Seasonal variation in seed bank composition and its interaction with nutrient enrichment in the Everglades wetlands

In the Florida Everglades, nutrient enrichment from agricultural outflow and the change in hydrology have collectively contributed to the expansion of cattails (Typha spp.). To assess the effectiveness of prescribed fire in controlling cattails and to predict vegetation dynamics after the fire, it is important to understand the seasonal variation of the soil seed bank and how the seed bank is affected by nutrient enrichment and fire. This paper investigates the effects of season, nutrient enrichment, and fire on soil seed bank species composition, richness, and density along a nutrient gradient in Water Conservation Area 2A (WCA 2A) of the Florida Everglades. Species richness was significantly affected by nutrient enrichment and season but not their interaction. Total seed density, however, was significantly affected by the interaction between nutrient enrichment and season. Yet, at species level, the relationship between seed density, nutrient enrichment and season varied. The highest seed density of cattail occurred in summer at highly enriched sites, but that of sawgrass occurred in fall regardless of enrichment; the seed density of water lily was very low regardless of season and nutrient enrichment, and the highest Amarathus seed density occurred at highly enriched sites year round. Moreover, germination timing differed greatly among species. While cattail seeds had a short incubation period and started to germinate 2–3 days after initiation of the germination assay, sawgrass seeds generally started to germinate 4 weeks later. Further, both the prescribed summer fire at the highly enriched site and the natural winter fire at the moderately enriched site reduced the seed density of cattail but not of sawgrass. Our results suggest that fire application for vegetation recovery in WCA 2A would benefit from explicitly considering seasonal dynamics of the seed bank.     

Freshwater wetlands: fertile grounds for the invasive Phragmites australis in a climate change context

Climate change will likely affect flooding regimes, which have a large influence on the functioning of freshwater riparian wetlands. Low water levels predicted for several fluvial systems make wetlands especially vulnerable to the spread of invaders, such as the common reed (Phragmites australis), one of the most invasive species in North America. We developed a model to map the distribution of potential germination grounds of the common reed in freshwater wetlands of the St. Lawrence River (Québec, Canada) under current climate conditions and used this model to predict their future distribution under two climate change scenarios simulated for 2050. We gathered historical and recent (remote sensing) data on the distribution of common reed stands for model calibration and validation purposes, then determined the parameters controlling the species establishment by seed. A two‐dimensional model and the identified parameters were used to simulate the current (2010) and future (2050) distribution of germination grounds. Common reed stands are not widespread along the St. Lawrence River (212 ha), but our model suggests that current climate conditions are already conducive to considerable further expansion (>16,000 ha). Climate change may also exacerbate the expansion, particularly if river water levels drop, which will expose large bare areas propitious to seed germination. This phenomenon may be particularly important in one sector of the river, where existing common reed stands could increase their areas by a factor of 100, potentially creating the most extensive reedbed complex in North America. After colonizing salt and brackishwater marshes, the common reed could considerably expand into the freshwater marshes of North America which cover several million hectares. The effects of common reed expansion on biodiversity are difficult to predict, but likely to be highly deleterious given the competitiveness of the invader and the biological richness of freshwater wetlands.     

Typha×glauca Godr.,香蒲属(香蒲科)中国新记录杂种及其形态特征

香蒲属(Typha L.)为多年生水生或沼生草本植物, 种间存在十分普遍的杂交现象, 其中一些杂种在湿地生态系统中有重要的作用。在查阅大量腊叶标本基础上, 结合野外居群生物学工作, 作者发现中国一新记录杂种, 即T.×glauca Godr. (T. angustifolia L.×T. latifolia L.), 并新拟“粉绿香蒲”作该杂种的中文名。对粉绿香蒲的形态特征进行了研究, 讨论了其与亲本水烛和宽叶香蒲的区别, 并给出检索表。     

Seasonal Abundance and Species Richness of Birds in Common Reed Habitats in Lake Erie

Abstract: Common reed (Phragmites australis) forms dense stands with deep layers of residual organic matter that negatively affects plant diversity and possibly habitat use by wetland birds. We sought to determine whether seasonal relative abundance and species richness of birds varied among 3 habitat types in Great Lakes coastal wetland complexes recently invaded by common reed. We used fixed-distance point counts to determine species relative abundances and species richness in edge and interior locales within common reed, cattail (Typha spp.), and meadow marsh habitats of various sizes during 2 summers (2001 and 2002) and 1 autumn (2001) at Long Point, Lake Erie, Ontario, Canada. We found that total relative abundance and species richness of birds were greater in common reed habitat compared to cattail or meadow marsh habitats. However, we also found that relative abundance of marsh-nesting birds was greater in meadow marsh habitat than in cattail and common reed during summer. Lastly, we found that, irrespective of habitat type, habitat edges had higher total relative abundance and species richness of birds than did habitat interiors. Our results show that common reed provides suitable habitat for a diversity of landbirds during summer and autumn but only limited habitat for many marsh-nesting birds during summer. Based on these results, we recommend restoration of meadow marsh habitat through reduction of common reed in Great Lakes wetlands where providing habitat for breeding marsh-nesting birds is an objective. Managers also might consider reducing the size of nonnative common reed stands to increase edge effect and use by birds, possibly including wetland birds.     

Positive interactions of the smooth cordgrass Spartina alterniflora on the mud snail Heleobia australis, in South Western Atlantic salt marshes

The role of positive interactions is often crucial in communities with intense abiotic stress such as intertidal environments. Grasses acting as ecosystem engineers, for example, may ameliorate intertidal harsh physical conditions and modify the community structure. The mud snails Heleobia australis d'Orbigny frequently inhabit the SW Atlantic marshes, mainly associated to intertidal marsh plants (mainly the smooth cordgrass Spartina alterniflora Loisel) probably due to the plant indirect effects. The purpose of this work was to investigate the magnitude of these association and the processes that generate the pattern. Samples of the snail abundance in six SW Atlantic coastal marshes show that H. australis is associated to coastal areas of low energy and low or none freshwater input. This result is important because this species is being used as bioindicator of coastal estuarine systems during the Holocene. Thus the paleontological interpretation based on this species should be revised. Within the studied areas, snails are associated to intertidal marsh plants. However, stable isotope analysis shows that neither plant nor their epiphytes are their main food sources. Field experiments show that snails actively select areas with plants, although tethering experiments show that plants do not provide shelter from predators. However, plants do buffer physical stress factors such as temperature, which generate important mortality outside plants covered areas. These positive interactions have large effects on H. australis distributions in marsh communities; increasing the habitats available for colonization and affecting their local distribution.     

Piscivory by the mummichog (Fundulus heteroclitus): Evidence from the laboratory and salt marshes

While piscivory is common in many fishes, there are few accounts for the fundulid, Fundulus heteroclitus (mummichog). We suspected that this species might be involved in several forms of piscivory including predation, cannibalism and scavenging. To evaluate these possibilities we conducted several laboratory experiments and field observations in its primary habitat, salt marshes. We found that digestion of larvae and small juveniles of F. heteroclitus was fast (< 1 h) and this makes detection of small fish prey difficult for any form of piscivory. In addition, laboratory experiments (one-on-one encounters, feeding on dead prey) indicated that both cannibalism and scavenging of conspecific prey were possible. Field observations (n = 2449 stomachs from fish 12-106 mm TL over four years at two salt marshes) also suggested that piscivory occurred frequently (4.3-24.7% of stomachs examined) based on the detection of numerous fish hard parts, especially pharyngeal jaws. These structures allowed us to determine that most prey were F. heteroclitus and to back-calculate the size of the prey and thus the piscivore/prey size relationship. As a result, it appears that both cannibalism (0.2-9.1% of stomachs) and scavenging (0.5-9.9%) are common feeding modes of F. heteroclitus in salt marshes and, subsequently, modes of energy transfer for salt marshes in general. We suggest that future studies of fish feeding consider that cannibalism and scavenging may be frequent possibilities when fish remains are detected in stomach contents.     

Nitrogen removal efficiencies in a free water surface constructed wetland in relation to plant coverage

Vegetation coverage is considered to be a key factor controlling nitrogen removal in wetlands. We describe the use of newly designed stainless steel incubation chambers to detect shifts in the in situ nitrate reduction activities associated to areas covered with common reed (Phragmites australis) and cattail (Typha latifolia) in the sediment of a free water surface constructed wetland (FWS-CW). Activities were measured at six different positions and times of the year and were related to physicochemical and hydraulic variables. Mean nitrate + nitrite reduction activities varied from 11.1 to 69.4 mg N/m²/h and showed a high variability within sediment types. Ammonification rates accounted for roughly 10% of the total nitrate reduction and were especially relevant in vegetated areas. Measured activities were highly above total nitrogen removal efficiencies estimated in the three parallel treatment cells of the Empuriabrava FWS-CW, indicating the potentiality of the system. In situ nitrate reduction activities correlated well with physichochemical characteristics such as pH and temperature. Additionally, differences in the total nitrogen removal efficiencies were detected between the three treatment cells and were related to changes in the water retention time. The plant species effect was detected in treatment cells of comparable hydraulic loads in which vegetation belts dominated by Typha latifolia were shown to have greater nitrogen removal efficiencies.     

Invasive reed effects on benthic community structure in Lake Erie coastal marshes

We examined how dominance (% canopy cover) and invasion history of common reed, Phragmites australis, affected benthic macroinvertebrate diversity and density in 8 marshes along Lake Erie’s southern shoreline. We also compared macroinvertebrate densities among patches (0.25 m²) of reed, cattail (Typha spp.), and native flora (e.g., Sagittaria, Sparganium) and epiphytic algal communities on submerged stems of reed and cattail. Narrow-leaf cattail (T. angustifolia) is also a common invasive plant to these wetlands, but does not greatly change plant community composition or ecosystem conditions like reed. Macroinvertebrate diversity (Shannon–Weaver H′) was positively related to reed cover and was highest (4.6) in two marshes with ~35- and 5-year invasion histories. Shading from high reed cover increased H′-diversity, in part, by reducing the abundance of floating duckweed, which harbored many Hyalella azteca amphipods. Percent Ephemeroptera, Odonata, and Trichoptera was low to moderate across marshes, regardless of reed cover and invasion history. Macroinvertebrate density was not affected by reed cover or average plant stem density, and did not differ among plant types. However, epiphyton densities and % diatoms were greater on reed than on cattail, suggesting reed provides a better feeding habitat for microalgal grazers than Typha. Abundance rankings of common species in these diatom-dominated communities were also typically dissimilar between these plant types. Although % grazers was unrelated to epiphyton densities and % diatoms, grazer identity (snails) differed between natural and diked marshes, which had different microalgal food supplies. Our findings suggest that Phragmites does not necessarily adversely affect macroinvertebrate community structure and diversity and that invasion history alone has little effect on the H′-diversity–reed dominance relationship.     

Known and predicted African winter distributions and habitat use of the endangered Basra reed warbler ( Acrocephalus griseldis) and the near-threatened cinereous bunting ( Emberiza cineracea)

The Basra reed warbler (Acrocephalus griseldis) and the cinereous bunting (Emberiza cineracea) are the only two Western Palearctic passerine bird species that overwinter in East Africa and are classified by BirdLife International as endangered and near-threatened, respectively. To refine the African wintering ranges of these two species, we made an effort to collect as much distributional data as possible. We then used the available point-locality data to predict the wintering distributions using a Geographic Information Systems (GIS) based inductive modelling technique called BIOCLIM. For this purpose, we developed four environmental GIS layers that are presumed to reflect the environmental preferences of migrant birds. Our data showed that the known winter distribution of the Basra reed warbler was concentrated in Kenya, Tanzania, Malawi and Mozambique, where it was usually found in dense vegetation growing in coastal scrub, woodland thickets, swamps, marshes, flooded pools and grasslands, and along ditches and edges of rivers, ponds, lagoons and lakes. The predicted winter distribution of this species includes most of East Africa but, given the habitat preferences of this species, is probably limited to low-lying areas near the coastline. The known winter distribution of the cinereous bunting is so far limited to Eritrea, where the species has been observed in October, November, February and March, in sparsely vegetated, sandy or rocky habitats on coastal plains and deserts. The predicted winter distribution of this species includes the plains and hills along the Red Sea coasts in southern Egypt, Sudan, Eritrea, Ethiopia and Sudan, as well as a few inland areas in Sudan, Ethiopia and Kenya.Communicated by F. Bairlein     

Incidence of Venturia shoot blight in aspen (Populus tremuloides Michx.) varies with tree chemistry and genotype

Quaking aspen (Populus tremuloides) is a foundation tree species in North American forests, as well as a valuable source of wood and paper products. Quaking aspen exhibits substantial genetic variation within and among natural populations in phytochemical compounds that influence both interactions with herbivores and ecosystem dynamics. The potential association of these phytochemicals with disease resistance, however, is unknown. Here we present the results of a “natural experiment” in a common garden of quaking aspen genotypes infected with shoot blight (Venturia moreletii). We found that the incidence of shoot blight varied by 10-fold among aspen genotypes, and was strongly and negatively correlated with constitutive foliar concentrations of condensed tannins. Selection factors that shape the genetic and phytochemical architecture of aspen populations may thus simultaneously influence aspen resistance to pathogen attack, with consequences for individual tree fitness as well as community organization, via “extended phenotype” effects.     

Phylogenetic position of Octosporea muscaedomesticae (Microsporidia) and its relationship to Octosporea bayeri based on small subunit rDNA analysis

Comparative phylogenetic analysis of the small subunit rDNA sequence of Octosporea muscaedomesticae (Flu, 1911) (type species) (Microsporidia) isolated from the blowfly Phormia regina (Diptera:Calliphoridae) is presented. Neighbor Joining bootstrap, Maximum Parsimony and Maximum Likelihood analyses with 38 microsporidian taxa representing five major clades of Microsporidia placed O. muscaedomesticae on a separate branch within a clade containing parasites of freshwater hosts. O. muscaedomesticae differed from Octosporea bayeri, a parasite of the microcrustacean, Daphnia magna (Cladocera:Daphniidae) by 29% demonstrating that the latter microsporidium is not closely related to the type species at the generic level, and should not be placed within the genus Octosporea, a conclusion that is further supported by morphological and developmental differences. Considering the number of disparately related hosts from which Octosporea species have been previously described based mostly on developmental and morphological characters it is likely that many will not fit the current definition of the genus, and it is possible that molecular analysis of these species will show that this genus as defined represents a polyphyletic grouping of unrelated taxa.     

Phytoremediation of selenium using subsurface-flow constructed wetland

The potential of two plant species, Phragmites australis (common reed) and Typha latifolia (cattail), in the phytoremediation process of selenium (Se) was studied in subsurface-flow constructed wetland (SSF). Se was supplemented continuously at a concentration of 100 microg Se L(-1) in the inlet of the cultivation beds of the SSF. Water samples collected from the outlet of the Phragmites bed after 1, 3, 6, 9, and 12 wk of treatments showed that Se content was under detectable limits. Water samples collected from the Typha bed at the same five periods showed that Se concentrations in the outlet were 55, 47, 65, 76, and 25 microg/L, respectively. The results of bioaccumulation in the biomass of both species after 12 wk of treatment indicated that Typha plants accumulated Se mainly in fine roots. Phragmites accumulated Se mainly in leaves and rhizomes, and moderate levels were found in stems and fine organic materials. The results indicate that common reed is a very good species for Se phytoextraction and phytostabilization (immobilization) and that cattail is only a phytostabilization species. The use of common reed and cattail for Se phytoremediation in a SSF system and in constructed wetland models are discussed.     

Buddleja davidii and Buddleja yunnanensis: Exploring features associated with commonness and rarity in Buddleja

Buddleja davidii is a widespread shrub in Asia while B. yunnanensis is a narrowly endemic species limited to Yunnan Province, China. To explore whether floral volatiles, morphological characters of flower and seed and breeding system are correlated with their distributions, we measured length and width of corolla, trichome density at corolla throat, level of stigma/anthers relationship, seed size and weight. The results indicated that these characteristics were significantly different between the two species (P < 0.01). Bagging experiments revealed that B. davidii is a self-incompatible plant while B. yunnanensis is self-compatible. Thick trichome density at the corolla throat may reduce out-crossing in B. yunnanensis. Autogamy plays an important role in fruit production of this species while B. davidii requires pollinators for fruiting. Scents were collected using dynamic headspace adsorption method and identified with coupled gas chromatography and mass spectrometry. In total, 27 floral scent compounds were identified. The volatile composition in the two species was very different. We attempted to determine if these features, associated with commonness and with rarity found in these two taxa, could also help to explain the distribution pattern of other species of the genus Buddleja.     

Methane emission from tidal freshwater marshes

In two tidal freshwater marshes, methane emission,production and accumulation in the pore-water have beenstudied. The two sites differ in their dominantvegetation, i.e., reed and bulrush, and in theirheights above sea level. The reed site was elevated inrelation to the bulrush site and had higher rates ofmethane emission and production. It is argued thatthis difference in methane emission between sites wasprimarily due to a different effect of reed andbulrush plants on methane dynamics rather than methaneoxidation related to tidal elevation. Methane emissionshowed strong seasonality related primarily to plantphysiology and only secondarily to temperature. Twocontrol sites at which vegetation was removedsystematically had lower emission rates indicating anoverall stimulating effect of plants on methaneemission from tidal marshes. Flooding reduced methaneemission, probably by blocking the primary sites ofmethane release in the lower part of the plantstems.     

Native and invasive plant interactions in wetlands and the minimal role of invasiveness

The effects of invasive plants on plants native to areas that are being invaded can be quite variable, depending on the species of the invasive plant involved as well as the physical characteristics of the location being invaded. My study focuses on the effects of Phragmites australis Linnaeus (common reed) and Lythrum salicaria L. (purple loosestrife) on the same native plant community. Uninvaded plots dominated by native plants Typha angustifolia L. (narrowleaf cattail) and Typha latifolia L. (broadleaf cattail) served as the control. I surveyed percent cover of species during early summer and midsummer for 3 years in six Hudson River freshwater tidal wetlands (sites). Differences in species richness, composition and abundance were small, but significant among invaded and uninvaded plots and among sites. However, these differences remained significant when data for dominant species (invasive and native) were removed. Differences in native plant species abundance were attributed to invasive plant species-specific characteristics and differences in species richness and composition were attributed to physical location (zonation) in these freshwater tidal marshes. “Invasive” status of a dominant plant species was less important in invasive plant–native plant interactions than species-specific characteristics and zonation. Further research into the effects of site and land-use on invasive plant impacts is recommended.     

Comparison of the diversity of root-associated bacteria in Phragmites australis and Typha angustifolia L. in artificial wetlands

Common reed (Phragmites australis) and narrow-leaved cattail (Typha angustifolia L.) are two plant species used widely in artificial wetlands constructed to treat wastewater. In this study, the community structure and diversity of root-associated bacteria of common reed and narrow-leaved cattail growing in the Beijing Cuihu Wetland, China, were investigated using 16S rDNA library and PCR–denaturing gradient gel electrophoresis methods. Root-associated bacterial diversity was higher in common reed than in narrow-leaved cattail. In both plant species, the dominant root-associated bacterial species were Alpha, Beta and Gamma Proteobacteria, including the genera Aeromonas, Hydrogenophaga, Ideonella, Uliginosibacterium and Vogesella. Acidobacteria, Actinobacteria, Nitrospirae and Spirochaetes were only found in the roots of common reed. Comparing the root-associated bacterial communities of reed and cattail in our system, many more species of bacteria related involved in the total nitrogen cycle were observed in reed versus cattail, while species involved in total phosphorus and organic matter removal were mainly found in cattail. Although we cannot determine their nutrient removal capacity separately, differences in the root-associated bacterial communities may be an important factor contributing to the differing water purification effects mediated by T. angustifolia and P. australis wetlands. Thus, further work describing the ecosystem functions of these bacterial species is needed, in order to fully understand how effective common reed- and narrow-leaved cattail-dominated wetlands are for phytoremediation.     

Identification of Mediterranean Diplodus spp. and Dentex dentex (Sparidae) by means of DNA Inter-Simple Sequence Repeat (ISSR) markers

The aim of this paper was to test the effectiveness of Inter-Simple Sequence Repeat (ISSR) technique in detecting specific molecular markers to genetically discriminate some species of teleost fish. As model species, we used four Mediterranean sea bream species (i.e. Diplodus annularis, D. puntazzo, D. sargus sargus, and D. vulgaris), and the common Mediterranean dentex Dentex dentex. Furthermore, the occurrence in our samples of two partially albino sparids (suspected, on a morphological basis, to probably belong to D. sargus sargus and to D. dentex, respectively) allowed ISSRs to be tested on doubtful specimens. Eight ISSR primers produced 95 out of 97 scorable polymorphic loci with a large number (63) of species-private bands. Maximum parsimony analysis, ΔK statistics, and assignment test were consistent in separating the five species and solving the taxonomic position of specimens of dubious attribution. The results obtained evidence the usefulness of ISSR markers in specimen and species identification, particularly when the morphological traits of fish make the classification problematic.     

Fish pathogens near the Arctic Circle: molecular,morphological and ecological evidence for unexpected diversity of Diplostomum (Digenea: diplostomidae) in Iceland

Host–parasite systems at high latitudes are promising model systems for detecting and predicting the impact of accelerated environmental change. A major challenge is the lack of baselines for the diversity and distribution of parasites in Arctic wildlife, especially in the freshwater environment. Here we present the first known estimates of the species diversity and host associations of Diplostomum spp. in sub-Arctic freshwater ecosystems of the Palaearctic. Our analyses integrating different analytical approaches, phylogenies based on mitochondrial and nuclear DNA, estimates of genetic divergence, character-based barcoding, morphological examination, precise detection of microhabitat specialisation and host use, led to the discovery of one described and five putative new species that complete their life-cycles within a fairly narrow geographic area in Iceland. This increases the species richness of Diplostomum in Iceland by 200% and raises the number of molecularly characterised species from the Palaearctic to 17 species. Our results suggest that the diversity of Diplostomum spp. is underestimated globally in the high latitude ecosystems and call for a cautionary approach to pathogen identification in developing the much needed baselines of pathogen diversity that may help detect effects of climate change in the freshwater environment of the sub-Arctic.     

Relationship between virulence and repellency of entomopathogenic isolates of Metarhizium anisopliae and Beauveria bassiana to the termite Macrotermes michaelseni

Termites encounter a diverse array of potentially useful and harmful fungi in their subterranean habitats. These vary from symbiotic to harmful species with varying levels of virulence. How these hemiedaphic insects survive in habitats with infective fungi is not well understood. Possible mediation of olfactory signals in avoiding contact with entomopathogenic fungi has been explored by a number of workers. In the present study, we initially found that Macrotermes michaelseni detected a virulent isolate of Metarhizium anisopliae from some distance and avoided direct physical contact. We hypothesized that there may be a relationship between virulence and repellency of different isolates of M. anisopliae and Beauveria bassiana to the termite. We compared these for selected isolates of the two fungi. Positive correlations between the two parameters for both sets of isolates of the fungi were obtained. The results show an interesting co-evolutionary phenomenon in which the termite's response to either M. anisopliae or B. bassiana is directly related to potential harm these fungi can inflict on the insect and that the virulent strains are more likely to be recognized from some distance and avoided.