Seasonal Fluctuation in Species Composition of Aquatic Hyphomycetous Flora in a Temperate Freshwater Stream of Central Himalaya,India

The frequency of occurrence and seasonal periodicity of aquatic hyphomycetes in a temperate freshwater stream of Central Himalaya were studied. The number of aquatic hyphomycetes species was found to vary inversely with temperature (r= −0.499; not significant), which explained 25 % of the variability. There were two maxima, one in spring and the other in autumn. On the basis of their occurrence, the species observed have been categorised into three groups. Constant species were Campylospora chaetocladia, Flagellospora penicilloides, Lemonniera aquatica and Tetracladium marchalianum.     

Response of Aquatic Leaf Associated Microbial Communities to Elevated Leachate DOC: A Microcosm Study

In Central Europe climate change will increase summer droughts, which cause both, premature leaf fall and fragmentation of small streams during summer and early autumn. As a consequence dissolved organic carbon (DOC) leached from leaves will be dispersed into pools with long water residence time. A microcosm experiment was performed to test the effect of high concentrations of leachate DOC and the relative importance of labile and refractory leachate compounds on leaf associated microbial parameters. In microcosms leaf discs colonized in a stream were exposed to high concentrations of either leaf leachate, glucose or tannic acid. Leaf associated respiration, fungal sporulation, leaf mass loss and fungal biomass (ergosterol) were measured during a 3 weeks experimental period and compared to control without DOC amendment. The results imply that depending on source and composition elevated leachate DOC may have variable effects on microbial mediated litter decomposition. Our findings suggest reduced microbial decomposition rates in pools of fragmented streams receiving premature leaf fall. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Effect of Macroinvertebrate Exclusion on Leaf Breakdown Rates in a Tropical Headwater Stream1

The role of macroinvertebrates in the process of leaf breakdown is well studied in temperate streams, but less is known about their role in the tropics. We investigated the effect of reducing macroinvertebrate access to leaf material on leaf breakdown rates in a forested headwater stream in the Luquillo Experimental Forest, Puerto Rico. We measured leaf mass loss using fine and coarse mesh bags over 12 weeks for two common riparian species: Cecropia schreberiana (Moraceae) and Dacryodes excelsa (Burseraceae). Coarse mesh allowed freshwater shrimp and other macroinvertebrates to access leaf material, while fine mesh did not. Leaf breakdown rates did not differ between C. schreberiana and D. excelsa in coarse mesh bags (?0.0375/day vs. ?0.0395/day, respectively), but C. schreberiana breakdown was significantly slower than D. excelsa in fine mesh bags (?0.0159/day vs. ?0.0266/day). Additionally, breakdown in fine mesh bags was significantly slower compared to coarse mesh bags for C. schreberiana, but less so for D. excelsa. Breakdown rates for all treatments were fast relative to those in temperate‐zone streams indicating that both macroinvertebrates and macroinvertebrate‐independent processing can strongly influence leaf decomposition in tropical streams. The difference between C. schreberiana and D. excelsa indicates that the effect of macroinvertebrate exclusion can change with leaf type.     

Colonization,Species Composition,and Conidial Production of Aquatic Hyphomycetes on Chirpine Needle Litter in a Freshwater Kumaun Himalayan Stream

Aquatic hyphomycetes colonizing the submerged chirpine (pinus roxburghii SARG .) needle litter in a high altitude, Kumaun Himalayan stream were studied. 15 species belonging to different genera of aquatic Hyphomycetes have been recognized as the colonizers of chirpine needle litter. Clavariopsis aquatica, Heliscus lugdunensis, Lunulospora cymbiformis, Triscelophorus acuminatus and T. monosporus were found with a high frequency of occurrence. The conidial production was highest in Flagellospora penicillioides, however, Campylospora chaetocladia, L. cymbiformis and T. acuminatus had less number of conidia per unit area of pine needles. The chirpine needle litter decomposition in the freshwater habitat is also discussed.     

The role of aquatic fungi in transformations of organic matter mediated by nutrients

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Leaf litter decomposition and microbial activity in nutrient-enriched and unaltered reaches of a headwater stream

SUMMARY 1. Decomposition of red maple ( Acer rubrum ) and rhododendron ( Rhododendron maximum ) leaves and activity of associated microorganisms were compared in two reaches of a headwater stream in Coweeta Hydrologic Laboratory, NC, U.S.A. The downstream reach was enriched with ammonium, nitrate, and phosphate whereas the upstream reach was not altered.
2. Decomposition rate, microbial respiration, fungal and bacterial biomass, and the sporulation rate of aquatic hyphomycetes associated with decomposing leaf material were significantly higher for both leaf types in the nutrient-enriched reach. Species richness and community structure of aquatic hyphomycetes also exhibited considerable changes with an increase in the number of fungal codominants in the nutrient-enriched reach.
3. Fungal biomass was one to two orders of magnitude greater than bacterial biomass in both reaches. Changes in microbial respiration rate corresponded to those in fungal biomass and sporulation, suggesting a primary role of fungi in leaf decomposition.
4. Nutrient enrichment increased microbial activity, the proportion of leaf carbon channelled through the microbial compartment and the decomposition rate of leaf litter.     

Leaf‐litter colonisation and breakdown in relation to stream typology: insights from Mediterranean low‐order streams

1. Scant information is available on leaf breakdown in streams of arid and semiarid regions, including the Mediterranean, where environmental heterogeneity can be high and the relationship between stream characteristics and leaf breakdown is poorly known. We tested the hypotheses that differences in leaf breakdown metrics would be substantially higher between mountain and lowland Mediterranean streams than among streams within each subregion and that variability among streams would be substantially higher in the lowlands, because permanent reaches in the semiarid lowland streams are rare and isolated. 2. We compared leaf breakdown and associated dynamics of nutrients, fungi and invertebrates in low‐order Mediterranean streams draining sub‐humid forests in the Sierra Nevada Mountains and nearby semiarid lowlands of south‐eastern Spain. Streams differed between the two subregions mainly in water ion content, temperature and riparian tree cover. We detected higher environmental heterogeneity among streams within the lowlands compared to the Sierra Nevada mountain range. In the lowlands, breakdown coefficients (k) of alder leaves spanned almost the entire range reported for this species from temperate streams, overlapping with less variable breakdown coefficients in the Sierra Nevada. 3. The high variability of k values among the lowland sites appeared to be caused primarily by variability in the composition and abundance of a few leaf‐consuming invertebrate taxa, particularly the snail Melanopsis praemorsa. Fungal and nutrient dynamics were less variable among sites within each subregion. 4. These results indicate that the critical condition for stream functional assessment of well‐constrained breakdown rates, or related metrics, could be met at reference sites within homogenous bio‐geo‐climatic regions such as the Sierra Nevada. By contrast, in heterogeneous areas such as the semiarid lowland streams, natural variability of breakdown rates can greatly exceed the magnitude of effects expected in response to anthropogenic disturbances.     

Setting Attainable Goals of Stream Habitat Restoration from a Macroinvertebrate View

Many efforts have been undertaken to reduce the impairment of stream ecosystems by wastewaters and other pollution, leading to a remarkable improvement of the water quality in most parts of Central Europe. Actually, the most severe disturbance to stream systems in Central Europe is the structural degradation of stream morphology. Restoration practices increasing the structural heterogeneity of formerly degraded stream sections are necessary to create new habitats at different scales that could provide habitat for a diverse invertebrate community. Increasing biodiversity of aquatic invertebrates strengthens the ecological integrity of streams and is therefore a desirable goal in stream restoration. Nevertheless, recent studies focusing on the effect of structural restoration of stream sections often displayed results that did not really met the preset goal of increasing invertebrate diversity. This might be due to sometimes severe disturbance caused by the restoration practice itself, impairing the established invertebrate community in the restored stream section. Additionally, the potential for immigration of new species into the restored stream section is often limited. Therefore, several important prerequisites must be accounted for in the planning of restoration practices to improve structurally degraded stream sections, when the goal of restoration is increasing invertebrate diversity.     

Decomposition of leaf litter of Dombeya goetzenii in the Njoro River, Kenya

Decomposition of the leaves of Dombeya goetzenii (K. Schum) in the Njoro River is described and analysed. The loss of the ash-free dry mass was rapid during the first 14 d of exposure in the wet and humid zones. The leaves in the litter bags in the humid and wet zones were processed at a rate (±SD) of 0.005±0.001 d^-1 and 0.021±0.001 d^-1, respectively. The processing rates of the leaves in the wet zone differed significantly from those observed in the humid zone (t-value, p<0.05). The interchanged litter bags (i.e. from wet to humid zones vice versa) showed that the processing rates of the leaves in the litter bags interchanged from the wet zone to the humid zone was about 200 times lower than that of the leaves retained in the wet zone throughout; fourfold higher in the leaves in the litter bags which were transferred to the wet zone than in those leaves of the litter bags which were retained in the humid zone throughout the experiment. It took approximately 38 months for 90% of the leaf dry mass to be processed in the humid zone whilst it took 4 months for a similar percentage to be processed in the wet zone. It is concluded that the immersion and emersion of leaf litter, which may occur in the wet and humid zones, respectively, are important aspects of the decomposition process which may influence the quantity of nutrients in stream ecosystems.     

Factors Affecting the Benthic Community Structure of a Discontinuous Stream in Guadelupe Mountains National Park,Texas

McKittrick Creek, a discontinuous mountain-desert stream in Guadelupe Mountains National Park, Texas, was sampled at discrete locations (pools) to test for differences in biomass, density, species diversity, equitability, and species richness in the benthic macroinvertebrate community. Significant differences occurred among pools for these biotic characteristics of the benthic community along the downstream gradient. Pools connected by flow were more similar to each other than pools separated by dry reaches. Variation in the quantity of coarse detritus and periphyton best explained differences among pools.     

The Role of Early Fungal Colonizers in Leaf‐Litter Decomposition in Portuguese Streams Impacted by Agricultural Runoff

We conducted a transplant experiment between two streams in NW Portugal impacted by agricultural runoff, mainly differing in phosphate concentration, to determine whether fungi on decomposing leaves would adapt to the new environment or would be replaced by fungi of the recipient stream. The most nutrient enriched stream had lower fungal diversity but faster leaf decomposition. Leaf transplantation did not alter fungal activity or species dominance. Multidimensional scaling ordination of fungal communities, from DNA fingerprint or conidial production, revealed that transplanted communities resembled more those of the original stream than the recipient stream. Results suggest that early fungal colonizers will determine the development and activity of fungal communities on decomposing leaves in streams impacted by agricultural practices. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quantification of the Nitrogen Cycle in a Prairie Stream

Nitrogen (N) was added for 35 days in the form of ¹⁵NH₄Cl to Kings Creek on Konza Prairie, Kansas. Standing stocks of N in key compartments (that is, nutrients, detritus, organisms) were quantified, and the amount of labeled N entering the compartments was analyzed. These data were used to calculate turnover and flux rates of N cycling through the food web, as well as nutrient transformation rates. Inorganic N pools turned over much more rapidly in the water column of this stream than in pelagic systems where comparable measurements have been made. As with other systems, the mass of ammonium was low but it was the key compartment mediating nutrient flux through the ecosystem, whereas dissolved organic N, the primary component of N flux through the system, is not actively cycled. Nitrification was also a significant flux of N in the stream, with rates in the water column and surface of benthos accounting for approximately 10% of the total ammonium uptake. Primary consumers assimilated 67% of the inorganic N that entered benthic algae and microbes. Predators acquired 23% of the N that consumers obtained. Invertebrate collectors, omnivorous crayfish (Orconectes spp.), and invertebrate shredders dominated the N flux associated with primary consumers. Mass balance calculations indicated that at least 23% of the 309 mg of ¹⁵N added during the 35 days of release was retained within the 210-m stream reach during the release. Overall, the rates of turnover of N in organisms and organic substrata were significantly greater when C:N was low. This ratio may be a surrogate for biological activity with regard to N flux in streams. Received 2 August 1999; accepted 18 July 2000.     

Leaf Litter Decomposition of Three Riparian Tree Species and Associated Macroinvertebrates of Eswathu Oya,a Low Order Tropical Stream in Sri Lanka

Leaf decomposition, an important component of the organic matter dynamics in streams, has been widely examined in temperate regions but much less documented in tropical regions. We report here the first study of leaf decomposition in a Sri Lankan stream. The litterbag technique was used. Coarse (8 mm) and fine (100 µm) litterbags, that included or excluded macroinvertebrates respectively, were used to enclose leaves of three dominant riparian tree species: native Ochlandra stridula (bamboo), and the introduced Alstonia macrophylla and Hevea brasiliensis (rubber). A fourth set of litterbags contained a mixture of these three species. Leaf colonization by macroinvertebrates was highest in the early stages of the decomposition process on Hevea leaves but invertebrate densities declined later. The opposite colonization effect was observed on the native Ochlandra leaves: slow colonization with continuing low densities from the beginning to the end of the process. Decomposition of all three species was significantly faster in the coarse than in the fine mesh bags. Alstonia, which has the softest leaf tissue, was most rapidly decomposed while Ochlandra, with its tough structure, was the slowest. Among the invertebrates, insects were the most important leaf colonizing animals, with Diptera, Coleoptera and Trichoptera the most dominant. The invertebrate variety in the mixed bags was higher than in the single‐species leaf bags, where Chironomidae dominated the colonizing assemblages. This study has shown that toughness, indicated by the ‘specific weight of leaf tissue’, and the quality of the leaves was more important in determining breakdown rates than their origin. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of Zn,Fe and Mn on Leaf Litter Breakdown by Aquatic Fungi: a Microcosm Study

We investigated the effects of heavy metals on leaf litter decomposition in streams. Leaves were immersed (10 days) at a reference (R) and a metal‐impacted (I) site and exposed in microcosms with increased Zn, Mn or Fe content, and to stream water from site R or I. Fungal biomass was higher in microcosms with leaves colonized at I and water from R. Fungal sporulation was higher in microcosms with leaves and water from R. Concentrations of 4.9, 9.6 and 5 ppm of Zn, Mn and Fe decrease fungal sporulation. The number of fungal species (spore counts and DGGE fingerprints) was lower in leaves colonized at site I. Cluster analyses of DGGE showed that Fe was the metal that most altered the structure of fungal community. Our results suggest that metal pollution affect leaf‐associated fungi depending on metal identity and concentration, and effects appear to be less pronounced in metal‐adapted communities. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Aquatic hyphomycetes of a sulphur spring

Aquatic hyphomycetes of a sulphur spring in the Western Ghat region of Karnataka were investigated by the following methods: leaf litter observations, water filtration, analysis of natural and induced foam. The samples were collected and studied from three sites, the spring proper (site I), the connecting region of the spring and the rivulet (site II) and the spot where the spring joins the rivulet (site III). The number of species of hyphomycetes encountered at the three sites were 1, 14 and 20, respectively. The sulphide content of the spring ranged between 0.1–3.1 mg l^–1 and the temperature between 26.5–36.5 °C. In another experiment submerged coffee leaves from a fresh water stream were collected and incubated in spring water, stream water and well water at different temperatures (16–40 °C). A maximum of 18 species of hyphomycetes sporulated at 22 °C followed by 17 species at 28 °C, irrespective of the source of water in which the leaves were incubated. Based on these studies, we conclude that the presence of only one species in the spring proper (site I) was not due to the higher sulphide content, but to the high temperature.     

Effects of Leaf Litter Species on Macroinvertebrate Colonization during Decomposition in a Portuguese Stream

This study evaluated if there are differences in leaf breakdown and invertebrate colonization among tree species differing in quality (toughness), and which factors could influence these differences. Common alder leaves decomposed significantly faster then either sweet chestnut or Spanish oak (k values of –0.0332, –0.0108, and –0.0112, respectively) during the first 2 months. Shredder abundance was highest when leaf mass remaining was 50%, and the samples clustered in mixed groups of sampling dates and leaf species, suggesting that stage of decomposition was an important factor influencing shredder colonization. During the first two months of decomposition, the physicochemical characteristics of leaf litter and the interaction between leaf toughness and the occurrence of frequent spates seemed to be the main factors affecting leaf breakdown rates in the stream. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Leaf litter decomposition in remote oceanic island streams is driven by microbes and depends on litter quality and environmental conditions

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Fungi and aflatoxins associated with spices in the Sultanate of Oman

One hundred and five samples of seven spices (cumin, cinnamon, clove, black pepper, cardamom, ginger, and coriander) were purchased from five popular companies in the Sultanate of Oman. The spices were surveyed for the mycoflora and aflatoxins. Twenty fungal species were isolated in which Aspergillus flavus , A. niger . Penicillium , Rhizopus , and Syncephalastrum racemosum were the most dominant. When colony forming units per gm (cfu/gm) of fungi were compared, significant differences were found among spices and companies. Of the seven spices studied, clove was found to be the least contaminated, while cumin was the most contaminated. None of the 15 selected samples of the spices contaminated by A. flavus were found to contain aflatoxins. Nevertheless, nine isolates (45%) of the twenty A. flavus strains screened for aflatoxins were aflatoxigenic. The moisture content of most of the spices was below the maximum standard limit. The results showed that the spices were contaminated by some fungi that might constitute health hazards for humans. This revised version was published online in June 2006 with corrections to the Cover Date.     

Characterization of Microbial Mats from a Desert Wadi Ecosystem in the Sultanate of Oman

Desert wadis are widespread in the Arabian Peninsula and play a vital role in the ecology of the region; nevertheless, these ecosystems are among the least studied. Various types of microbial mats are predominant in wadis, but information on their bacterial diversity and spatial distribution is very scarce. We investigated bacterial diversity, pigments and lipid composition of ten mats located at the down-, mid- and upstream of a desert wadi in Oman. Direct microscopy revealed the existence of different unicellular and filamentous cyanobacteria, with the dominance of the heterocystous genera Calothrix and Scytonema. The majority of MiSeq 16S rRNA sequences (44-76%) were affiliated to Cyanobacteria and Proteobacteria. While Alphaproteobacteria was the most dominant proteobacterial class (10 to 48% of total sequences), Gamma- and Deltaproteobacteria were subdominant. Cluster analysis showed that the mats’ bacterial communities at the different locations along the wadi were different and shared less than 60% of their operational taxonomic units (OTUs). Chlorophyll a and scytonemin were the most predominant pigments in all mats. Different saturated, branched and mono- and poly-unsaturated fatty acids were detected in all mats, with C₁₆ and C₁₈ compounds as most dominant. The detected pigments and fatty acids indicate a major role of cyanobacteria in the wadi mats and the adaptation of microorganisms therein to the harsh wadi environment. Detection of diadinoxanthin and fucoxanthin confirmed the presence of diatoms. We conclude that microbial mats are important elements in wadi ecosystems and exist in a great variety of structure and community composition.