Allelopathic effect of Nymphaea lotus L. on growth and yield of cultivated rice around Lake Manzala (Nile Delta)

Lotus infestation of ricefields is a major cause of crop failure and decrease of grain yield in the newly reclaimed cut-off areas around lake Manzala, Egypt. This study provides insights in the allelopathic effect of Nymphaea lotus L. on rice (Oryza sativa cavr. Giza-177). Lotus rhizome extracts were inhibitory to seed germination and seedling growth of rice. The degree of inhibition was dependent on extract type and concentration. Ethanol and water extracts were more inhibitory than chloroform extracts. The phenolic fraction of ethanol extracts showed the highest inhibitory effects. In a target (rice)-neighbour (lotus) pot experiment, rice dry mass and relative growth rate were dependent on its age and on lotus rhizome density, with decreased growth at increased lotus density. Field data on infested and non-infested ricefields demonstrated a decreased leaf area index and yield in infested fields. Identification of the potential allelochemical compounds by gas chromatography/mass spectrometry revealed the presence of allelopathic phenolics in lotus rhizomes.     

Habitat preferences of Eurasian Bitterns Botaurus stellaris booming in ricefields: implications for management

The Eurasian Bittern Botaurus stellaris suffered declines in western Europe during the 20th century, partly because of wetland reclamation. The species has been traditionally considered a reedbed specialist but recent studies identified a greater ecological plasticity than previously believed. We investigated habitat associations of a Eurasian Bittern population that has started to breed in the ricefields of northwest Italy since the early 1990s. Booming Bitterns had a higher probability of occurring in ricefields with taller rice plants, more vegetated field banks, more weeds, a larger surface and closer to remaining natural wetlands. The positive effect of field bank vegetation height on the probability that a ricefield hosted a booming Bittern declined late in the season, in contrast to the effects of weeds and ricefield area, which were stronger later in the season. A decreasing importance of vegetation on field banks to booming Bitterns may be a consequence of seasonal changes in habitat structure through the Bittern’s breeding period. The degree of flooding did not affect the probability of occurrence of booming Bitterns, probably because most ricefields were homogeneously flooded during the peak breeding season (June–July). Our findings have important implications for the management of Bittern populations breeding in the ricefields of northwest Italy. We propose simple conservation actions that may favour the occurrence of booming Bitterns and help the species spread in this novel habitat.     

The influence of water level and salinity on plant assemblages of a seasonally flooded Mediterranean wetland

We studied the key environmental variables shaping plant assemblages in Mediterranean abandoned ricefields with contrasting freshwater inputs over saline sediments. Plant species cover, water levels and soil variables were studied following a stratified random sampling design. Multivariate analysis identified water regime, particularly summer and autumn irrigation, as the most important environmental variable associated with vegetation composition. Distribution of annual and emergent macrophytes was not associated to salinity as found at the study site (0.57–4.1 mS/cm). Increased soil salinity, caused by summer irrigation near the soil surface did affect shallow-marsh assemblage distribution. These key environmental characteristics allowed us to identify six main assemblages. Annual macrophytes (such as Zannichellia palustris) were defined by high (over 10 cm) annual mean water level (MWL) and early successional conditions; emergent macrophytes (such as Typha spp., Scirpus lacustris) by annual MWL of 10 to − 25 cm and continuous shallow flooding in summer and autumn (MWL of 0–10 cm). The shallow-marsh group, correlated with annual MWL − 25 to − 100 cm, separated into two subgroups by salinity: grassland (including Paspalum distichum) with summer and autumn MWL below − 25 cm and brackish (with Juncus subulatus or Agrostis stolonifera) with summer and autumn MWL just below the soil surface (0 to − 25 cm). Water levels for the grassland subgroup may equate with a salinity ‘refuge’ for P. distichum. Time was a further determinant of variation in the full data set. Abundance of a large group of agricultural annuals (such as Sonchus tenerrimus) and damp ground annuals (including ricefield weeds such as Ammania robusta) decreased with time as bare ground disappeared. Maintenance of spatial vegetation heterogeneity in abandoned ricefields is contingent on continued water regime management.     

Application of Arabidopsis AGAMOUS second intron for the engineered ablation of flower development in transgenic tobacco

To explore a new approach to generating reproductive sterility in transgenic plants, the barnase gene from Bacillus amyloliquefaciens was placed under the control of an 1853-bp nucleotide sequence from the 3′end of the second intron of Arabidopsis AGAMOUS and CaMV 35S (−60) minimal promoter [AG-I-35S (−60)::Barnase], and was introduced into tobacco through transformation mediated by Agrobacterium tumefaciens. All AG-I-35S (−60)::Barnase transgenic plants showed normal vegetative growth and 28% of the transgenic lines displayed complete ablation of flowering. Two transgenic lines, Bar-5 and Bar-15, were 98.1 and 98.4% sterile, respectively, as determined by seed production and germination. When controlled by AG-I-35S (−60) chimeric promoter, barnase mRNA was detected in the reproductive tissues of transgenic tobacco plants, but not in vegetative parts. This study presents the first application of an AG intron sequence in the engineered ablation of sexual reproduction in plants. The AG-I-35S (−60)::Barnase construct can be useful in diminishing pollen and seed formation in plants, providing a novel bisexual sterility strategy for interception of transgene escape and has other potentially commercial use for transgenic engineering.     

The dynamics of seed harvesting in early successional communities by a tropical ant,Solenopsis geminata

Summary The neotropical ant, Solenopsis geminata, in the moist lowlands of southeastern Mexico was most abundant in agricultural fields and early second growth habitats. It was not found within forest habitats.In addition to its foraging for insects and general scavenging, this ant also harvests seeds. Under field experimental conditions, a wide variety of small seeds, especially grasses, were taken. Nest mound size and number were greatest on plots experimentally seeded to high grass density and low on plots consisting of grass-dicot mixtures, pure dicot stands, or a vegetative grass strain incapable of seed production. Paspalum conjugatum, an important grass weed, was the most common seed encountered in seed storage chambers in the mounds. Under experimental field conditions, Solenopsis geminata reduced seed densities of P. conjugatum and the malvaceous weed, Malachra sp. by 97 percent or more. Seed densities of the composite, Bidens pilosa were unaffected.     

Nitrogen Relationships of Vigna mungo in Pure Stands and in Celosia argentea Mixtures

Dynamics of the nitrogen relationships of Vigna mungo in pureand in mixed stands with Celosia argentea, a common weed ofleguminous crops in certain regions of India, were investigated.The weed significantly depressed nodulation and reduced thedry matter and nitrogen yield of the legume which was lowestat the highest density of the weed. A significant amount ofnitrogen transfer occurred from the legume in the weed mixtureswhich appeared to be taken up by the weed plants. Therefore,weed plants benefited from their association with the legumeby accumulating more dry matter and nitrogen in the legume mixtures.The possible competitive or biochemical interference of theweed with nitrogen relationships of the legume in mixtures isdiscussed. Vigna mungo, Celosia argentea, pure stands, mixed stands, total nitrogen, interference     

两种生境中薇甘菊种群的生物量生殖分配

于2004年薇甘菊（Mikania micrantha）生殖阶段的现蕾期至种子成熟期,从种群和构件水平上研究了两种生境（林窗和开阔地）中薇甘菊种群的生物量生殖分配。结果表明,在生殖生长过程中,两种生境中的种群用于营养生长的生物量分配均占有绝对优势,而生殖生长的波动相对较大。花序的生物量分配（RA）总体上均呈现由低到高的变化趋势。在不同时期,林窗薇甘菊种群的营养枝生物量分配均小于开阔地,而除了种子形成期和种子成熟期以外的其它各个时期,林窗中生殖枝的生物量分配均大于开阔地,林窗中花序的生物量分配均显著大于开阔地。表明薇甘菊能有效权衡其在不同生境中的繁殖策略,开阔地中的薇甘菊种群的繁殖策略倾向于克隆繁殖,而林窗生境中薇甘菊种群则相对更倾向于有性生殖。     

CO2 enrichment reduces reproductive dominance in competing stands of Ambrosia artemisiifolia (common ragweed)

Plants growing in dense stands may not equally acquire or utilize extra carbon gained in elevated CO₂. As a result, reproductive differences between dominant and subordinate plants may be altered under rising CO₂ conditions. We hypothesized that elevated CO₂ would enhance the reproductive allocation of shaded, subordinate Ambrosia artemisiifolia L. (Asteraceae) individuals more than that of light-saturated dominants. We grew stands of A. artemisiifolia at either 360 or 720 μL L⁻¹ CO₂ levels and measured the growth and reproductive responses of competing individuals. To test whether elevated CO₂ altered size and reproductive inequalities within stands, we compared stand-level coefficients of variation (CV) in height growth and final shoot, root, and reproductive organ biomasses. Elevated CO₂ enhanced biomass and reduced the CV for all aspects of plant growth, especially reproductive biomass. Allocation to reproduction was higher in the elevated CO₂ than in the ambient treatment, and this difference was more pronounced in small, rather than large plant positive relationships between the CV and total stand productivity declined under elevated CO₂, indicating that growth enhancements to smaller plants diminished the relative biomass advantages of larger plants in increasingly crowded conditions. We conclude that elevated CO₂ stimulates stand-level reproduction while CO₂-induced growth gains of subordinate A. artemisiifolia plants minimize differences in the reproductive output of small and large plants. Thus, more individuals are likely to produce greater amounts of seeds and pollen in future populations of this allergenic weed.     

Temporal and structural effects of stands on litter production in Melaleuca quinquenervia dominated wetlands of south Florida

Melaleuca quinquenervia dominates large areas of the Florida Everglades in the southeastern USA where it has transformed sedge-dominated marshes into melaleuca forests. Despite its prevalence, very little is known about the ecology and stand dynamics of this invasive tree. We delineated large-, intermediate-, and small-tree stands in non-flooded, seasonally flooded and permanently flooded areas of Florida in 1997, measured their biological attributes, and then quantified litterfall components for 3–4 year periods. Melaleuca wood components and mature seed-capsules comprised the largest and the smallest portions of aboveground biomass, respectively, while leaves, fine stems, mature fruits, bud scales, floral structures, and residues represented decreasingly smaller fractions of the litter during the succeeding year. Dry weight proportion of leaves in litter was greatest (80.9%) in non-flooded and least (69.1%) in permanently flooded habitats. It was also greatest in small (85.6%) and least in large (64.7%) tree stands. Reproductive structures and mature-fruit fractions in litter were highest in large-tree stands whereas the bud-scale fraction showed no relationship to tree size. Seasonally flooded habitats had the most litterfall, wherein small-, intermediate-, and large-tree stands generated 0.662, 0.882, and 1.128 kg m⁻² yr⁻¹, respectively. Dry weight of stems, leaves, bud–scales, floral structures, and mature fruit fractions in litter increased as the predominant size of the trees in the stand increased. Total annual litter production was highest during 1999–2000. Leaf fall occurred year-round with maximal amount during April, July, and October. Highest amounts of bud scales and floral structures fell during October–January, which corresponded with flushes of vegetative growth and major flowering events. Overall, melaleuca alone accounted for nearly 99% of the total litterfall dry weight in all habitats and months sampled. The amount of non-melaleuca litter was greater in small-tree stands than in intermediate- or large-tree stands. Litterfall data of this nature will be helpful in detecting changes occurring in melaleuca canopies in response to biological control impact and in prescribing site-specific management strategies.     

Asexual Endophytes in a Native Grass: Tradeoffs in Mortality, Growth, Reproduction, and Alkaloid Production

Neotyphodium endophytes are asexual, seed-borne fungal symbionts that are thought to interact mutualistically with their grass hosts. Benefits include increased growth, reproduction, and resistance to herbivores via endophytic alkaloids. Although these benefits are well established in infected introduced, agronomic grasses, little is known about the cost and benefits of endophyte infection in native grass populations. These populations exist as mosaics of uninfected and infected plants, with the latter often comprised of plants that vary widely in alkaloid content. We tested the costs and benefits of endophyte infections with varying alkaloids in the native grass Achnatherum robustum (sleepygrass). We conducted a 4-year field experiment, where herbivory and water availability were controlled and survival, growth, and reproduction of three maternal plant genotypes [uninfected plants (E−), infected plants with high levels of ergot alkaloids (E+A+), and infected plants with no alkaloids (E+A−)] were monitored over three growing seasons. Generally, E+A+ plants had reduced growth over the three growing seasons and lower seed production than E− or E+A− plants, suggesting a cost of alkaloid production. The reduction in vegetative biomass in E+A+ plants was most pronounced under supplemented water, contrary to the prediction that additional resources would offset the cost of alkaloid production. Also, E+A+ plants showed no advantage in growth, seed production, or reproductive effort under full herbivory relative to E− or E+A− grasses, contrary to the predictions of the defensive mutualism hypothesis. However, E+A+ plants had higher overwintering survival than E+A− plants in early plant ontogeny, suggesting that alkaloids associated with infection may protect against below ground herbivory or harsh winter conditions. Our results suggest that the mosaic of E−, E+A+, and E+A− plants observed in nature may result from varying biotic and abiotic selective factors that maintain the presence of uninfected plants and infected plants that vary in alkaloid production.     

Seasonal variation in the phytomass,chemical composition and nutritional value of Azolla filiculoides Lam. along the water courses in the Nile Delta,Egypt

The present study aims to assess phenological behaviour, phytomass production, chemical composition and nutritional value of Azolla filiculoides in the water courses of the Nile Delta, Egypt. The sampling process was carried out seasonally using twenty‐five plots (each of 1 × 1 m) distributed along 15 irrigation canals and 10 drainage canals in the study area. Sprouting of A. filiculoides had its maximum activity during winter, vegetative growth during spring and summer and withering during autumn. Maximum seasonal phytomass (285.2 g DW m^‐2) was found during spring. The annual mean was significantly higher in drainage canals (278.3 g DW m^‐2) than in irrigation canals (144.4 g DW m^‐2). The concentrations of Ca, Mg and Na in A. filiculoides from drainage canals were significantly higher than in those from irrigation canals. Regarding the type of water courses, there were no significant differences in organic contents and nutritive values between the irrigation and drainage canals. The analysis of growth characteristics indicated that A. filiculoides can grow quite well in drainage canals; its macronutrient (N, Ca, Mg, Na and Fe) contents are high enough to allow it to be used as a bio‐fertilizer. On the other hand, A. filiculoides could be considered as a ‘nutrients and heavy metals remover’ especially in drainage canals for wastewater treatment if the plant is harvested during its maximum phytomass. As feed supplement for animals, this plant could be considered as excellent forage because its high levels of carbohydrate, protein, crude fat, total digestible nutrients and the lower crude fiber contents (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phenology of Chondrus ocellatus in Cheongsapo Near Busan, Korea

The reproductive phenology of Chondrus ocellatus and the effects of temperature and light on its growth were examined in Cheongsapo near Busan, Korea, from September 1994 to August 1995. The vegetative plants dominated over the year, with a peak occurrence in January. Gameto- and tetrasporophytes were most abundant in November and August. All vegetative and reproductive plants had a peak both in length and weight in October, when seawater temperature was highest (24°C). In laboratory culture, the maximum relative growth rate (RGR) of 2.94% day⁻¹ was obtained at 20°C and 100 μmol photons m⁻² s⁻¹, whereas the lowest value was recorded at 25°C and 100 μmol photons m⁻² s⁻¹ in a 12: 12 h LD photoperiod regime. Among the three photoperiod regimes (8:16 h, 12:12 h, 16:8 h LD) tested, there was evidence of a higher RGR in the 12:12 h LD cycle. This result suggests that the growth and reproduction of C. ocellatus are correlated with the seawater temperature based on laboratory culture and field observations.     

Clonal integration supports the expansion from terrestrial to aquatic environments of the amphibious stoloniferous herb Alternanthera philoxeroides

Effects of clonal integration on land plants have been extensively studied, but little is known about the role in amphibious plants that expand from terrestrial to aquatic conditions. We simulated expansion from terrestrial to aquatic habitats in the amphibious stoloniferous alien invasive alligator weed ( Alternanthera philoxeroides ) by growing basal ramets of clonal fragments in soils connected (allowing integration) or disconnected (preventing integration) to the apical ramets of the same fragments submerged in water to a depth of 0, 5, 10 or 15 cm. Clonal integration significantly increased growth and clonal reproduction of the apical ramets, but decreased both of these characteristics in basal ramets. Consequently, integration did not affect the performance of whole clonal fragments. We propose that alligator weed possesses a double-edged mechanism during population expansion: apical ramets in aquatic habitats can increase growth through connected basal parts in terrestrial habitats; however, once stolon connections with apical ramets are lost by external disturbance, the basal ramets in terrestrial habitats increase stolon and ramet production for rapid spreading. This may contribute greatly to the invasiveness of alligator weed and also make it very adaptable to habitats with heavy disturbance and/or highly heterogeneous resource supply.     

Effects of resource availability on the trade-off between seed and vegetative reproduction

Aims To explore whether the trade-off between seed and vegetative reproductive modes is flexible in environments with different amounts of available resources to maintain optimal behaviors.Methods A transition matrix model was established to determine the optimal trade-off between seed and vegetative reproduction in resources–variable habitats.Important findings The model predicts that plants allocate more resources to seed reproduction when available resources are scarce. With increasing resources, more vegetative propagules are produced. However, if resources keep increasing to a harmful level, plants would switch to seeds again.     

Phenotypic plasticity rather than locally adapted ecotypes allows the invasive alligator weed to colonize a wide range of habitats

Both phenotypic plasticity and locally adapted ecotypes may contribute to the success of invasive species in a wide range of habitats. Here, we conducted common garden experiments and molecular marker analysis to test the two alternative hypotheses in invasive alligator weed (Alternanthera philoxeroides), which colonizes both aquatic and terrestrial habitats. Ninety individuals from three pairs of aquatic versus terrestrial populations across southern China were analyzed, using inter simple sequence repeat (ISSR) marker, to examine population differentiation in neutral loci. Two common gardens simulating aquatic and terrestrial habitats were set up to examine population differentiation in quantitative traits. We found no evidence of population differentiation in both neutral loci and quantitative traits. Most individuals shared the same ISSR genotype. Meanwhile, plants from different habitats showed similar reaction norms across the two common gardens. In particular, plants allocated much more biomass to the belowground roots in the terrestrial environment, where alligator weed may lose part or all of the aboveground shoots because of periodical or accidental disturbances, than those in the aquatic environment. The combined evidence from molecular marker analysis and common garden experiments support the plasticity hypothesis rather than the ecotype hypothesis in explaining the adaptation of alligator weed in a wide range of habitats.     

Morphological analysis of alpine communities of the north-western Caucasus

The species composition of four alpine communities in the north-western Caucasus was subjected to a morphological analysis. The communities are an alpine lichen heath type (ALH), aFestuca varia grassland type (FVG), aGeranium-Hedysarum meadow type (GHM) and a snowbed community (SBC). Eighty-two species were studied, using the following morphological parameters: vegetative mobility, presence of rosettes, architectural model, life form according toRaunkiaer and life form according toSerebryakov. Representation spectra were calculated on the basis of species presence, above-ground phytomass proportion and species frequency. The results show that most alpine species have a low vegetative mobility; a semi-rosette growth form; a sympodial semi-rosette model of shoot formation and that they are characterised by the prevalence of hemicryptophytes. Differences between the four communities were found in the following features: tap-rooted and short-rhizome plants dominate in ALH and, moreover, dense-tussock plants are dominant in the phytomass; short-rhizome (species presence) and dense- tussock plants (phytomass) are dominant in FVG; short-rhizome and loose-tussock plants dominant in GHM; semi-shrub (phytomass basis) and loose-tussock plants are dominant of SBC. Tuberiferous, bulbiferous and monocarpic plants are not important in any of the communities. *** DIRECT SUPPORT *** A02DO006 00008     

The productive and reproductive biology of flowering plants

The life cycles, programme of energy expenditure and allocation to reproduction, and the reproductive efforts of three wildAllium species, i.e.,A. Victorialis ssp.platyphyllum, A. monanthum, andA. Grayi, all native to Japan, were studied and compared. Furthermore, their adaptive strategies were discussed from the point of view of life history strategy. First, the reproductive systems, number of male and female gametes borne, and the number and size of propagules produced were critically investigated. In order to estimate the crude reproductive efficiency (sensu Harper and Ogden, 1970) of these species, sequential harvests were taken and the plants were divided into their component structures, dried and weighed. The quantity of dry weight allocated to sexual or vegetative reproduction was obtained by weighing the seeds, bulbils, or bulblets produced at the end of the season. A. Victorialis ssp.platyphyllum showed a rather low reproductive effort. However, the mean seed output per plant was 34.8±16.8 and the productivity appeared very constant every season. Thus, in the natural populations young plants are borne and recruited every season by means of sexual reproduction. A. monanthum was found to be characterized by annual type dry matter economy. The sexuality and reproductive systems of this species turned out to be extremely complex, and ten different reproductive types were distinguished. The exceedingly low efficiency of sexual reproduction in this species is apparently supplemented by vegetative propagation. The dry matter allocation to daughter bulbs at final harvest was very high; whereas the allocation to sexual reproduction was extremely low. InA. Grayi (a polyploid complex of 4X, 5X, and 6X), a surprisingly high amount of the total annual net assimilate is allocated to the bulbils and bulblets. On the other hand, sexual reproductive effort in this species is exceedingly low, even in obligate amphimictic plants. Thus, the recruitment of individuals in a population of this species appears to be largely dependent on vegetative reproduction. Considering the number of bulbils produced in the scape heads, their dispersibility, germinability, and rapid growth after sprouting, the bulbils evidently possess a function almost comparable to seeds. This species no doubt possesses an adapative strategy to unstable, open habitats exposed to frequent disturbances. It is concluded that the life history strategies of plants, as characterized here in this paper for three wildAllium species, have doubtlessly differentiated by adapting to the respective ecological backgrounds of their habitats.     

The evolution of competitive strategies in annual plants

Annual plants are common in disturbed habitats. It is frequently assumed that because these habitats often have low-plant density, competition is not important in shaping the ecological strategies of annual plants. We test for competitive strategies in genotypes of the short-lived annual plant Arabidopsis thaliana. Genotypes were grown in treatments with or without conspecific competitors. We measured size at reproduction and fitness (fruit production) at final development. We estimated competitive ability in each genotype at first reproduction (the ability to maintain size in the presence of competitors) and at final development (the ability to maintain fruit production in the presence of competitors). Genotypes showed relatively high competitive ability measured as fruit production at final development, but most genotypes had low competitive ability measured as size at reproduction. Our results suggest that competition has been important in the evolution of strategies in these genotypes but vegetative size is not a strong predictor of competitive ability. Rather, competitive ability is determined by the capacity to reproduce efficiently in the presence of competitors. The competitive strategies expressed across these genotypes suggest that competition has been a selective force in these plants, and that a fast life history is not equivalent to an “r-strategy.”     

Post-logging organic matter recovery in forest ecosystems of eastern Baikal region

The dynamics of organic matter accumulated in the soil and main vegetation elements was analyzed for post-logging forest ecosystem succession series in eastern Baikal region. The phytomass was found to allocate up 63 and 50% of carbon in undisturbed Scots pine and fir stands, respectively. The post-logging phytomass contribution to the total carbon pool appeared to decrease down to 16% in Scots pine and 6% in fir stands. In Scots pine stands, carbon storage was determined to account for almost 70% of the initial carbon 60 years after logging. In 50- to 55-year-old fir stands, carbon recovered its initial pool only by 10%. Soil carbon recorded in recently logged Scots pine and fir sites appeared to be 5 and 16 times that accumulated in the phytomass, respectively. The ratio between phytomass carbon and soil organic matter recovered back to the prelogging level in Scots pine stands by the age of 50–60 years. While phytomass carbon also increased in fir stand of the same age, it did not reach the level of the control stand.     

Spatial and seasonal patterns of periphyton biomass and productivity in the northern Everglades,Florida, U.S.A.

We sampled periphyton in dominant habitats at oligotrophic and eutrophic sites in the northern Everglades during the wet and the dryseasons to determine the effects of nutrient enrichment on periphytonbiomass, taxonomic composition, productivity, and phosphorus storage. Arealbiomass was high (100–1600 g ash-free dry mass [AFDM]m⁻²) in oligotrophic sloughs and in stands of the emergentmacrophyte Eleocharis cellulosa, but was low in adjacent stands of sawgrass,Cladium jamaicense (7–52 g AFDM m⁻²). Epipelon biomasswas high throughout the year at oligotrophic sites whereas epiphyton andmetaphyton biomass varied seasonally and peaked during the wet season.Periphyton biomass was low (3–68 g AFDM m⁻²) and limitedto epiphyton and metaphyton in open-water habitats at eutrophic sites andwas undetectable in cattail stands (Typha domingensis) that covered morethan 90% of the marsh in these areas. Oligotrophic periphytonassemblages exhibited strong seasonal shifts in species composition and weredominated by cyanobacteria (e.g., Chroococcus turgidus, Scytonema hofmannii)during the wet season and diatoms (e.g. Amphora lineolata, Mastogloiasmithii) during the dry season. Eutrophic assemblages were dominated byCyanobacteria (e.g., Oscillatoria princeps) and green algae (e.g., Spirogyraspp.) and exhibited comparatively little seasonality. Biomass-specific grossprimary productivity (GPP) of periphyton assemblages in eutrophic openwaters was higher than for comparable slough assemblages, but areal GPP wassimilar in these eutrophic (0.9–9.1 g C m⁻²d⁻¹) and oligotrophic (1.75–11.49 g C m⁻²d⁻¹) habitats. On a habitat-weighted basis, areal periphytonGPP was 6- to 30-fold lower in eutrophic areas of the marsh due to extensiveTypha stands that were devoid of periphyton. Periphyton at eutrophic siteshad higher P content and uptake rates than the oligotrophic assemblage, butstored only 5% as much P because of the lower areal biomass.Eutrophication in the Everglades has resulted in a decrease in periphytonbiomass and its contribution to marsh primary productivity. These changesmay have important implications for efforts to manage this wetland in asustainable manner. This revised version was published online in July 2006 with corrections to the Cover Date.