Response of aquatic hyphomycete communities to enhanced stream retention in areas impacted by commercial forestry

1. Aquatic hyphomycetes are an important component of detritus processing in streams. Their response to enhanced stream retentiveness was tested by manipulating three streams located in Kielder Forest (northern England), a large plantation of exotic conifers, and two streams in Montagne Noire (south-west France) dominated by native broadleaf woodland. Treatment was by placement of logs or plastic litter traps into a 10–20 m stream section. Fungal spores were collected from stream water upstream and downstream of the treated sections over 1–2 years. 2.The average concentration of fungal spores in reference sections was nearly 10x greater in the French streams than in the English streams. The number of hyphomycete species was also higher in the French streams. These differences between regions were probably a consequence of the much lower standing stock and diversity of leaf litter in the English streams. 3. Despite these large regional differences, the treatment had a clear effect in all streams. Detrital standing stocks were enhanced in treated sections by up to 90% in French streams and 70% in English streams. 4. Mean spore density below treated sections increased by 1.8–14.8% in French streams and 10.2–28.9% in the naturally less retentive English streams. The number of fungal species increased significantly below the treated sections of the English streams, although not the French ones. 5. In biologically impoverished plantation streams, input of woody debris can increase detritus retention and enhance hyphomycete diversity and productivity. This may have consequent benefits for detritus processing and macroinvertebrate production

Genetic diversity in Tetrachaetum elegans, a mitosporic aquatic fungus.

Tetrachaetum elegans Ingold is a saprobic aquatic hyphomycete for which no sexual stage has yet been described. It occurs most commonly during the initial decay of tree leaves in temperate freshwater habitats and typically sporulates under water. Dispersal of the aquatic fungus takes place primarily in the water column and has a large passive component. Differences in substrate composition (e.g. quality of leaf litter) may also play a role in the distribution of different species or genotypes. The population genetic structure of T. elegans was studied using amplified fragment length polymorphism (AFLP) multilocus fingerprints. The populations were isolated from the leaf litter of three different tree genera, sampled in nine streams distributed throughout a mixed deciduous forest. Molecular markers were developed for 97 monosporic isolates using four selective primer pairs. A total of 247 fragments were scored, of which only 32 were polymorphic. Significant stream differentiation was detected for the isolates considered in this study. Analysis of molecular variance revealed that 20% of the genetic variation observed was the result of differences between streams. No correlation between genetic and geographical distances was found but a few multilocus genotypes were observed in different locations. Altogether these results suggest that environmental barriers play a role in the population structure of this aquatic fungus. No clear-cut effect of leaf litter composition on genetic variation could be demonstrated. Finally, tests of linkage disequilibrium between the 32 polymorphic AFLP loci as well as simulations did not provide a final answer regarding clonality in T. elegans. Indeed, it was possible to reject linkage equilibrium at different sampling levels and show that full linkage was unlikely

Processus écologiques et évolutifs influençant la colonisation de l'ambroisie à feuilles d'armoise (Ambrosia artemisiifolia L.) en France

La compréhension des mécanismes déterminant le succès des espèces invasives est une étape essentielle dans la gestion des invasions biologiques actuelles et la prédiction des futurs risques d invasion. En adoptant un cadre d étude conceptuel intégrant les processus écologiques et évolutifs, l objectif de ce travail était d analyser les déterminants de la colonisation de l ambroisie à feuilles d armoise en France. Tout d abord, l étude des interactions biotiques et abiotiques a permis de montrer la capacité de tolérance de l ambroisie à l herbivorie et au stress hydrique. L ambroisie est capable de tolérer la défoliation grâce à une croissance compensatoire efficace, sans que sa reproduction en soit affectée. Cette forte tolérance à l herbivorie est maintenue chez les populations introduites, malgré la faible pression des ennemis naturels dans la zone d introduction. En condition de stress hydrique, l ambroisie produit une biomasse racinaire supérieure aux espèces présentes dans les communautés qu elle envahit. De plus, les différences dans les valeurs moyennes pour les traits mesurés suggèrent une occupation différente par l ambroisie des niches écologiques disponibles. La comparaison en jardins communs de populations de l aire d origine avec des populations de l aire d introduction isolées et issues du foyer central d invasion a montré que l adaptation de l ambroisie à son environnement reposait principalement sur la plasticité phénotypique plutôt que sur la différenciation des traits. Les études de génétiques quantitatives ont mis en évidence un potentiel évolutif élevé pour les traits liés à la germination. Les traits liés à la morphologie, à la phénologie et à la physiologie de la plante montrent une variance additive et une héritabilité plus faibles et donc un potentiel évolutif moindre. En revanche, la variation dans les normes de réaction indique un potentiel évolutif important de la plasticité phénotypique. La tolérance au stress hydrique et à l herbivorie sont des facteurs qui potentiellement augmentent la capacité de l ambroisie à coloniser une large gamme d habitat. De plus, la plasticité phénotypique et le potentiel évolutif important peuvent favoriser une augmentation ou un déplacement de la niche écologique de l espèce et ainsi favoriser l expansion de son aire de répartitionUnderstanding of the mechanisms behind the success of the invasive species is essential to manage current biological invasions and to prevent the risks of the futures ones. Using a conceptual framework integrating ecological and evolutionary processes, this work aimed to analyse the factors of the common ragweed colonization in France. First of all, the study of biotic and abiotic interactions has shown the ability of common ragweed to tolerate herbivory and water stress. Common ragweed is able to buffer defoliation through an efficient compensatory growth with no consequence on the reproduction. Herbivory tolerance has been maintained in introduced populations even if herbivory pressure is low in the introduction area. Under water stress conditions, common ragweed displayed higher root biomass than the other species present in the communities it invades. In addition, differences in mean trait values suggest different niche occupation by common ragweed compared with its companion species. Common garden experiments comparing native populations vs. invasive isolated and invasive core populations have shown that adaptation ability is mainly due to phenotypic plasticity rather than trait differentiations. Quantitative genetic studies suggest a high evolutionary potential for germination traits. Morphological, phenological and physiological traits exhibit lower standard genetic variation and lower heritability and thus a lower evolutionary potential. However, variation in reaction norms suggests a high evolutionary potential for phenotypic plasticity. Herbivory and water stress tolerance are factors that potentially increase the ability to colonize à large range of habitats. Furthermore, phenotypic plasticity and evolutionary potential may also favour an increase or a shift in species ecological niche and hence may favour the distribution range expansionDIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Diversity and functions of leaf-decaying fungi in human-altered streams

1. Stream conditions have been evaluated using leaf breakdown, and aquatic hyphomy- cetes are a diverse group of fungal decomposers which contribute to this process. 2. In field surveys of three pairs of impact-control stream sites we assessed the effect of eutrophication, mine pollution and modification of riparian vegetation on alder leaf breakdown rate in coarse and fine mesh bags and on mycelial biomass, spore production and species diversity of leaf-colonizing fungi. 3. In addition, we gathered published information on the response of leaf-colonizing fungi to these three types of perturbations. We conducted a meta-analysis of 23 published papers to look for consistent patterns across studies and to determine the relevance of four fungal- based metrics (microbial breakdown rate, maximum spore production, maximum mycelial biomass and total species richness) to detect stream impairment. 4. In our field surveys, leaf breakdown rates in coarse mesh bags were lower at impact than at paired control sites regardless of perturbation type. A similar trend was observed for leaf breakdown rates in fine mesh bags. Mycelial biomass and spore production were higher in the eutrophied stream than in the control stream. Spore production was depressed in the mine polluted stream, while it was slightly enhanced in the stream affected by forestry. Fungal diversity tended to be lower at impact than at paired control sites, though the mean and cumulative species richness values were often inconsistent. 5. Results of the meta-analysis confirmed that mine pollution reduces fungal diversity and performance. Eutrophication was not found to affect microbial breakdown rate, maximum spore production and maximum mycelial biomass in a predictable manner because both positive and negative effects were reported in the literature. However, fungal species richness was consistently reduced in eutrophied streams. Modification of riparian vegetation had at most a small stimulating effect on maximum spore production. Among the four fungal-based metrics included in the meta-analysis, maximum spore production emerged as the most sensitive indicator of human impact on streams. 6. Taken together, our findings indicate that human activities can affect the diversity and functions of aquatic hyphomycetes in streams. We also show that leaf breakdown rate and simple fungal-based metrics, such as spore production, are relevant to assess stream condition

Biological Flora of the British Isles: Ambrosia artemisiifolia

1. This account presents information on all aspects of the biology of Ambrosia artemisiifolia L. (Common ragweed) that are relevant to understanding its ecology. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, and history, conservation, impacts and management. 2. Ambrosia artemisiifolia is a monoecious, wind-pollinated, annual herb native to North America whose height varies from 10 cm to 2.5 m, according to environmental conditions. It has erect, branched stems and pinnately lobed leaves. Spike-like racemes of male capitula composed of staminate (male) florets terminate the stems, while cyme-like clusters of pistillate (female) florets are arranged in groups in the axils of main and lateral stem leaves. 3. Seeds require prolonged chilling to break dormancy. Following seedling emergence in spring, the rate of vegetative growth depends on temperature, but development occurs over a wide thermal range. In temperate European climates, male and female flowers are produced from summer to early autumn (July to October). 4. Ambrosia artemisiifolia is sensitive to freezing. Late spring frosts kill seedlings and the first autumn frosts terminate the growing season. It has a preference for dry soils of intermediate to rich nutrient level. 5. Ambrosia artemisiifolia was introduced into Europe with seed imports from North America in the 19th century. Since World War II, it has become widespread in temperate regions of Europe and is now abundant in open, disturbed habitats as a ruderal and agricultural weed. 6. Recently, the North American ragweed leaf beetle (Ophraella communa) has been detected in southern Switzerland and northern Italy. This species appears to have the capacity to substantially reduce growth and seed production of A. artemisiifolia. 7. In heavily infested regions of Europe, A. artemisiifolia causes substantial crop-yield losses and its copious, highly allergenic pollen creates considerable public health problems. There is a consensus among models that climate change will allow its northward and uphill spread in Europe

Plant litter diversity affects invertebrate shredder activity and the quality of fine particulate organic matter in streams

Draft. Published online 06 January 2015There is evidence that loss of riparian plant diversity alters the availability and quality of resources in streams, but little is known about how such effects change with time after loss of diversity. We used a microcosm approach with leaves of alder, oak and eucalypt previously colonised by microbes in a mixed forest stream to test how loss of litter diversity and time (2 and 6 months after loss of diversity) affect leaf consumption by invertebrate shredders, the elemental composition of shredder tissues, and the quality of fine particulate organic matter (FPOM). The number and identity of leaf species affected leaf consumption and FPOM production by shredders. Effects of leaf species diversity were positive and became more frequent with time after loss of diversity. Carbon (C) and nitrogen (N) composition of invertebrate tissues changed with the leaf identity. FPOM quality (C:N ratio) was positively correlated with leaf quality. Leaf consumption by the animals decreased linearly with the increase in C:N imbalance between leaf litter and invertebrate tissues. Our results suggest that changes in plant litter diversity affect the activity of shredders (leaf consumption and FPOM production), and the quality of food resources (FPOM and shredders) to higher trophic levels in streams; such effects are likely to become stronger with time after loss of plant diversity.The European Regional Development Fund – Operational Competitiveness Program (FEDER-POFC-COMPETE) and the Portuguese Foundation for Science and Technology (FCT) supported this study (PEst-OE/BIA/UI4050/2014, PTDC/AAC-AMB/117068/2010), I. Fernandes (SFRH/BD/42215/2007) and S. Duarte (SFRH/BPD/47574/2008

Effects of riparian plant diversity loss on aquatic microbial decomposers become more pronounced at longer times

We examined the potential long-term impacts of riparian plant diversity loss on diversity and activity of aquatic microbial decomposers. Microbial assemblages were obtained in a mixed-forest stream by immersion of mesh bags contain-ing three leaf species (alder, oak and eucalyptus), commonly found in riparian corridors of Iberian streams. Simulation of species loss was done in microcosms by including a set of all leaf species, retrieved from the stream, and non-colonized leaves of three, two or one leaf species. Leaves were renewed every month throughout six months, and microbial inoculum was ensured by a set of colonized leaves from the previous month. Microbial diversity, leaf mass loss and fungal biomass were assessed at the second and sixth months after plant species loss. Molecular diversity of fungi and bacteria, as the total number of operational taxonomic units per leaf diversity treatment, decreased with leaf diversity loss. Fungal biomass tended to decrease linearly with leaf species loss on oak and eucalyptus, suggesting more pronounced effects of leaf diver-sity on lower quality leaves. Decomposition of alder and eucalyptus leaves was affected by leaf species identity, mainly after longer times following diversity loss. Leaf decomposi-tion of alder decreased when mixed with eucalyptus, while decomposition of eucalyptus decreased in mixtures with oak. Results suggest that the effects of leaf diversity on microbial decomposers depended on leaf species number and also on which species were lost from the system, especially after longer times. This may have implications for the management of riparian forests to maintain stream ecosystem functioning.FEDER-POFC-COMPETE and the Portuguese Foundation for Science and Technology supported this study (PEst-C/ BIA/UI4050/2011, PTDC/AAC-AMB/113746/2009 and PTDC/AAC-AMB/117068/2010), S. Duarte (SFRH/BPD/47574/2008) and I. Fernandes (SFRH/BD/42215/2007)

Intraspecific Variation of the Aquatic Fungus Articulospora tetracladia: An Ubiquitous Perspective

The worldwide-distributed aquatic fungus Articulospora tetracladia Ingold is a dominant sporulating species in streams of the Northwest Iberian Peninsula. To elucidate the genetic diversity of A. tetracladia, we analyzed isolates collected from various types of plant litter or foam in streams from North and Central Portugal and North Spain, between 2000 and 2010. Genetic diversity of these fungal populations was assessed by denaturing gradient gel electrophoresis (DGGE) fingerprints and by using ITS1-5.8S-ITS2 barcodes. Moreover, ITS1-5.8S-ITS2 barcodes of A. tetracladia reported in other parts of the world (Central Europe, United Kingdom, Canada, Japan and Malaysia) were retrieved from the National Center for Biotechnology (NCBI) and the National Institute of Technology and Evaluation Biological Resource Center (NBRC) to probe into genetic diversity of A. tetracladia. PCR-DGGE of ITS2 region of 50 Iberian fungal isolates distinguished eight operational taxonomic units (OTUs), which were similar to those obtained from neighboring trees based on ITS2 gene sequences. On the other hand, ITS1-5.8S-ITS2 barcodes of 68 fungal isolates yielded nine OTUs, but five fungal isolates were not assigned to any of these OTUs. Molecular diversity was highest for OTU-8, which included only European isolates. Two haplotypes were observed within OTU-8 and OTU-9, while only one haplotype was found within each of the remaining OTUs. Malaysia did not share haplotypes with other countries. Overall results indicate that, apart from the Malaysian genotypes, A. tetracladia genotypes were geographically widespread irrespective of sampling time, sites or substrates. Furthermore, PCR-DGGE appeared to be a rapid tool for assessing intraspecific diversity of aquatic hyphomycetes

Vegetation diversity increases species richness of leaf-decaying fungal communities in woodland streams

Submerged leaf litter is a vital resource for many aquatic species in wood- land streams. However, forestry tends to lower the diversity of litter entering streams, which potentially impacts leaf-dependent species and the entire detritus-based food web. To overcome this problem, a guideline for sustainable forestry and ecosystem conservation lies in increasing litter diversity in managed forests. However, the way in and the extent to which such an increase changes the leaf decomposer communities are mostly unknown. In the present study, fungal communities were surveyed bimonthly in ten woodland headwater streams with contrasting tree diversity resulting in various proportions of leaf species in litter. A total of 79 aquatic hyphomycete species identified from conidia in stream water were listed. The differences in conidial abundance, richness and diversity between communities from the ten streams suggested a strong effect of local abundance and composition of leaf litter. Conidial abundance clearly distinguished two sets of streams, one dominated by oaks and hazel and the other by beech. The fungal richness in the ten streams showed a positive and significant correlation with the leaf species richness, accounting for 44 % of the total variance among streams. About 50 % more fungal species were found in streams with the highest leaf litter diversity, and several species were more frequent in such streams. No distinct species assemblages were however associated with any particular leaf species. These findings were interpreted as resulting from substrate preferences, but not specificity by the fungal species. This is supported by a manipulation in which the addition of a bulk of hazel leaves in a stream dominated by beech did not result in an increase in fungal richness over three months. Seasonal changes appeared to be the main factor controlling fungal species abundance. Overall, the results suggest a hierarchical pattern between riparian and aquatic biodiversity and provide an argument for the conservation of diverse tree species along streams