Growth and morphological responses to water level and nutrient supply in three emergent macrophyte species

Sanjiang Plain is the largest freshwater marsh in China, where plant zonation along water-level gradients is a common phenomenon. The aim of this experiment was to identify the role of water level and nutrient availability on plant zonation in the plain. Growth and root morphology of three perennial emergent macrophyte species were investigated by growing in two water levels (0.1 and 10.0 cm, relative to soil surface) and in two levels of nutrient supply (0 and 0.5 g slow-release fertilizer per container). In the plain, Carex lasiocarpa typically occurs at low elevations, Glyceria spiculosa at medial elevations, and Deyeuxia angustifolia at high elevations. The relative growth rate was the highest in C. lasiocarpa and the lowest in D. angustifolia in the 10.0-cm water level. Among the three species, only total biomass of D. angustifolia was affected by water level, and decreased with increasing water level. High nutrient supply led to increased total biomass in C. lasiocarpa and G. spiculosa. High water level led to an increased root diameter in G. spiculosa and a decreased root length in C. lasiocarpa. In the 10.0-cm water level, low nutrient supply led to thinner roots in D. angustifolia, but resulted in an increased specific root length (SRL) in C. lasiocarpa and root diameter in G. spiculosa. Water-level effect on root porosity was only observed in G. spiculosa, and nutrient amendment did not influence root porosity in all the species. These data indicate that both nutrient and water level are important factors regulating plant distribution pattern in the Sanjiang Plain, because both C. lasiocarpa and G. spiculosa are relatively sensitive to nutrient supply whereas D. angustifolia is sensitive to water level. Handling editor: S. M. Thomaz     

The influence of water level fluctuations on the potential for convective flow in the emergent macrophytes Typha domingensis and Phragmites australis

This paper examines the influence of the amplitude of water level fluctuations and elevation on the gas space anatomy and potential for convective flow in the emergent macrophytes Typha domingensis Pers. and Phragmites australis (Cav.) Trin. ex Steud. Plants were grown under a range of amplitudes of cyclic water level fluctuations: static, ±15, ±30 and ±45 cm. The water level of each treatment fluctuated around an initial and average depth of 60 cm. Within each amplitude treatment, plants were grown at three elevations: sediment surface 20, 40 and 60 cm above the base of the pond.The gas space anatomy of T. domingensis showed a range of modifications in response to experimental treatments. Lacunal cross-sectional area of the leaves increased with decreasing elevation as a product of changes in both fractional porosity and total cross-sectional area. Lacunal cross-sectional area of leaves was maintained across the gradient in amplitude through changes in fractional porosity despite decreasing total cross-sectional area. As a result of these adaptations in gas space anatomy, specific resistance in T. domingensis decreased with decreasing elevation but was unaffected by amplitude. In contrast, no unequivocal anatomical modifications were detected in P. australis and the specific resistance was constant across treatments.Estimates of the total resistance to convection in the above-ground parts of the plant suggests the adaptations in the gas space anatomy by T. domingensis largely compensated for increases in the pathlength of convection due to decreasing elevation. Total resistance increased significantly with increasing amplitude. P. australis had a low specific resistance which minimised the effect of increasing amplitude on total resistance but, lacking the ability to adapt gas space anatomy, the total resistance was strongly affected by elevation. The differential impact of elevation and amplitude suggests the two species have contrasting aptitudes for aeration across gradients in elevation and amplitude. T. domingensis is better suited to tolerate a range of static water depths whereas P. australis is better suited to fluctuating water levels especially when growing at high elevations.     

The influence of water level on macrophyte growth and trophic interactions in eutrophic Mediterranean shallow lakes: a mesocosm experiment with and without fish

1. Water‐level fluctuations are typical of lakes located in the semi‐arid Mediterranean region, which is characterised by warm rainy winters and hot dry summers. Ongoing climate change may exacerbate fluctuations and lead to more severe episodes of drought, so information on the effects of water level on the functioning of lake ecosystems in such regions is crucial. 2. In eutrophic Lake Eymir, Turkey, we conducted a 4‐month (summer) field experiment using cylindrical 0.8‐m‐ (low‐water‐level) and 1.6‐m‐deep (high‐water‐level) mesocosms (kept open to the sediment and atmosphere). Fish (tench, Tinca tinca, and bleak, Alburnus escherichii) were added to half of the mesocosms, while the rest were kept fishless. Ten shoots of Potamogeton pectinatus were transplanted to each mesocosm. 3. Sampling for physicochemical variables, chlorophyll a (chl‐a), zooplankton and per cent plant volume inhabited (PVI%) by macrophytes was conducted weekly during the first 5 weeks, and subsequently biweekly. Macrophytes were harvested on the last sampling date. During the course of the experiment, the water level decreased by 0.41 ± 0.06 m. 4. Throughout the experiment, fish affected zooplankton abundance (?), nutrient concentrations (+), chl‐a (+) and water clarity (?) most strongly in the low‐water‐level mesocosms and the zooplankton community shifted towards dominance of small‐sized forms. The fishless mesocosms had a higher zooplankton/phytoplankton ratio, suggesting higher grazing. 5. Greatest macrophyte growth was observed in the low‐water‐level fishless mesocosms. However, despite high nutrient concentrations and low water clarity, macrophytes were also abundant in the fish mesocosms and particularly increased following a water‐level decrease from midsummer onwards. Macrophyte growth was poor in the high‐water‐level mesocosms, even in the fishless ones with high water clarity. This was ascribed to extensive periphyton development reducing light availability for the macrophytes. 6. Our results indicate that a reduction in water level during summer may help maintain the growth of macrophytes in Mediterranean eutrophic shallow lakes, despite a strong negative effect of fish predation on water clarity. It is therefore probable that an expected negative effect of global climate change on water clarity because of eutrophication and enhanced top‐down control of fish may be, at least partly, counteracted by reduced water level, provided that physical disturbance is not severe.     

Plant distribution can be reflected by the different growth and morphological responses to water level and shade in two emergent macrophyte seedlings in the Sanjiang Plain

In the Sanjiang Plain (North East China), narrowleaf small reed (Deyeuxia angustifolia) usually distributes widely in typical meadow or marsh, while reed (Phragmites australis), the concomitant species, is distributed sparsely in the D. angustifolia communities or relative open sites. To date, the mechanisms responsible for their different distribution patterns are far from clear. Both water level and light are important factors determining plant distribution in wetland ecosystems and therefore, the aim of this paper was to identify the role of these two factors and their potential interaction on plant distribution in this plain. Growth responses and biomass allocation of the two macrophytes were investigated by growing them in three irradiances (300, 100, 20 μmol m⁻² s⁻¹) and two water levels (0 and 5 cm) under greenhouse conditions. Biomass accumulation, mean relative growth rate (RGR), height and mean relative elongation rate (RER) of both species significantly decreased with the reduction of light availability. Biomass accumulation, RGR, height and RER of P. australis were significantly inhibited by higher water level. However, water level had no effect on the growth of D. angustifolia. Stem mass fraction was higher at 0-cm water level in D. angustifolia, and was not affected by water level in P. australis. These data suggest that D. angustifolia has a higher adaptive ability to acclimate to flooding and shade stresses than does P. australis, which might be an important reason for their different distribution patterns.     

The effect of water level fluctuations on a littoral fauna

The littoral fauna of Llyn Tegid, North Wales, in 1968/9 is compared with the results of similar faunal investigations made by Rothwell(née Dunn) in 1951/2 (Dunn, 1953) and Hynes in 1957 and 1959 (Hynes, 1961). The results show the long term effects upon the littoral fauna of the change in mean water level and the increased water level fluctuations produced for a time by the controlled outflow scheme, which came into operation in 1955. In 1961 Hynes recorded big reductions in numbers and variety of invertebrates living in the littoral zone. The reduced water level fluctuations in recent years has resulted in a re-establishment of some of the fauna.     

The influence of ventilation systems on water depth penetration of emergent macrophytes

1. Roots of emergent macrophytes depend on oxygen transported from aerial parts by diffusion and, in some species, by pressurised ventilation. The aim of this study was to determine if species with pressurised ventilation grow in deeper water in situ than species lacking this ability.
2. Species with pressurised ventilation grew significantly deeper than species lacking pressurised ventilation, and this was true in substrates with low as well as high redox potential.
3. Two species with low or non-detectable flow rates ( Schoenoplectus lacustris and Equisetum fluviatile , respectively) were found in unexpectedly deep water. Thus, pressurised ventilation is not a prerequisite for growth in deep water. It is, however, suggested that species with pressurised ventilation have a competitive advantage in deep water resulting in long-term competitive exclusion of species lacking pressurised ventilation.     

The effect of spring water on the growth of a submerged macrophyte Egeria densa

We elucidated the effect of spring water on the growth of Egeria densa Planch., a widespread submerged macrophyte in Japan. We observed the longitudinal distributions of physical (water temperature, particle diameter of the bed sediment, sediment layer thickness, etc.), chemical [pH, dissolved oxygen (DO), dissolved inorganic carbon (DIC), phosphate (PO₄-P), total nitrogen (TN), and total phosphorus (TP) content of the sediment, etc.], and biological (species composition, biomass, and growth rate) factors related to E. densa in the Kurohashi River, a spring-fed stream flowing into the Lake Biwa. It was found that E. densa growth rate from summer to autumn was negatively correlated to pH and DO, which implies that the low pH spring water increases the growth rate of the species. The growth rate was also positively correlated to the free carbon dioxide (CO₂) concentration (r = 0.67, p = 0.02). These results indicate that the low pH spring water increases E. densa growth rate by affecting free CO₂ concentration in water.     

Ephemeral saline lakes on the Canadian prairies: their classification and management for emergent macrophyte growth

At two ephemeral saline lakes in Saskatchewan, changes in the physical and chemical features of water and sediments at various basin positions were monitored during a wet-dry cycle in 1978 and 1979. Water salinity fluctuated widely in response to changes in water volume and mass of solute in the water. When basins were dry, the soluble salt content of sediments 0–10 cm deep was higher than sediments 50–60 cm deep and sediments in the lake centre were more saline than at the shoreline. Upon reflooding, there was a large immediate decrease in sediment salinity at the 0–10 cm depth, such that this layer was less saline than sediments 50–60 cm deep. Sediments in the lake centre remained more saline than at the shoreline.Classification of lake salinity is necessary to assess the potential of a lake for emergent production. The large variances in ephemeral lake salinity due to water volume changes indicate that classification should be based upon the water volume-salinity cycle of these lakes rather than the salinity of any single water or sediment sample. Water management efforts to lower salinities, to improve these wetlands for emergent growth, should be aimed at reducing the salinity regime of the littoral zone. Flushing, dilution and drying and reflooding techniques are discussed as methods to decrease salinity.     

Phosphorus fluctuation in water and deposition into sediment within an emergent macrophyte stand

Seasonal fluctuation of phosphorus in water, and total phosphorus and different inorganic P fractions (extracted by NH₄Cl, NH₄F, NaOH and H₂SO₄) and organic P fraction (residual P) in surface sediment, were measured in the littoral of oligotrophic Lake Pääjärvi (southern Finland). After the emergence of Equisetum fluviatile L. shoots in mid June, water exchange between the littoral and pelagial area diminished and phosphorus concentrations in water and in surface sediment increased in the inner and mid littoral zones. Phosphorus pool in flocculent, easily resuspensible sediment composed on average 62% of inorganic phosphorus and 38% of organic phosphorus. 63% of the inorganic phosphorus, on the average, was extracted from apatite-P fraction 29% from iron-P fraction 7% from aluminum-P fraction and less than 1% from loosely-bound P fraction. During the growing season, net accumulation of sediment and phosphorus was measured only in the inner littoral zone whereas the outer littoral zones acted rather as a source of phosphorus for the pelagic area. The results of this study indicated that nutrient dynamics in littoral environment was through changes in flow environment greatly governed by the macrophytes.     

Transpiration by an emergent macrophyte: source of water and implications for nutrient supply

The contribution of sediment interstitial water and the water column to the transpiration stream of Myriophyllum aquaticum (Vellozo) Verdcourt was determined to estimate the significance of mass flow in supply of sediment nutrients for plant growth. Sediment interstitial water accounted for about 2% of the water transpired over a 37 day period. Because of the small volume of water that originated in the sediment we concluded that mass flow did not significantly enhance nutrient supply to the roots of M. aquaticum. Relative growth rate (RGR) of adventitious, water roots was greater than whole plant RGR, and RGR of sediment roots was not significantly different from zero, indicating a shift in the biomass allocation after emergence of the apical meristem into the air. Water use, measured by the transpiration coefficient, averaged 260 ml H₂O mg DW^-1, which is similar to C-4 terrestrial plants. M. aquaticum has leaf characteristics commonly associated with xerophytic habitats. These characteristics may be necessary if a high transpiration rate and a mechanical requirement for high cell turgor pressure, required by a reliance upon hydrostatic pressure for support of the aerial stems, are mutually exclusive because of morphological constraints on hydraulic conductivity.     

Effects of the emergent macrophyte Juncus effusus L. on the chemical composition of interstitial water and bacterial productivity

Release of oxygen from the roots ofaquatic macrophytes into anaerobic sediments canaffect the quantity of interstitial dissolved organicmatter and nutrients that are available to bacteria. Nutrient and dissolved organic carbon (DOC)concentrations were compared between subsurface(interstitial) waters of unvegetated sediments andsediments among stands of the emergent herbaceousmacrophyte Juncus effusus L. in a lotic wetlandecosystem. Concentrations of inorganic nitrogen(NH₄⁺, NO₃^-, and NO₂^-)were greater from sediments of the unvegetatedcompared to the vegetated zone. DOC concentrations ofinterstitial waters were greater in sediments of theunvegetated zone both in the winter and springcompared to those from the vegetated zone. AlthoughDOC concentrations in hydrosoils collected from bothzones increased from winter to spring, bacterialproductivity per mg DOC in spring decreased comparedto winter. Greater initial bacterial productivityoccurred on DOM collected from the vegetated comparedto the unvegetated zone in winter samples (days 1 and4), with increased bacterial productivity on samplescollected from the unvegetated zone at the end of thestudy (day 20). Bacterial productivity wassignificantly greater on all sampling days on DOM fromvegetated samples compared to unvegetated samples. In nutrient enrichment experiments, bacterialproductivity was significantly increased (p < 0.05)with phosphorus but not nitrogen only amendments.     

Seasonal fluctuations in macrophyte cover and water transparency of four brown-water lakes: implications for crustacean zooplankton in littoral and pelagic habitats

The dynamics of crustacean zooplankton in the littoral and pelagic zones of four forest lakes having variable water qualities (colour range 130–340 mg Pt l⁻¹, Secchi depth 70–160 cm) were studied. The biomass of zooplankton was higher in the littoral zone than in the pelagic zone only in the lake having the highest transparency. In the three other lakes, biomass was significantly higher in the pelagic zone than in the littoral zone. In the two lakes with highest transparency, the littoral biomass of cladocerans significantly followed the development of macrophyte vegetation, and cladoceran biomass reached the maximum value at the time of highest macrophyte coverage. In lakes with lowest transparency, littoral zooplankton biomass developed independently of macrophyte density and decreased when macrophyte beds were densest. The seasonal development of the littoral copepod biomass did not follow the development of macrophytes in any of the lakes. The mean size of cladocerans in the pelagic zone decreased with increasing Secchi depth of the lake, whereas in the littoral zone no such phenomenon was detected. Seasonally, when water transparency increased temporarily in two of the lakes, the mean size of cladocerans in the pelagic zone decreased steeply. For copepods, no relationship between water transparency and body size was observed. The results suggested that in humic lakes the importance of the littoral zone as a refuge decreases with decreasing transparency of the water and that low water transparency protects cladocerans from fish predation. All the observed between-lake differences could not be explained by fish predation, but were probably attributed to the presence of chaoborid larvae with variable densities. Feeding efficiency of chaoborids is not affected by visibility and thus they can obscure the relationship between water quality, fish density, and the structure of crustacean zooplankton assemblages. Handling editor: S. I. Dodson     

Two forms of adventitious growth on fertile shoots of the emergent macrophyte, Juncus militaris bigel.

Adventitious growth was observed on fertile shoots of Juncus militaris Bigel. (bayonet rush) growing in Rhode Island freshwater lake during a summer of high water levels. Adventitious roots appeared at involucral bract nodes, and adventitious vegetative propagules appeared on inflorescence axes. The adventititious vegetative propagules became detached from the inflorescence axes and were transported to shore by wind and wave action.     

The boundary filtration effect of reed-dominated ecotones under water level fluctuations

The boundary filtration effect of land/water ecotones with reed-bed/ditch systems under water level fluctuations was studied in Baiyangdian Lake of North China. It was found that the changes in reed bed areas which were primarily affected by water level fluctuations and the root channels in the wetland soils together largely determined boundary filtration efficiency. The ecotones displayed the greatest boundary effect at a moderate water level of about 8 m above sea level. The massive root channels in the wetland soils promoted water flowing into the reed beds as far as 8 m horizontally by subsurface in wet years. In dry years, when the water level was below the root channel distribution zone, the lateral water exchange width of ecotones was limited to 0.5 m along the fringe area. It is calculated that, at 8 m water level, the total boundary length of ecotones is 7,273 km and the boundary exchange volume is 5.8 × 10⁶ m³. While at 6.5 m water level, the total boundary length of ecotones is reduced to 2,699 km and the boundary exchange volume is 1.1 × 10⁵ m³. The standard capacity for phosphorus retention was 105.9 and 2.5 tonnes at water levels of 8 and 6.5 m, respectively. This suggests that the boundary filtration effect of reed-bed/ditch wetlands is important for improving the water quality of inland waters, and this effect should be considered in regulating and managing lake water levels.     

The influence of large water level fluctuations and hurricanes on periphyton and associated nutrient storage in subtropical Lake Okeechobee,USA

The abundance, community structure and nutrient content of periphyton, and the host plant taxa Chara, Hydrilla, Potamogeton, Vallisneria and Scirpus were studied in Lake Okeechobee, USA. Water levels were generally high during the study period (August 2002–January 2006), but substantial fluctuations occurred. All host plant biomass was seasonally variable but only Vallisneria biomass was spatially variable. All submerged plant beds disappeared after the passage of two hurricanes in September 2004, and a third hurricane passed over the lake in October 2005. Periphyton assemblages were statistically separated most by substrate and then by season. Prior to the hurricanes, annual maxima of periphyton biovolumes and those of summer submerged plant coverage coincided. During all study years, the diatom taxa dominated periphyton total biovolumes. Periphyton biomass was generally highest during the summer or prior to the hurricanes (in the case of epiphytes) and was spatially variable in the case of both Scirpus and Vallisneria. Epiphytic nutrient contents within each host plant group seasonally varied except for nitrogen and carbon in the Vallisneria epiphytes. Epipelic nutrient contents were spatially variable and seasonally variable for carbon. Nutrient contents in epipelon were significantly higher than that in Scirpus epiphytes and were similar but lower among all epiphytic communities. The total annual areal potential epiphytic phosphorus storage extrapolated during this study (2.0 × 10⁻⁴ metric tons ha⁻¹ year⁻¹) was underestimated because storage estimates for epipelon, Chara and Hydrilla-associated epiphytes were omitted. The Chara and Hydrilla-associated epiphytic nutrient storage values were omitted because of limited data, whereas the epipelic data may have not been spatially representative. For periphyton biovolume, host substrate type, water level fluctuation and hurricane impacts on host substrates appear to be more important than seasonal variation in such factors as temperature and nutrients. Epiphytic nutrient storage appears to be influenced most by water level fluctuation and hurricane-related impacts, while the host substrate type appears to be a less important factor than it is for periphyton biovolume. Maximum periphyton biomass and high nutrient storage in shallow subtropical and tropical eutrophic lakes may only occur at consistently lower water levels and during infrequent periods of disturbance, which enhance host substrate colonizable area.     

On the water relations of four heath species

Four species of heath, occurring in the heathlands of Brittany, are compared regarding their water relations: Calluna vulgaris, Erica ciliaris, E. cinerea and E. tetralix. E. cinerea is unable to establish itself in wet heathland because of its intolerance of prolonged waterlogging. It is the Erica species best adapted to dry habitat conditions in Brittany. E. ciliaris canot establish itself in dry heathland and is less tolerant of waterlogging than E. tetralix. E. tetralix is the species best adapted to wet heathland, being tolerant of waterlogging, but can also establish itself in dry heathland. Of the three E. species it has the widest ecological range. Calluna is tolerant of both wet and dry conditions and has a wide ecological range. E. cinerea is typical of dry- and E. tetralix of wet heathland. Although both species did best in moist aerated soil in experimental cultures, neither is abundant in mesophilic heaths where E. ciliaris is dominant. One explanation may be competition for aerial space. E. cinerea and E. tetralix both have an upright growth, whereas E. ciliaris rapidly adopts a straggling bushy habit, with long rooting branches. E. ciliaris thus establishes large interpenetrating clumps. With increasing dryness E. ciliaris disappears and may be replaced by E. cinerea and, with increasing wetness and especially waterlogging, E. tetralix will take over.     

The influence of water level on the growth and photosynthesis of Hydrocotyle ranunculoides L.fil.

Floating Pennywort (Hydrocotyle ranunculoides L.fil.), a native to North America and naturalized in Central and South America, is an invasive aquatic weed in western Europe and several other regions worldwide. H. ranunculoides settles primarily in stagnant to slow-flowing waters (e.g. ditches, canals, rivers, lakes and ponds). The species prefers sunny and nutrient-rich sites and forms dense interwoven mats, which can quickly cover the surface of infested waters. In this study, the effect of three different water levels on growth of Floating Pennywort was investigated. Plants were cultivated on high-nutrient soils under waterlogged, semi-drained and drained conditions. Highest relative growth rates (RGR) of 0.097±0.004 g g⁻¹ dw d⁻¹ were reached under waterlogged conditions. This was significantly higher than RGR of plants cultivated semi-drained and drained. Floating Pennywort showed some phenological adaptations to drained soil conditions, including significant differences in the relative amounts of leaf, petiole and shoot biomass, whilst the relative amount of root biomass was not significantly influenced by the water level. Furthermore, Floating Pennywort reached under drained conditions lower relative water contents (RWC) of leaves, petioles and shoots, a significant shorter length of internodes, a significant lower extent of shoot porosity (POR), a lower chlorophyll content and an increased Chl_a:Chl_b ratio. In addition, maximum gas exchange of drained cultivated plants is significantly lower, due to strongly decreased leaf conductance under reduced water availability. Overall, H. ranunculoides showed ability to grow under different water levels, but performed best under waterlogged conditions.     

Habitat level determinants of emergent macrophyte occurrence,extension and change in two large boreal lakes in Finland

Historical (1947–1950) and present day (1998–2000) aerial photograph data of aquatic vegetation were combined with soil, land use and habitat morphology variables in two lakes, oligotrophic L. Näsijärvi (256 km²) and eutrophic L. Pyhäjärvi (122 km²), with regulated water levels in southern Finland. Multivariate GLM analyses were used to examine the determining factors of occurrence and horizontal extension of vegetation, occurrence of common reed (Phragmites australis) and water horsetail (Equisetum fluviatile) and the vegetation change in 474 sites. Despite differences in geography and water level regulation between the lakes, congruent trends were identified. The vegetation occurrence in both lakes had a positive response to clay soils and incoming nutrients and a negative response to housing and shore slope. Moraine soils, housing and shore slope had a negative effect on horizontal extension of vegetation in both lakes. The occurrence of P. australis was controlled by a negative response to moraine and the occurrence of E. fluviatile to slope in both lakes. The vegetation change in both lakes was characterized by a negative response to housing and slope.