RESUMEN
Identifying nonpoint phosphorus (P) sources in a watershed is essential for addressing cultural eutrophication and for proposing best-management solutions. The oxygen isotope ratio of phosphate (δ18OPO4) can shed light on P sources and P cycling in ecosystems. This is the first assessment of the δ18OPO4 distribution in a whole catchment, namely, the Yasu River Watershed in Japan. The observed δ18OPO4 values in the river water varied spatially from 10.3 to 17.6. To identify P sources in the watershed, we used an isoscape approach involving a multiple-linear-regression model based on land use and lithological types. We constructed two isoscape models, one using data only from the whole watershed and the other using data from the small tributaries. The model results explain 69% and 96% of the spatial variation in the river water δ18OPO4. The lower R2 value for the whole watershed model is attributed to the relatively large travel time for P in the main stream of the lower catchment that can result in cumulative biological P recycling. Isoscape maps and a correlation analysis reveal the relative importance of P loading from paddy fields and bedrock. This work demonstrates the utility of δ18OPO4 isoscape models for assessing nonpoint P sources in watershed ecosystems.
Asunto(s)
Fosfatos , Fósforo , Ecosistema , Monitoreo del Ambiente , Japón , OxígenoRESUMEN
Plant litter breakdown is a key ecological process in terrestrial and freshwater ecosystems. Streams and rivers, in particular, contribute substantially to global carbon fluxes. However, there is little information available on the relative roles of different drivers of plant litter breakdown in fresh waters, particularly at large scales. We present a global-scale study of litter breakdown in streams to compare the roles of biotic, climatic and other environmental factors on breakdown rates. We conducted an experiment in 24 streams encompassing latitudes from 47.8° N to 42.8° S, using litter mixtures of local species differing in quality and phylogenetic diversity (PD), and alder (Alnus glutinosa) to control for variation in litter traits. Our models revealed that breakdown of alder was driven by climate, with some influence of pH, whereas variation in breakdown of litter mixtures was explained mainly by litter quality and PD. Effects of litter quality and PD and stream pH were more positive at higher temperatures, indicating that different mechanisms may operate at different latitudes. These results reflect global variability caused by multiple factors, but unexplained variance points to the need for expanded global-scale comparisons.
Asunto(s)
Biodegradación Ambiental , Plantas , Ríos , Biodiversidad , Biota , Ciclo del Carbono , Clima , Ecosistema , Concentración de Iones de Hidrógeno , FilogeniaRESUMEN
Relationships between environmental factors and bacterial communities were investigated in 41 freshwater lakes located in mountainous regions of eastern Japan. Bacterioplankton community composition (BCC) was determined by polymerase chain reaction-denaturing gradient gel electrophoresis of the 16S rRNA gene and then evaluated on the basis of physicochemical and biological variables of the lakes. Canonical correspondence analysis revealed that BCC of oligotrophic lakes was significantly influenced by dissolved organic carbon (DOC) content, but its effect was not apparent in the analysis covering all lakes including mesotrophic and eutrophic ones. The generalized linear model showed the negative association of DOC on the taxon richness of bacterioplankton communities. DOC was positively correlated with the catchment area per lake volume, suggesting that a large fraction of DOC supplied to the lake was derived from terrestrial sources. These results suggest that allochthonous DOC has a significant effect on bacterioplankton communities especially in oligotrophic lakes. The genus Polynucleobacter was detected most frequently. The occurrence of Polynucleobacter species was positively associated with DOC and negatively associated with total phosphorus (TP) levels. In addition, TP had a stronger effect than DOC, suggesting that oligotrophy is the most important factor on the occurrence of this genus.
Asunto(s)
Bacterias/aislamiento & purificación , Bacterias/metabolismo , Carbono/metabolismo , Lagos/microbiología , Plancton/aislamiento & purificación , Plancton/metabolismo , Bacterias/clasificación , Bacterias/genética , Ecosistema , Japón , Lagos/química , Datos de Secuencia Molecular , Filogenia , Plancton/clasificación , Plancton/genética , Microbiología del AguaRESUMEN
The decomposition of plant litter is one of the most important ecosystem processes in the biosphere and is particularly sensitive to climate warming. Aquatic ecosystems are well suited to studying warming effects on decomposition because the otherwise confounding influence of moisture is constant. By using a latitudinal temperature gradient in an unprecedented global experiment in streams, we found that climate warming will likely hasten microbial litter decomposition and produce an equivalent decline in detritivore-mediated decomposition rates. As a result, overall decomposition rates should remain unchanged. Nevertheless, the process would be profoundly altered, because the shift in importance from detritivores to microbes in warm climates would likely increase CO(2) production and decrease the generation and sequestration of recalcitrant organic particles. In view of recent estimates showing that inland waters are a significant component of the global carbon cycle, this implies consequences for global biogeochemistry and a possible positive climate feedback.
Asunto(s)
Agua Dulce , Hojas de la Planta/metabolismo , Ciclo del Carbono , Dióxido de Carbono , Secuestro de Carbono , Cambio Climático , Ecosistema , Plantas/metabolismo , TemperaturaRESUMEN
Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low and high functional diversity in 40 streams on 6 continents and spanning 113° of latitude. Despite important variability in our dataset, we found latitudinal differences in the effect of litter functional diversity on decomposition, which we explained as evolutionary adaptations of litter-consuming detritivores to resource availability. Specifically, a balanced diet effect appears to operate at lower latitudes versus a resource concentration effect at higher latitudes. The latitudinal pattern indicates that loss of plant functional diversity will have different consequences on carbon fluxes across the globe, with greater repercussions likely at low latitudes.
RESUMEN
The relationship between detritivore diversity and decomposition can provide information on how biogeochemical cycles are affected by ongoing rates of extinction, but such evidence has come mostly from local studies and microcosm experiments. We conducted a globally distributed experiment (38 streams across 23 countries in 6 continents) using standardised methods to test the hypothesis that detritivore diversity enhances litter decomposition in streams, to establish the role of other characteristics of detritivore assemblages (abundance, biomass and body size), and to determine how patterns vary across realms, biomes and climates. We observed a positive relationship between diversity and decomposition, strongest in tropical areas, and a key role of abundance and biomass at higher latitudes. Our results suggest that litter decomposition might be altered by detritivore extinctions, particularly in tropical areas, where detritivore diversity is already relatively low and some environmental stressors particularly prevalent.
Asunto(s)
Biota , Ecosistema , Ríos , Animales , Biodiversidad , Biomasa , Tamaño Corporal , Chironomidae/fisiología , Clima , Ephemeroptera/fisiología , Insectos/fisiología , Hojas de la Planta/química , Bosque Lluvioso , Ríos/química , Ríos/microbiología , Ríos/parasitología , Ríos/virología , Clima Tropical , TundraRESUMEN
The effect of resource subsidies on recipient food webs has received much recent attention. The purpose of this study was to measure the effects of significant seasonal seaweed deposition events, caused by hurricanes and other storms, on species inhabiting subtropical islands. The seaweed represents a pulsed resource subsidy that is consumed by amphipods and flies, which are eaten by lizards and predatory arthropods, which in turn consume terrestrial herbivores. Additionally, seaweed decomposes directly into the soil under plants. We added seaweed to six shoreline plots and removed seaweed from six other plots for three months; all plots were repeatedly monitored for 12 months after the initial manipulation. Lizard density (Anolis sagrei) responded rapidly, and the overall average was 63% higher in subsidized than in removal plots. Stable-isotope analysis revealed a shift in lizard diet composition toward more marine-based prey in subsidized plots. Leaf damage was 70% higher in subsidized than in removal plots after eight months, but subsequent damage was about the same in the two treatments. Foliage growth rate was 70% higher in subsidized plots after 12 months. Results of a complementary study on the relationship between natural variation in marine subsidies and island food web components were consistent with the experimental results. We suggest two causal pathways for the effects of marine subsidies on terrestrial plants: (1) the "fertilization effect" in which seaweed adds nutrients to plants, increasing their growth rate, and (2) the "predator diet shift effect" in which lizards shift from eating local prey (including terrestrial herbivores) to eating mostly marine detritivores.
Asunto(s)
Artrópodos/fisiología , Cadena Alimentaria , Lagartos/fisiología , Algas Marinas , Animales , Conducta Alimentaria , Factores de TiempoRESUMEN
Interfaces between terrestrial and stream ecosystems often enhance species diversity and population abundance of ecological communities beyond levels that would be expected separately from both the ecosystems. Nevertheless, no study has examined how stream configuration within a watershed influences the population of terrestrial predators at the drainage-basin scale. We examined the habitat and abundance relationships of forest insectivorous birds in eight drainage basins in a cool temperate forest of Japan during spring and summer. Each basin has different drainage-basin geomorphology, such as the density and frequency of stream channels. In spring, when terrestrial arthropod prey biomass is limited, insectivorous birds aggregated in habitats closer to streams, where emerging aquatic prey was abundant. Nevertheless, birds ceased to aggregate around streams in summer because terrestrial prey became plentiful. Watershed-scale analyses showed that drainage basins with longer stream channels per unit area sustained higher densities of insectivorous birds. Moreover, such effects of streams on birds continued from spring through summer, even though birds dispersed out of riparian areas in the summer. Although our data are from only a single year, our findings imply that physical modifications of stream channels may reduce populations of forest birds; thus, they emphasize the importance of landscape-based management approaches that consider both stream and forest ecosystems for watershed biodiversity conservation.
Asunto(s)
Aves/fisiología , Conservación de los Recursos Naturales/métodos , Ecosistema , Ambiente , Geografía , Árboles , Animales , Japón , Modelos Estadísticos , Observación , Dinámica Poblacional , Estaciones del AñoRESUMEN
Empirical studies have shown that temporally fluctuating inputs of resource subsidies can indirectly increase or decrease the abundance of in situ resources by affecting generalist consumers that feed on both subsidies and in situ resources. By mathematical modeling, we develop a theoretical framework that can explain these variable consumer-mediated indirect effects. We show that the hierarchy of timescales among fluctuations in the subsidy input rate and consumers' reproductive and aggregative numerical responses predict the signs of the indirect effects. These predictions are consistent with field observations from a variety of natural systems. Our results suggest that the timescale hierarchy of ecological processes is fundamentally important for understanding and predicting indirect effects in nonequilibrium food web dynamics.
Asunto(s)
Cadena Alimentaria , Modelos Biológicos , Simulación por Computador , Factores de TiempoRESUMEN
Since temperature is a key factor affecting photosynthetic and respiration rates, the rates of gross primary production (GPP) and ecosystem respiration (ER) are expected to be lower for rivers at higher latitudes, while the net ecosystem production (NEP) rate likely decrease in rivers at lower latitude due to higher sensitivity of ER to temperature compared with GPP. To examine these possibilities, we estimated the ecosystem metabolism of 30 rivers located from 43.03°N to 32.38°N in Japan during summer using a Bayesian model with hourly changes in dissolved oxygen concentrations. In addition, we examined latitudinal trends of GPP, ER and NEP in a global scale by compiling and analyzing river metabolic data estimated in previous studies. Our analysis showed that both GPP and ER tended to increase with latitude, although these rates were positively related to water temperature in Japanese rivers. Global dataset of GPP and ER also showed increasing trend towards higher latitude. In addition, contrary to our initial expectations, NEP decreased with latitude and most rivers were net heterotrophic at both regional (Japanese rivers) and global scales. These results imply that the latitudinal temperature effect on river metabolism is masked by other factors not examined in this study, such as land use in the watershed, which play pivotal roles in explaining the latitudinal variation of river metabolism.
RESUMEN
Global patterns of biodiversity have emerged for soil microorganisms, plants and animals, and the extraordinary significance of microbial functions in ecosystems is also well established. Virtually unknown, however, are large-scale patterns of microbial diversity in freshwaters, although these aquatic ecosystems are hotspots of biodiversity and biogeochemical processes. Here we report on the first large-scale study of biodiversity of leaf-litter fungi in streams along a latitudinal gradient unravelled by Illumina sequencing. The study is based on fungal communities colonizing standardized plant litter in 19 globally distributed stream locations between 69°N and 44°S. Fungal richness suggests a hump-shaped distribution along the latitudinal gradient. Strikingly, community composition of fungi was more clearly related to thermal preferences than to biogeography. Our results suggest that identifying differences in key environmental drivers, such as temperature, among taxa and ecosystem types is critical to unravel the global patterns of aquatic fungal diversity.
Asunto(s)
Hongos , Microbiota , Ríos/microbiología , Hojas de la Planta/microbiología , Análisis EspacialRESUMEN
Particulate organic phosphorus (P) compounds were examined in ultraoligotrophic Lake Saiko, Japan. A cartridge filter was used to collect sufficient amount of suspended particles for analysis by a two-dimensional NMR (1H-31P heteronuclear multiple bond correlation). 2-Aminoethylphosphonic acid (2-AEP), a phosphonate, was detected in suspended particles in Lake Saiko. The identity of the phosphonate was confirmed by comparison with a commercially available compound. Because 2-AEP is bioavailable, microorganisms can store and use this compound under extremely P-limited conditions. This is the first study to detect 2-AEP in an ultra-oligotrophic environment.
Asunto(s)
Ácido Aminoetilfosfónico/análisis , Lagos/análisis , Contaminantes Químicos del Agua/análisis , Japón , Imagen por Resonancia Magnética/métodos , Organofosfonatos/análisis , Fósforo/análisisRESUMEN
The fluorescence behaviors of potential-sensitive dyes including anionic DiBAC4(3) (denoted by dye A), DiSBAC2(3) (dye B), and zwitterionic di-4-ANEPPS (dye C) were studied in oil-in-water (O/W) emulsions. In this study, the equilibrium Galvani potential difference (ΔOWφeq) of the O/W-emulsion droplets was controlled by changing the ratio of the concentrations of electrolytes added to the O (=1,2-dichloroethane) and W phases. When using an adequate combination of the dyes, i.e., B and C, we could observe that the ratio of their fluorescence peak intensities was changed from 1.08 to 1.38, depending on the change of (ΔOWφeq from 26 to 73 mV. It is desirable to apply this method to study the potential-dependent ion or electron-transfer reactions occurring at vesicles or liposomes, and also to biomembranes.
Asunto(s)
Colorantes Fluorescentes/química , Aceites/química , Electrólitos/química , Emulsiones/química , Potenciales de la Membrana , Tamaño de la Partícula , Electricidad Estática , Agua/químicaRESUMEN
Facultative autotrophs of the genus Sulfuritalea within the class Betaproteobacteria have been predicted to be an important bacterial population in stratified freshwater lakes based on previous PCR-based studies. Here, we designed a new probe specific for the genus Sulfuritalea and performed catalysed reporter deposition-fluorescence in situ hybridisation to enumerate cells of Sulfuritalea species throughout the water column in a stratified freshwater lake. The cells stained with the Sulfuritalea-specific probe were detected in all hypoxic water samples collected in different seasons and years. Their abundance ranged from 1.4 × 104 to 2.1 × 105 cells ml-1 , corresponding to 0.5-5.5% of the total DAPI-stained cells and 2.3-15% of the total bacterial cells. A high abundance of Sulfuritalea species was recorded in hypoxic water samples without nitrate, which is the only known anaerobic electron acceptor for Sulfuritalea. Nitrate-independent anaerobic respiration was further investigated using a single cultured representative of this genus, and its growth via arsenate respiration was experimentally demonstrated. In conclusion, Sulfuritalea species were found to be a major component of the planktonic bacterial community in nitrate-depleted hypoxic water, where arsenate respiration is one of the possible energy metabolisms of Sulfuritalea.
Asunto(s)
Arseniatos/metabolismo , Betaproteobacteria/clasificación , Betaproteobacteria/metabolismo , Agua Dulce/microbiología , Nitratos/metabolismo , Azufre/metabolismo , Microbiología del Agua , Agua/química , Betaproteobacteria/genética , Lagos/microbiología , Consumo de Oxígeno , Filogenia , TemperaturaRESUMEN
The relationship between biodiversity and ecosystem functioning is an important theme in environmental sciences. We propose a new index for configuration of the biomass pyramid in an ecosystem, named integrated trophic position (iTP). The iTP is defined as a sum of trophic positions (i.e. the average number of steps involved in biomass transfer) of all the animals in a food web integrated by their individual biomass. The observed iTP for stream macroinvertebrates ranged from 2.39 to 2.79 and was negatively correlated with the species density and the Shannon-Wiener diversity index of the local community. The results indicate a lower efficiency of biomass transfer in more diverse communities, which may be explained by the variance in edibility hypothesis and/or the trophic omnivory hypothesis. We found a negative effect of biodiversity on ecosystem functioning.
Asunto(s)
Biodiversidad , Cadena Alimentaria , Modelos Teóricos , Ríos , Animales , Biomasa , Invertebrados/fisiologíaRESUMEN
Plant litter represents a major basal resource in streams, where its decomposition is partly regulated by litter traits. Litter-trait variation may determine the latitudinal gradient in decomposition in streams, which is mainly microbial in the tropics and detritivore-mediated at high latitudes. However, this hypothesis remains untested, as we lack information on large-scale trait variation for riparian litter. Variation cannot easily be inferred from existing leaf-trait databases, since nutrient resorption can cause traits of litter and green leaves to diverge. Here we present the first global-scale assessment of riparian litter quality by determining latitudinal variation (spanning 107°) in litter traits (nutrient concentrations; physical and chemical defences) of 151 species from 24 regions and their relationships with environmental factors and phylogeny. We hypothesized that litter quality would increase with latitude (despite variation within regions) and traits would be correlated to produce 'syndromes' resulting from phylogeny and environmental variation. We found lower litter quality and higher nitrogen:phosphorus ratios in the tropics. Traits were linked but showed no phylogenetic signal, suggesting that syndromes were environmentally determined. Poorer litter quality and greater phosphorus limitation towards the equator may restrict detritivore-mediated decomposition, contributing to the predominance of microbial decomposers in tropical streams.
Asunto(s)
Ecosistema , Hojas de la Planta/metabolismo , Plantas/metabolismo , Ríos , Clima Tropical , Nitrógeno/metabolismo , Fósforo/metabolismoRESUMEN
Planktonic sulfur oxidizers are important constituents of ecosystems in stratified water bodies, and contribute to sulfide detoxification. In contrast to marine environments, taxonomic identities of major planktonic sulfur oxidizers in freshwater lakes still remain largely unknown. Bacterioplankton community structure was analyzed in a stratified freshwater lake, Lake Mizugaki in Japan. In the clone libraries of 16S rRNA gene, clones very closely related to a sulfur oxidizer isolated from this lake, Sulfuritalea hydrogenivorans, were detected in deep anoxic water, and occupied up to 12.5% in each library of different water depth. Assemblages of planktonic sulfur oxidizers were specifically analyzed by constructing clone libraries of genes involved in sulfur oxidation, aprA, dsrA, soxB and sqr. In the libraries, clones related to betaproteobacteria were detected with high frequencies, including the close relatives of Sulfuritalea hydrogenivorans.
Asunto(s)
Betaproteobacteria/genética , Agua Dulce/microbiología , Lagos , Plancton/genética , ARN Ribosómico 16S/genética , Azufre/metabolismo , Biodiversidad , ADN Bacteriano/genética , Japón , Microbiología del AguaRESUMEN
Methane oxidation coupled to denitrification is mediated by 'Candidatus Methylomirabilis oxyfera', which belongs to the candidate phylum NC10. The distribution of putative denitrifying methane-oxidizing bacteria related to "M. oxyfera" was investigated in a freshwater lake, Lake Biwa, Japan. In the surface layer of the sediment from a profundal site, a phylotype closely related to "M. oxyfera" was most frequently detected among NC10 bacteria in PCR analysis of the 16S rRNA gene. In the sediment, sequences related to "M. oxyfera" were also detected in a pmoA gene library. The presence of NC10 bacteria was also confirmed by catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH). Denaturing gradient gel electrophoresis (DGGE) and quantitative real-time PCR indicated that the abundance of the "M. oxyfera"-related phylotype was higher in the upper layers of the profundal sediment. The horizontal distribution of the putative methanotrophs in lake sediment was also analyzed by DGGE, which revealed that their occurrence was restricted to deep water areas. These results agreed with those in a previous study of another freshwater lake, and suggested that the upper layer of the profundal sediments is the main habitat for denitrifying methanotrophs.
Asunto(s)
Desnitrificación , Agua Dulce/microbiología , Sedimentos Geológicos/microbiología , Methylococcaceae/clasificación , Methylococcaceae/aislamiento & purificación , Análisis por Conglomerados , ADN Bacteriano/química , ADN Bacteriano/genética , ADN Ribosómico/química , ADN Ribosómico/genética , Electroforesis en Gel de Gradiente Desnaturalizante , Hibridación Fluorescente in Situ , Japón , Methylococcaceae/metabolismo , Datos de Secuencia Molecular , Filogenia , ARN Ribosómico 16S/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Análisis de Secuencia de ADNRESUMEN
Nitrogenous compounds with high delta(15)N values were recently found in human-dominated small rivers in the Lake Biwa area. A detailed survey was performed to determine the distribution and variation of delta(15)N values in nitrogenous compounds in a representative small river (Hebisuna River) that flows into Lake Nishinoko, an inner bay of Lake Biwa. A high delta(15)N value was detected in the lower reaches of the river and the inner bay, most likely due to denitrification. These results strongly suggest that denitrification in small river systems such as the Hebisuna watershed has contributed to (15)N enrichment in the Lake Biwa ecosystem during the past 40 years. We also observed a clear, stepwise, positive correlation between population density and delta(15)N values for particulate organic matter or sediments. These results demonstrate that delta(15)N (POM) and delta(15)N (sediment) are helpful indicators for assessing nitrogen loading from domestic sewage. Moreover, they will aid in the development of new concepts in the environmental capacity of river ecosystems and its relationship to redox conditions. Finally, our data suggest that a population density of 100-200 persons per km(2) is the upper limit for a watershed in which only simple conventional sewage treatment is in effect.
Asunto(s)
Ecosistema , Nitrógeno/análisis , Ríos/química , Contaminantes Químicos del Agua/análisis , Cloruros/análisis , Monitoreo del Ambiente , Humanos , Japón , Nitrógeno/química , Isótopos de Nitrógeno/análisis , Densidad de Población , Contaminantes Químicos del Agua/química , Abastecimiento de AguaRESUMEN
A novel method for radioisotope-free photoaffinity labeling was developed, in which a bifunctional ligand is connected to a target protein by activation of a photoreactive group, such as an aromatic azido or 3-trifluoromethyl-3H-diazirin-3-yl group, and identification of the ligated product is achieved by anchoring of a detectable tag through the Staudinger-Bertozzi reaction with an alkyl azido moiety that survives photolysis. The chemical ground of this method was confirmed using model compounds with the bifunctional group under photoirradiation in the presence of trapping agents for reactive intermediates. The utility of the method has been demonstrated by specific labeling of the catalytic portion of human HMG-CoA reductase.