size, suggesting that byssal thread strength increased with mussel growth. For the mussel specimens obtained from a water transmission pipe, thread width increased with shell size. However, thread width was not dependent on current velocity. There was no correlation between the number of secreted threads and shell length, which indicated that the number of secreted threads did not change with mussel size. Therefore, the water velocity needed to detach mussels increases with shell size of the mussel when the number of secreted threads is constant. The increases in the water velocity to detach mussels with larger shells suggests that the mussel becomes more resistant to water flow as it grows. It is estimated that a flow velocity of around lms^‐1 is critical for attachment/detachment of a juvenile mussel with a shell length of a few millimeters and one hundred byssal threads.     

Effects of exotic <Emphasis Type="Italic">Spartina alterniflora</Emphasis> on the habitat patch associations of breeding saltmarsh birds at Chongming Dongtan in the Yangtze River estuary,China

Smooth cordgrass (Spartina alterniflora) is one of the most invasive exotic plants of saltmarshes worldwide. To understand the effects of smooth cordgrass invasion on the habitat use and selection by breeding saltmarsh birds, we compared species number and abundance of breeding birds in native reed (Phragmites australis) and smooth cordgrass-invaded habitats (reed-cordgrass mixed habitats and cordgrass monocultures) at Chongming Dongtan in the Yangtze River estuary, China. We further examined the similarity of bird communities in different habitats and habitat selection by dominant bird species. For saltmarsh generalists, species number and abundance did not differ among the habitats. For saltmarsh specialists, species number and abundance did not differ in reed monocultures and reed-cordgrass mixed habitats but were significantly lower in cordgrass monocultures than in reed monocultures and reed-cordgrass mixed habitats. ANOSIM indicated that the difference in bird communities was larger between cordgrass monocultures and the habitats with reed than between the habitats with reed. The saltmarsh specialists preferred reed monocultures, while saltmarsh generalists avoided reed monocultures. Most species indicated no selection (neither preferred nor avoided) on reed-cordgrass mixed habitats, and no species preferred the cordgrass monocultures. The use of cordgrass monocultures by the common saltmarsh birds was negatively related to their body size. This study suggests that the spread of exotic smooth cordgrass has greatly affected the species composition and structure of local bird communities and has been especially disadvantageous to the saltmarsh specialists.     

Flow-induced forces on free-floating macrophytes

Free-floating macrophytes have buoyant petioles and unanchored roots; certain species are highly invasive, owing to characteristics such as high growth rates and the formation of dense floating mats that drift on wind and water currents. Water hyacinth (Eichhornia crassipes) is one example; its invasion of tropical and subtropical freshwater systems worldwide harms native ecosystems and impedes human activities. This research examines flow-induced forces and biomechanical properties of E. crassipes to better understand flow interactions and transport mechanisms. Drag forces were measured in a flume and a wind tunnel for varying approach velocities and raft configurations; from this data, drag coefficients in water (C _D^w) and air (C _D^a) were developed. Over similar Reynolds number (Re _b ) regimes, C _D^w decrease as Re _b increases while C _D ^a are invariant. For the same raft tested in air and water, water drag exceeds air drag and the value of C _D^w approaches C _D^a at high Re _b . Force–velocity relationships indicate root canopies reconfigure by streamlining in higher flow velocities while leaf canopies do not. Root canopy streamlining is further explained through biomechanical testing: we found the major vegetative structures of E. crassipes (roots, stolons, and petioles) have similar moduli of elasticity but second moments of area are three orders of magnitude smaller in roots compared to stolons or petioles, leading to significantly lower flexural rigidity in roots than in stolons or petioles. Flow interactions with the root canopy differ for an individual plant compared to a raft assemblage. Laboratory results suggest that water currents are the dominant mechanism for E. crassipes dispersal.     

Evapotranspiration,crop coefficient and water use efficiency of giant reed (Arundo donax L.) and miscanthus (Miscanthus × giganteus Greef et Deu.) in a Mediterranean environment.

Giant reed (Arundo donax L.) and miscanthus (Miscanthus × giganteus Greef et Deu.) are two perennial rhizomatous grasses (PRGs), considered as promising sources of lignocellulosic biomass for renewable energy production. Although the agronomic performance of these species has been addressed by several studies, the literature dedicated to the crop water use of giant reed and miscanthus is still limited. Our objective was thus to investigate giant reed and miscanthus water use by assessing crop evapotranspiration (ET_c), crop coefficients (K_c) and water use efficiency (WUE). The study was carried out in central Italy and specifically designed water-balance lysimeters were used to investigate the water use of these PRGs during the 2010 and 2011 growing seasons. Giant reed showed the highest cumulative evapotranspiration, with an average consumption of approximately 1100 mm, nearly 20% higher than miscanthus (900 mm). Crop evapotranspiration rates differed significantly between the species, particularly during the midseason (from June to September), when average daily ET_c was 7.4 and 6.2 mm in giant reed and miscanthus respectively. The K_c values determined in our study varied from 0.4 to 1.9 for giant reed and 0.3 to 1.6 for miscanthus. Finally, WUE was higher in miscanthus than in giant reed, with average values of 4.2 and 3.1 g L⁻¹ respectively. Further studies concerning water use under nonoptimal water conditions should be carried out and an assessment of the response to water stress of both crops is necessary to integrate the findings from this study.     

Miscanthus × giganteus and Arundo donax shoot and rhizome tolerance of extreme moisture stress

Crops grown for bioenergy production are a mandated component of the United States energy portfolio. Giant miscanthus (Miscanthus × giganteus) is a leading bioenergy crop similar in habit to the invasive plant giant reed (Arundo donax). To characterize the environmental tolerance of giant miscanthus, we compared the soil moisture stress tolerance of giant miscanthus and giant reed under glasshouse conditions. We subjected both species to soil moisture conditions of severe drought (?4.2 MPa), mild drought (?0.5 MPa), field‐capacity (control), and flooded soils. These conditions were applied to two cohorts: one in which soil moisture conditions were imposed on newly planted rhizome fragments, and one in which conditions were imposed on established plants after 8 weeks of growth in field‐capacity soil. After 16 weeks, we harvested all plants, measured above‐ and belowground biomass, and evaluated the reproductive viability of rhizome fragments. The total biomass of each species under flooded conditions was not different from the field‐capacity control groups regardless of cohort. However, drought did affect the two cohorts differently. In the cohort treated after 8 weeks of growth, mild and severe drought conditions resulted in 56% and 66% reductions in biomass, averaged over both species, compared with the controls. In the cohort treated for the entire 16 weeks, mild and severe drought conditions resulted in 92% and 94% reductions in biomass. Rhizome fragments from both species and both cohorts showed 100% viability following flooded and control treatments; drought treatments reduced rhizome viability in both species, with a greater impact on giant miscanthus. Although giant miscanthus does not appear to have the potential to escape and establish in relatively dry upland ecosystems, it does show tolerance to flooded conditions similar to giant reed.     

Assessment of Aboveground and Belowground Vegetative Fragments as Propagules in the Bioenergy Crops Arundo donax and Miscanthus × giganteus

Giant miscanthus (Miscanthus × giganteus) and giant reed (Arundo donax) are leading bioenergy crops. Both exhibit many invasive characteristics, though only giant reed is known to be invasive. Despite this, neither produces viable seed, limiting movement to vegetative propagules. Therefore, to assess vegetative fragments as potential propagules, we quantified seasonal changes in culm node viability and performance in giant miscanthus and giant reed under greenhouse conditions. Giant miscanthus culms were collected in spring, summer, fall, and winter from established fields, while giant reed culms were collected in summer, fall, and winter from feral stands. Treatments at each timing consisted of whole culms and single-node culm fragments planted in soil or placed in standing water for an 8-week period. Giant miscanthus whole culms and fragments produced shoots and roots in both soil and standing water immediately following cutting from spring to summer, but failed to produce shoots and roots after fall and winter cutting dates. All rhizome fragments survived and generated shoots and roots after burial. By comparison, giant reed produced shoots and roots in both soil and standing water throughout the year, regardless of cutting date. With giant miscanthus, precautions should be taken when living culms or rhizome fragments are harvested and transported through riparian habitats during the summer months. By comparison, giant reed showed a remarkable increase in propagule generation and productivity throughout the year and, thus, escaped propagules present a far greater risk of unintentional establishment compared to giant miscanthus.     

Myonemal contraction of spirostomum. II. Some mechanical properties of the contractile apparatus

In several respects, notably the high velocity of shortening, Ca²⁺ dependence, and ATP independence, contraction of Spirostomum resembles the spasmonemal mechanism of the peritrich ciliates. In this report further mechanical properties of the contractile apparatus are described that extend this comparison. The velocity-load characteristic is more appropriate to an elastomer than to a muscle where contraction force is load-dependent. Active tension is found to relate linearly to cell length for extensions up to and beyond resting length (l_r), an elastic limit is reached around 1.5 l_r. At resting length this tension, measured by the deformation of a glass microbalance, is similar to that predicted from consideration of the hydrodynamic forces normally resisting shortening. The tension-length relation for the unstimulated (passive) cell is also linear between l_r and the elastic limit, but is displaced from the active tension-length curve and is of reduced stiffness. Kinetic studies suggest that maximum tension and maximum velocity coincide. Calculations are presented that support a model of contraction in Spirostomum in which the myonemes behave as a mechanochemical engine powered directly by the chemical potential of Ca²⁺.     

Solute levels and osmoregulatory enzyme activities in reed plants adapted to drought and saline habitats

The pattern of solute accumulation and the activities of key enzymes involved in metabolism of proline and betaine were investigated in three ecotypes of reed from different habitats: swamp reed (SR), dune reed (DR), and heavy salt meadow reed (HSR). The two terrestrial reed ecotypes, DR and HSR, exhibited a higher capacity for osmotic adjustment; they accumulated higher contents of K⁺ and Ca²⁺ in the leaves in comparison with SR. DR also had the highest soluble sugar content in its leaves. HSR has higher levels of Na⁺ in its root environment and this was reflected by considerable accumulation of Na⁺ in the HSR rhizome. However, the different zones of its leaf lamina (upper, middle and lower) did not exhibit increased levels of Na⁺, suggesting that HSR has the ability to accumulate Na⁺ in the rhizome to protect the shoots from excessive Na⁺ toxicity. DR and HSR had higher levels of proline and betaine in the leaves than did SR. This difference was consistent with the activities of the various biosynthetic enzymes: betaine aldehyde dehydrogenase (BADH), pyrroline-5-carboxylate reductase (P5CR) and ornithine--aminotransferase (OAT) were enhanced in DR and HSR as compared to SR, whereas proline oxidase (PO) activities were inhibited. These findings suggest that changes in the activities of enzymes involved in osmotregulation might play important roles in the adaptation of reed, a hydrophilic plant, to more extreme dune and saline habitats. The relative contributions of the various proline synthetic pathways are also discussed.     

Geographic and environmental variation in Bryconops sp. cf. melanurus (Ostariophysi: Characidae) from the Brazilian Pantanal

Morphometric analyses of 220 specimens of a characid, Bryconops sp. cf. melanurus, from the Brazilian Pantanal were used to describe allometric growth in that species and determine whether specimens from highland habitats were more streamlined than those from lowland habitats. Relative warp analysis of 14 landmarks and principal component analysis of 28 interlandmark distances returned complementary results. The increased streamlining of the highland specimens is highly consistent with known inductive effects of high water velocity on fish phenotypes. Genetic differentiation and inductive effects of temperature variation are also potential explanations of the observed phenotypic differentiation.     

The Regulation of the Plasma Membrane Redox System and H+-transport in Adaptation of Reed Ecotypes to Their Habitats

The redox system and H⁺-transport activities in the plasma membranes from two ecotypes of reed (Phragmites communis Trin.), named swamp reed (SR) and dune reed (DR) according to their habitats, were investigated. Compared to the SR, the DR possessed the very high rates of NADH oxidation and Fe(CN)₆ ^3– and EDTA-Fe³⁺ reduction when NADH was taken as the electron donor. As NADPH was an electron donor, the rate of NADPH oxidation was also significantly higher in the DR than that in the SR. In addition, the H⁺-transport activity in the plasma membranes was also significantly higher in the DR than in the SR.     

Seasonal changes of polyamines in habitat adaptation of different ecotypes of reed plants

The leaves of four reed ecotypes (Phragmites communis Trinius) growing in the desert regions of northwest China were investigated for levels of polyamines and activity of arginine decarboxylase (ADC; EC 4.1.1.19) during the growing season of 5 months. The polyamines in the leaves of all reed ecotypes consisted of putrescine, spermidine and spermine. The polyamine levels of the leaves were lower in the swamp reed than in the terrestrial reed ecotypes. Leaf polyamine levels decreased in all ecotypes over the course of the season. Compared to the swamp reed, the terrestrial reed ecotypes maintained higher ADC activity and a predominance of spermine, resulting in a lower ratio of putrescine to spermidine and spermine. It seems that the adaptation of reed plants to drought and saline habitats may be correlated with putrescine synthesis via the ADC pathway, and with a successful conversion of putrescine to spermidine and spermine.     

Biomass Production and Composition of Perennial Grasses Grown for Bioenergy in a Subtropical Climate Across Florida, USA

Carbohydrate and lignin composition of feedstock materials are major factors in determining their bioenergy potential. This study was conducted to quantify dry biomass yield and the carbohydrate and lignin composition of six potential biofuel grasses (elephantgrass, energycane, sweetcane, giant reed, giant miscanthus, and sugarcane) across three sites in Florida for plant (2009) and first ratoon (2010) crops. Dry biomass yields ranged from about 30 to 50 Mg ha^?1 and were generally greatest for elephantgrass, energycane, sweetcane, and sugarcane. Accordingly, total plant carbohydrate yields (20 to 25 Mg ha^?1) were comparable among sugarcane, energycane, sweetcane, and elephantgrass, but were generally less for giant reed and even less for giant miscanthus. However, the contribution of total extractable carbohydrates and total fiber carbohydrates to total plant carbohydrate yields differed among species. Sugarcane had the highest concentrations of extractable carbohydrates (219 to 356 mg g^?1), followed by energycane, then sweetcane, elephantgrass, and giant reed, with giant miscanthus having the lowest. Energycane and elephantgrass tended to have significantly more fiber glucose, and elephantgrass less xylose, than other species. Variability in total lignin concentrations on a fiber basis was relatively modest (250 to 285 mg g^?1) across species, but was generally highest in sweetcane and giant reed. Overall, elephantgrass and energycane were prime regional candidates for cellulosic conversion using fermentation processes due to high yields and favorable fiber characteristics, although energycane tended to have higher extractable carbohydrates.     

Influence of NaCl-salinity on growth,photosynthesis, water relations and solute accumulation in <Emphasis Type="Italic">Phragmites australis</Emphasis>

The aim of this study was to investigate the effects of NaCl-salinity on the physiological attributes in common reed, Phragmites australis (Cav.) Trin. ex Steudel. Plants grew optimally under salinity treatment with standard nutrient solution without added salt and at NaCl concentrations up to 100 mM. Applied for 21 days, NaCl-salinity (300 and 500 mM) caused a significant reduction in growth allocation of all different tissues of P. australis. Shoot growth of reed plants displayed a highly significant correlation with plant–water relations and photosynthetic parameters. The net photosynthetic rate and stomatal conductance of reed plants treated with NaCl-salinity at varying osmotic potential (ψ_π) of nutrient solutions were positively correlated, and the former variable also had a strong positive relationship with transpiration rate. Leaf water potential and ψ_π followed similar trends and declined significantly as ψ_π of watering solutions was lowered. The increase in total inorganic nutrients resulting from increased Na⁺ and Cl⁻ in all tissues and K⁺, Ca²⁺ and Mg²⁺ concentrations were maintained even at the most extreme salt concentration. Common reed exhibited high K⁺/Na⁺ and Ca²⁺/Na⁺ selectivity ratios over a wide range of salinities under NaCl-salinity. These findings suggest that reed plants were able to adapt well to high salinities by lowering their leaf ψ_π and the adjustment of osmotically active solutes in the leaves.     

Water velocity regulates macro‐consumer herbivory on the benthic macrophyte Podostemum ceratophyllum Michx.

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