Distribution and habitat of JapanesePotamogeton

The geographical distributions and habitats of JapanesePotamogeton were studied by extensive field survey throughout Japan. According to the distribution pattern, the species were classified into 3 groups: (1) the species widespread throughout Japan, (2) the ones distributed in northern Japan and (3) the ones distributed in central to south-western Japan. The habitats of each species were investigated in relation to water body type and pH, alkalinity, Ca⁺⁺, Cl^? and conductivity of water. Flow condition and the degree of water level fluctuation seemed to be important habitat factors affecting the occurrence of some species. Each species had its preference regarding the five chemical parameters of water. Especially, significance of alkalinity is discussed in relation to the inorganic carbon contents of water. Interspecific associations were examined. Floating-leaved species were shown to be mutually exclusive. Submerged species showed somewhat intricate associations. Also it was remarkable that, while in lentic environments 29 pairs with significant associations were revealed, only 2 pairs were significantly associated in lotic environments.     

Species richness of aquatic macrophyte communites in Central Canada

Aquatic macrophyte species richness (SR) was examined at 430 sites in the central Canadian region in relation to water body type, bottom substrate and 8 water chemistry parameters. SR was highest in rivers and lakes, intermediate in creeks, and lowest in ponds. The highest values occurred where granitic bedrock, highly organic substrates or sand predominated. SR was significantly inversely correlated in the study area as a whole with 7 of the water chemistry parameters; of these, total alkalinity was the most important. However, the relative importance of the respective parameters differed for various water body types. The relationship between SR and phosphorus was positive in ponds, but negative for all other water body types. Stepwise sultiple regression analysis identified phosphorus, total alkalinity and dissolved organic matter as important factors in ponds; sulphate, total alkalinity and chloride in lakes, and sulphate and phosphorus in lotic habitats. Log transformations improved the correlations for some variables. However, the water chemistry parameters examined accounted for less than half of the total variability in SR. Apparently SR depends on many different factors, including surface areaand bottom type, whose relative contributions vary with situation.     

On body size and habitat selection in rotifers in a macrophye-dominated lake Budzyńskie,Poland

Lake Budzyńskie is shallow, freshwater lake with a well-developed and differentiated macrophytic vegetation. Zooplankton samples were collected from five stations: two of them in submerged macrophytes (Chara and Myriophyllum), one in the zone of floating leaves (Potamogeton), a rush station (Typha) and one in the open water surrounding the vegetation beds. The mean Rotifera densities differed significantly between the lake parts. Furthermore, different habitats were characterised by differences in body size with the exception of the middle body size group (Keratella cochlearis, Polyarthra vulgaris and Trichocerca similis), which was dominated by limnetic representatives. However, in all the other size-dependent groups both stands of submerged macrophytes were characterised by much higher densities than other zones. Additionally, body size within the examined habitats significantly differed. Thus, the size structure of Rotifera communities was directly related to morphological and spatial structures of the substrata. Two groups of habitats were distinguished: the first one consisting of open water and two vegetated zones of less complicated structure (Potamogeton and Typha), and the second of more complex submerged macrophyte species (Chara and Myriophyllum). The differentiation of the architecture of macrophytes affected the nutritional conditions and refuge effectiveness of these habitats.     

Phylogenetic relationships and hybrid origin of Potamogeton species (Potamogetonaceae) distributed in China: insights from the nuclear ribosomal internal transcribed spacer sequence (ITS)

Hybridization and polyploidization are important evolutionary processes in higher plants and have greatly enriched the diversity of the genus Potamogeton (Potamogetonaceae). To study the phylogenetic relationships and hybrid origin of Potamogeton species, 35 accessions representing 20 species, including diploids, tetraploids and hexaploids, and three hybrids were collected in China and their ribosomal internal transcribed spacers (ITS) were cloned, sequenced and statistically analyzed. The data showed that ITS sequences were informative to analyze the phylogeny of Potamogeton, and the phylogenetic tree revealed that Potamogeton species examined could be mainly divided into two groups (Group I and II), corresponding to subgenus Potamogeton and subgenus Coleogeton, respectively. Then, the evolutionary mechanism on the polyploidy of Potamogeton species was discussed. P. natans probably was an allotetraploid and one of its parent might result from aneuploidy change of species with 2n=28. P. hubeiensis might be derived from the hybridization between P. octandrus and P. cristatus. We suggested that both P. lucens and P. maackianus probably were allotetraploids, and P. obtusifolius might be a diploid hybrid between P. compressus and P. pusillus. Moreover, P. malainoides might have undergone biased concerted evolution toward one of its parent P. wrightii, and P. intortusifolius might be a synonymy of P. × anguillanus.     

Photosynthetic carbon sources in somepotamogeton species

The ability of somePotamogeton species to use bicarbonate for photosynthesis was assayed by means of relative net photosynthetic rates in alkaline (bicarbonate) and acid (free CO₂) solutions with an equivalent amount of inorganic carbon. The results showedPotamogeton crispus, P. oxyphyllus, P. maackianus, P. perfoliatus, P. malaianus and the submerged leaves ofP. distinctus to be able to use bicarbonate ions for photosynthesis. To the contrary, the submerged leaves ofP. fryeri, which is an inhabitant of soft and acid waters, and the floating leaves ofP. distinctus were proven to be ‘non-users’ of bicarbonate ions. Furthermore, the relative photosynthetic rates were determined using natural waters with various carbon conditions. The dependence of photosynthetic performance on the free CO₂, pH and alkalinity of the waters is discussed in relation to carbon metabolism. Further it is suggested that the carbon conditions are ecologically significant in relation to the productivity and success of macrophyte species in natural habitats.     

Clonal growth architecture and spatial dynamics of 10 species of the genus <Emphasis Type="Italic">Potamogeton</Emphasis> across different habitats in Kashmir Valley,India

The plasticity in clonal architecture may enable plants to effectively respond to environmental constraints and to enhance species ecological niche breadth but its role in plant tolerance to water flow is poorly documented. The present study was carried out to determine whether the clonal architecture varies with respect to water flow in 10 species of the genus Potamogeton colonizing habitats differing by flow conditions. For these 10 species, the traits describing clonal architecture were measured on individuals sampled in natural sites and plasticity in clonal architecture was examined in a common garden growth experiment. The clonal growth architecture did not vary significantly in the species which inhabit either standing (P. lucens, P. natans, and P. pusillus) or running water (P. amblyphyllus and P. berchtoldii). However, the species inhabiting both standing as well as running waters (P. crispus, P. nodosus, P. pectinatus, P. perfoliatus, and P. wrightii) showed considerable and significant variation in clonal growth architecture across these habitats. Transplantation experiment revealed that clonal architecture observed between the plants under different conditions is plastic and not due to genetic differentiation. The present study demonstrated that plasticity in the clonal architecture may enable these species to inhabit stressful conditions of flowing water.     

The Relationships Between Environmental Factors and the Submerged Potametea Associations in Lakes of North-eastern Poland

A comparative analysis of submerged Potametea communities in lakes of north-eastern Poland was conducted with respect to 16 water chemistry and 14 substrate parameters. The analysis of 187 relevés based on TWINSPAN clustering showed the existence of 8 aquatic vegetation types. Each of them is characterized by a strong dominance of one of the following macrophytes: Potamogeton lucens, P. perfoliatus, Myriophyllum spicatum, M. verticillatum, Elodea canadensis, Ceratophyllum demersum, Ranunculus circinatus and Hydrilla verticillata. The above vegetation types correspond to the plant associations distinguished using the Braun-Blanquet method (Potametum lucentis, Potametum perfoliati, Myriophylletum spicati etc.) It was demonstrated that among properties of water analysed, COD-KMnO₄, SO₄²⁻, pH, Na⁺, K⁺, Ca²⁺, total hardness, total Fe, Cl⁻ and colour appear to be most important in differentiating the habitats of the communities studied. In the case of substrates the properties which best differentiated the habitats compared were hydration, organic matter content, total N, PO₄³⁻, K⁺, dissolved SiO₂, SO₄²⁻, Cl⁻ and pH. Most of the aquatic plant communities investigated are distinct with respect to their phytocoenotic structure and ecology and could be good indicators of various types of habitats in lake ecosystems.     

Habitat use and feeding behavior of thirteen species of benthic stream fishes

Synopsis The densities, habitat use, and feeding behaviors of 13 fish species belonging to the benthic invertebrate-feeding guild were studied by snorkeling at three localities in the Little River of eastern Tennessee, U.S.A. Resource partitioning occurred by habitat, feeding behavior and time of activity. Differences were also found at the generic level.Cottus was a nocturnal feeder, whereasPercina andEtheostoma were, for the most part, diurnally active.Percina moved about rapidly and spent most of its time above the bottom. In contrast,Etheostoma varied considerably in the amount of time spent under cover, spent little time above the bottom, and exhibited low levels of swimming activity. Nearly all species sought cover at night, suggesting they may be particularly sensitive to predation at night. Species with small adult sizes (Etheostoma, Cottus andP. evides) were concentrated in shallow water habitats, whereas species with large adult sizes (Percina) were more abundant in deep water habitats. The habitat use data are consistent with the hypothesis that size-selective predation by centrarchid bass may cause smaller fish to avoid deep water areas. Large species should have a lower risk of predation due to their size and behavior.     

Invasion of alien macroalgae in different Mediterranean habitats

The study evaluated different macroalgal invasions in the main Mediterranean coastal habitats on hard bottom. Biodiversity, species composition and structure of macroalgal assemblages were compared among non-invaded areas and areas invaded by the Chlorophyta Caulerpa racemosa var. cylindracea and by the turf-forming Rhodophyta Womersleyella setacea in three different habitats: shallow rocky bottom, deep rocky bottom and dead matte of the seagrass Posidonia oceanica. Results showed that alien macroalgae constituted a relevant component of benthic assemblages in invaded areas of the Mediterranean Sea. Assemblages invaded by Womersleyella setacea and Caulerpa racemosa showed lower values of diversity and large differences in the structure and species composition related to non-nvaded assemblages. The species that mostly suffered from invasion were erect species reproducing sexually; moreover, the dominance of W. setacea led to low abundance of native filamentous algae, while C. racemosa colonization seemed particularly threatening for encrusting algae. All the studied habitats appeared highly invasible by alien macroalgae, even if W. setacea appeared more invasive in deeper habitats, while colonization of C. racemosa seemed more serious in shallower habitats; the dead matte of P. oceanica represented a suitable substrate for the spread of both species. Differences among assemblages in different habitats were reduced in invaded areas.     

Life on the edge: hydrogen sulfide and the fish communities of a Mexican cave and surrounding waters

Most eucaryotic organisms classified as living in an extreme habitat are invertebrates. Here we report of a fish living in a Mexican cave (Cueva del Azufre) that is rich in highly toxic H₂S. We compared the water chemistry and fish communities of the cave and several nearby surface streams. Our study revealed high concentrations of H₂S in the cave and its outflow (El Azufre). The concentrations of H₂S reach more than 300 μM inside the cave, which are acutely toxic for most fishes. In both sulfidic habitats, the diversity of fishes was heavily reduced, and Poecilia mexicana was the dominant species indicating that the presence of H₂S has an all-or-none effect, permitting only few species to survive in sulfidic habitats. Compared to habitats without H₂S, P. mexicana from the cave and the outflow have a significantly lower body condition. Although there are microhabitats with varying concentrations of H₂S within the cave, we could not find a higher fish density in areas with lower concentrations of H₂S. We discuss that P. mexicana is one of the few extremophile vertebrates. Our study supports the idea that extreme habitats lead to an impoverished species diversity.     

Maternal effects and ecological divergence in aquatic plants: a case study in natural reciprocal hybrids between Potamogeton perfoliatus and P. wrightii

When parental taxa are adapted to different habitats, hybrid genotypes are often highly heterogeneous, such that habitat or ecological factors influence hybrid fate and ecological performance. Trait expression in hybrids is not always intermediate between the parents, but may instead be either parental‐like or extreme (transgressive) depending on genetic control of the phenotypes. Maternal effects arising from interspecific interaction between cytoplasmic and nuclear genomes are widely recognized as playing a role in character expression of natural hybrids. Such interaction often leads to hybrid sterility or inviability. When hybrids are viable, however, cytonuclear interaction may contribute to hybrid persistence through its influence on trait expression. To date, maternal influence on hybrid performance has been examined primarily in experimentally produced hybrids, or in natural hybrids without identification of the cross direction owing to difficulty in obtaining species‐specific molecular markers. In aquatic plants, many hybrids persist by extensive clonal growth and are important components of aquatic communities. Many such hybrids are known in Potamogeton (pondweeds), the largest aquatic genus. Because Potamogeton species are ecologically highly diverse and maternal lineages are readily distinguished using molecular markers, natural hybrids of Potamogeton are well‐suited for studies of maternal effects, especially those affecting vegetative performance. As a case study, we have focused on maternal effects on drought tolerance and depth distribution in the natural hybrid P. × anguillanus derived from the closely related species P. perfoliatus and P. wrightii.     

Measures to develop a rich-fen wetland landscape with a full range of successional stages

Species-rich plant communities characteristic for succession from mesotrophic open water to fen are very rare in The Netherlands. These vegetation types used to occur in turf ponds in the low lying peatland area, created by peat dredging and filled with water due to seepage of mesotrophic, well-buffered groundwater. One of the goals of the National Nature Policy Plan is to create new opportunities for the initial terrestrialization communities through ecological engineering, e.g., restoration and creation of open water habitats. Restoration of the abiotic conditions in acidified floating fen communities is only possible by a combined measure of removal of the Sphagnum-layer and superficial drainage of surplus rain water. New turfponds have been excavated. This study showed that the abiotic conditions (i.e., water depth and water chemistry) are favorable for the development of aquatic communities characteristic of mesotrophic conditions. The aquatic plant species found in the new ponds also point in this direction, e.g., Chara major and Ch. delicatula are very abundant as are seven Potamogeton species. It is concluded that a constant discharge of groundwater and a good connectivity between the ponds and the existing remnants of plant communities desired in the area are essential for the conservation and development of these species-rich plant communities.     

BIOCHEMICAL HETEROPHYLLY AND FLAVONOID EVOLUTION IN NORTH AMERICAN POTAMOGETON (POTAMOGETONACEAE)

Morphologically heterophyllous species of Potamogeton also commonly display biochemical heterophylly with respect to flavonoid compounds. Generally, floating leaves contain an assortment of flavonoids, whereas submersed leaves often exhibit reduced flavonoid profiles. In strictly submersed (homophyllous) species, two patterns occur. Linear-leaved species have few flavonoids and their biochemical profiles resemble those of submersed leaves of heterophyllous species. Broad-leaved homophyllous species possess flavonoid profiles more similar to those of the floating leaves of heterophyllous species. Numerical analysis of these chemical data is consistent with phylogenetic relationships within the genus derived independently on the basis of morphological and chromosomal data. Glycoflavones, which are probably maintained in floating leaves because of their UV filtering ability, exhibit the most pronounced biochemical heterophylly in Potamogeton. The lack of glycoflavones in submersed leaves of heterophyllous species and in linear-leaved homophyllous species is attributable to the ability of naturally colored water to significantly absorb harmful UV radiation. These observations provide strong support for earlier hypotheses suggesting the importance of flavonoid evolution in the conquest of exposed terrestrial habitats by plants.     

Difference in cuticular transpiration and sclerophylly in juvenile and adult pine needles relates to the species-specific rates of development

Pinus species show remarkable ontogenetic differences in needle morphology (heterophylly) between juvenile and adult vegetative phases. This developmental shift may play an adaptative role in their success under diverse habitats. As a first step to know the functional differences between each vegetative phase, we compared water loss through the cuticles of juvenile and adult needles of 21-month-old nursery-grown seedlings of nine hard pine species. Cuticular transpiration (CT), calculated after complete stomatal closure, was obtained by leaf-drying curves, and was related to leaf, ontogenetic and climatic parameters. The rate of cuticular transpiration (RCT) between juvenile and adult needles differed across pine species, and in particular segregated the Mediterranean species Pinus canariensis and P. halepensis, from the Eurasian P. uncinata and introduced species P. radiata. For these species, RCT was always higher in juvenile needles. The different leaf and ontogenic parameters studied were correlated with the variation in RCT among the nine pine species. We discuss this relationship in the light of the species ecology. Besides their possible adaptive interpretation, these results suggest an underlying need to consider the ontogenetic heterophylly when assessing functional traits in hard pine seedlings, in particular those traits that govern water relations.     

Using DNA‐based techniques to identify hybrids among linear‐leaved Potamogeton plants collected in China

Abstract It is well known that interspecific hybrids occur in the genus Potamogeton. The linear‐leaved Potamogeton species commonly have highly variable morphological characteristics. Their hybrids often show similar vegetative characters to their parental species and their identification based solely on morphology is not always conclusive. In order to clarify whether there are any hybrids from the linear‐leaved Potamogeton plants collected in China, we used internal transcribed spacers (ITS) of nuclear ribosomal DNA and chloroplast rbcL gene sequences to identify the hybrids. Using ITS sequence additivity, we identified four hybrids, namely P. orientalis (P. pusillus×P. oxyphyllus), P. pusillus×P. berchtoldii, P. foliosus×P. octandrus, and P. cristatus×P. octandrus. The latter three hybrids should be considered as new hybrids in Potamogeton. The maternal parents of the four hybrids were confirmed using chloroplast rbcL gene sequences.     

水体溶氧影响陆生植物喜旱莲子草(Alternanthera philoxeroides)和牛鞭草(Hemarthria altissima)对完全水淹的耐受力

溶氧是水环境中一个重要的环境因子,为了探讨水中的溶氧含量水平是否会对陆生植物的耐淹能力造成影响,研究了陆生植物喜旱莲子草(Alternanthera philoxeroides)和牛鞭草(Hemarthria altissima)在遭受不同溶氧含量水体完全淹没后的生长表现、存活情况和非结构碳水化合物的变化。实验结果表明:(1)水体中的溶氧含量显著影响了处于完全水淹环境中的喜旱莲子草和牛鞭草的存活。受高溶氧水体完全水淹的喜旱莲子草和牛鞭草主茎的完好程度和存活叶的数量均显著高于遭受低溶氧水体完全水淹的喜旱莲子草和牛鞭草,喜旱莲子草和牛鞭草在高溶氧水体完全水淹后的生物量比低溶氧水体完全水淹后要高;(2)水体中的溶氧含量显著影响了处于完全水淹环境中的喜旱莲子草和牛鞭草的生长,受高溶氧水体完全水淹的喜旱莲子草主茎伸长生长和不定根生长显著强于受低溶氧水体完全水淹的喜旱莲子草,在不定根的生长上牛鞭草也具有同样的表现。(3)高溶氧水环境有利于减小被完全淹没的喜旱莲子草和牛鞭草的碳水化合物消耗,两种植物在受高溶氧完全水淹后体内具有的非结构性碳水化合物含量均比受低溶氧完全水淹后高。(4)喜旱莲子草比牛鞭草能更好地耐受完全水淹,当处于低溶氧完全水淹时表现得更为明显,本研究表明入侵物种喜旱莲子草比本地物种牛鞭草具有更强的环境适应能力和水淹耐受能力。     

Exposure to water increased pollen longevity of pondweed (Potamogeton spp.) indicates different mechanisms ensuring pollination success of angiosperms in aquatic habitat

Pollen longevity in seven Potamogeton species representing different pollination systems (anemophily, epihydrophily and hydroautogamy) was assessed both under aerial condition and in contact with water to investigate how water impacts the sexual reproduction in these aquatic taxa. Stainability of pollen with MTT was considered as an indicator of pollen viability. The half-life of pollen longevity was calculated using exponential decay regression. Overall, pollen viability decreased relatively rapidly with time. Pollen grains of obligate anemophilic species had lower initial viability and shorter half-lives than those of facultative anemophilic species. Pollen in these latter species may take more time to reach the stigma. The pollen of Potamogeton may be categorized as partially hydrated pollen owing to its generally spherical shape and lack of furrows, rapid loss of viability, and fast pollen tube initiation. The half-life is positively correlated with pollen size. Smaller-sized grains are at greater risk of desiccation than larger grains. In contrast with the situation observed in most terrestrial angiosperms, contact with water increases pollen longevity in Potamogeton species. In our present study the half-lives of pollen longevity of Potamogeton species in which the pollen had come into contact with water (mean of 10.65 h) were markedly higher than those under aerial conditions (mean of 5.79 h, t = 2.622, P = 0.039). The results of our study contradict a widely held belief that water is detrimental to pollen viability in angiosperms and furthermore indicate that close proximity to water results in selection for wettability. The transition to a hydrated status together with its morphology, make Potamogeton pollen more adapted to the aquatic environment and thus serves to ensure reproductive process. Results of our present study may have direct implications for understanding the evolution of the sexual reproductive system in aquatic angiosperms.     

Macrobenthos of a tidal impoundment at the Mai Po Marshes Nature Reserve,Hong Kong

The composition and spatial distribution patterns of the macrobenthic faunal assemblages of an 8-ha tidal impoundment operated as a traditional shrimp pond at the Mai Po Marshes Nature Reserve, Hong Kong, were studied in relation to temporal changes in local environmental conditions. Species richness, abundance and biomass of macrobenthos across 5 different sub-habitats (seaward, middle, and landward parts of open water unvegetated areas, and Phragmites- and Kandelia-dominated, vegetated areas) within the pond were examined bimonthly between January 1997 and January 1998. Grab samples were collected randomly within the sub-habitats. Key physical environmental parameters of the sampling sites were also measured. A total of 46 species of macrobenthos was recorded: 11 polychaetes, 11 molluscs, 13 crustaceans and 11 insects. Mean species density in the five sub-habitats ranged from 0 to 3907 indm^–2, with mean biomass ranging from 0 to 96.9 gm^–2. The macrobenthos showed spatial and temporal differences among the sub-habitats and across sampling times. Species abundances of Polychaeta, Mollusca and Crustacea were significantly higher in the three open water areas than in the two vegetated (Phragmites- and Kandelia-dominated) areas, with an inverse pattern for Insecta. There were no clear temporal patterns although abundance and biomass generally increased in the cooler months. Results of a canonical correspondence analysis suggest that macrobenthic species richness, abundance and biomass in the open areas were positively correlated with salinity, while water depth, dissolved oxygen and sediment organic matter content had little relationship with the macrobenthic assemblage parameters. Ordination by multi-dimensional scaling suggests that different habitats supported distinct macrobenthic assemblages. The macrobenthic assemblage in the tidal pond was less species rich but denser than those in the neighboring tidal mangrove and mudflat, suggesting that conversion of these areas into extensively managed tidal aquaculture ponds results in reduced species richness in tropical mangrove habitats.     

Habitat characteristics of an alien species <Emphasis Type="Italic">Elodea canadensis</Emphasis> in Slovenian watercourses

The distribution, abundance and habitat characteristics of an alien species, Elodea canadensis, were surveyed in watercourses in Slovenia. The accompanying plant community was also examined. Distribution and abundance of macrophytes were assessed in reaches of different length, and habitat assessment is based on 12 parameters of the Riparian, Channel, and Environmental (RCE) Inventory. E. canadensis thrived in 132 out of 1,227 reaches examined and in 12 of the 39 watercourses surveyed. It grew in the company of a variety of species, most frequently with different species of Potamogeton. It was rarely found as the prevailing, and never as the only species in any reach. Canonical correspondence analysis (CCA) of reaches with E. canadensis revealed that the presence of detritus, retention structures and properties of the riparian zone explained most of the variance in community composition. Habitat analysis of well-established stands of E. canadensis showed that its preferred habitats were watercourses flowing through agricultural landscape, with a narrow, more or less disturbed riparian zone, with moderate presence of retention structures, and with sediment that was a mixture of gravel, sand and silt with either coarse or fine organic matter. It was not found in the parts of streams with the most dynamic flow, and was absent from watercourses in the karst region, due to the frequent and extreme water level fluctuations. The alien species E. canadensis did not express its invasive character in heterogeneous watercourses with rich macrophyte communities.     

An invasive macrophyte alters sediment chemistry due to suppression of a native isoetid

The submersed macrophyte Utricularia inflata (inflated bladderwort) is a recent invader of Adirondack Mountain lakes (NY, USA). A 15-week greenhouse experiment and a 7-week field experiment were conducted to test the hypothesis that this rootless species fundamentally changes sediment chemistry through its suppression of the native short-statured species, Eriocaulon aquaticum. E. aquaticum has an extensive root system that releases oxygen into the sediment. In greenhouse conditions, E. aquaticum raised the porewater redox potential of otherwise bare sediment from 25 to 324 mV, lowered the sediment porewater pH from 5.7 to 4.6, and depleted the dissolved inorganic carbon and ammonium concentrations in the sediment porewater by 68.4 and 96.0%, respectively (P<0.001 for all four parameters). A cover of U. inflata over E. aquaticum, however, greatly reduced the latter’s effect on redox potential (P<0.001), dissolved solutes (P<0.001), and pH (P<0.05). E. aquaticum biomass increased during the greenhouse experiment in the absence of U. inflata, but decreased in its presence (P<0.001). Redox and growth rate results from the field experiment paralleled those from the greenhouse experiment. Our data suggest that U. inflata may change nutrient cycling in Adirondack lake ecosystems by reducing the growth of native isoetid macrophytes, such as E. aquaticum, and consequently altering key features of sediment chemistry.