Seasonal Response of Stream Biofilm Communities to Dissolved Organic Matter and Nutrient Enrichments

Dissolved organic matter (DOM) and inorganic nutrients may affect microbial communities in streams, but little is known about the impact of these factors on specific taxa within bacterial assemblages in biofilms. In this study, nutrient diffusing artificial substrates were used to examine bacterial responses to DOM (i.e., glucose, leaf leachate, and algal exudates) and inorganic nutrients (nitrate and phosphate singly and in combination). Artificial substrates were deployed for five seasons, from summer 2002 to summer 2003, in a northeastern Ohio stream. Differences were observed in the responses of bacterial taxa examined to various DOM and inorganic nutrient treatments, and the response patterns varied seasonally, indicating that resources that limit the bacterial communities change over time. Overall, the greatest responses were to labile, low-molecular-weight DOM (i.e., glucose) at times when chlorophyll a concentrations were low due to scouring during significant storm events. Different types of DOM and inorganic nutrients induced various responses among bacterial taxa in the biofilms examined, and these responses would not have been apparent if they were examined at the community level or if seasonal changes were not taken into account.     

Impacts of Labile Organic Carbon Concentration on Organic and Inorganic Nitrogen Utilization by a Stream Biofilm Bacterial Community

In aquatic ecosystems, carbon (C) availability strongly influences nitrogen (N) dynamics. One manifestation of this linkage is the importance in the dissolved organic matter (DOM) pool of dissolved organic nitrogen (DON), which can serve as both a C and an N source, yet our knowledge of how specific properties of DOM influence N dynamics are limited. To empirically examine the impact of labile DOM on the responses of bacteria to DON and dissolved inorganic nitrogen (DIN), bacterial abundance and community composition were examined in controlled laboratory microcosms subjected to various combinations of dissolved organic carbon (DOC), DON, and DIN treatments. Bacterial communities that had colonized glass beads incubated in a stream were treated with various glucose concentrations and combinations of inorganic and organic N (derived from algal exudate, bacterial protein, and humic matter). The results revealed a strong influence of C availability on bacterial utilization of DON and DIN, with preferential uptake of DON under low C concentrations. Bacterial DON uptake was affected by the concentration and by its chemical nature (labile versus recalcitrant). Labile organic N sources (algal exudate and bacterial protein) were utilized equally well as DIN as an N source, but this was not the case for the recalcitrant humic matter DON treatment. Clear differences in bacterial community composition among treatments were observed based on terminal restriction fragment length polymorphisms (T-RFLP) of 16S rRNA genes. C, DIN, and DON treatments likely drove changes in bacterial community composition that in turn affected the rates of DON and DIN utilization under various C concentrations.     

Response of Biofilm Bacteria to Dissolved Organic Matter from Decomposing Maple Leaves

Stream bacteria play an important role in the utilization of dissolved organic matter (DOM) leached from leaves, and in transfer of this DOM to other trophic levels. Leaf leachate is a mixture of labile, recalcitrant, and inhibitory compounds, and bacterial communities vary in their ability to utilize leachate. The purpose of this study was to determine the effects of DOM from sugar maple leaves on bacterial populations in biofilms on decomposing leaf surfaces. Populations of Acinetobacter calcoaceticus, Burkholderia cepacia, and Pseudomonas putida were enumerated on decomposing maple leaves in a northeast Ohio stream using fluorescence in situ hybridization. Additionally, artificial substrata consisting of PVC-end caps filled with agar supplemented with leaf leachate and covered with cellulose filters were used to determine bacterial response to leachate from leaves at different stages of decomposition. Population sizes of bacterial species exhibited different responses. Leachate did not affect A. calcoaceticus. B. cepacia was tolerant of phenolic compounds released from leaves and the population size increased when DOM concentrations were greatest. In contrast, P. putida was inhibited by phenolic components of leachate when total DOM concentrations were greatest. Differences in response of the bacterial species to components of leaf leachate indicate the complexity of microbial population dynamics and interactions with DOM. Differences among species in response to DOM have the potential to influence transport and retention of organic matter in stream ecosystems.     

Rehabilitation of Stream Ecosystem Functions through the Reintroduction of Coarse Particulate Organic Matter

In streams, coarse particulate organic matter (CPOM) acts as a substrate for microbial activity, which promotes nutrient retention. However, in urban areas, increased peak flows within streams lead to decreased retention of CPOM. The aim of this study was to investigate whether the reintroduction of CPOM, in the form of leaf litter, into a degraded urban stream would increase biofilm activity and phosphorus retention, two ecosystem functions that reflect the integrity of the ecosystem. Stream metabolism and nutrient retention were assessed in treated (T) and control (C) channels of the Torrens River Catchment, South Australia, before and after CPOM addition. Gross primary production and community respiration (CR) were measured as oxygen production and consumption within benthic chambers. Phosphorus retention was measured through a series of short-term filterable reactive phosphorus (FRP) addition experiments. Before CPOM addition, there were no differences in CR, but C retained 6.8% more FRP than T. After CPOM addition, CR was greater in T than in C (572 and 276 mg O₂·m⁻²·day⁻¹, respectively), and T retained 7.7% more FRP than C. The increase in FRP retention in T compared to C was attributed to phosphorus limitation of the CPOM and increased demand for phosphorus of the attached microbial heterotrophic community. The reintroduction of CPOM into degraded streams will be an important step in the restoration of stream metabolism and nutrient retention. Maintenance of CPOM may be achieved through restoration of riparian vegetation, a reduction in the increased peak flows, and rehabilitation of stream morphology.     

Labile and Recalcitrant Organic Matter Utilization by River Biofilm Under Increasing Water Temperature

Microbial biofilms in rivers contribute to the decomposition of the available organic matter which typically shows changes in composition and bioavailability due to their origin, seasonality, and watershed characteristics. In the context of global warming, enhanced biofilm organic matter decomposition would be expected but this effect could be specific when either a labile or a recalcitrant organic matter source would be available. A laboratory experiment was performed to mimic the effect of the predicted increase in river water temperature (+4?°C above an ambient temperature) on the microbial biofilm under differential organic matter sources. The biofilm microbial community responded to higher water temperature by increasing bacterial cell number, respiratory activity (electron transport system) and microbial extracellular enzymes (extracellular enzyme activity). At higher temperature, the phenol oxidase enzyme explained a large fraction of respiratory activity variation suggesting an enhanced microbial use of degradation products from humic substances. The decomposition of hemicellulose (β-xylosidase activity) seemed to be also favored by warmer conditions. However, at ambient temperature, the enzymes highly responsible for respiration activity variation were β-glucosidase and leu-aminopeptidase, suggesting an enhanced microbial use of polysaccharides and peptides degradation products. The addition of labile dissolved organic carbon (DOC; dipeptide plus cellobiose) caused a further augmentation of heterotrophic biomass and respiratory activity. The changes in the fluorescence index and the ratio Abs(250)/total DOC indicated that higher temperature accelerated the rates of DOC degradation. The experiment showed that the more bioavailable organic matter was rapidly cycled irrespective of higher temperature while degradation of recalcitrant substances was enhanced by warming. Thus, pulses of carbon at higher water temperature might have consequences for DOC processing.     

Seasonal Variability of Particulate Organic Matter in a Mountain Stream in Central Spain

The aim of this paper was to study the influence of environmental characteristics of the Mediterranean climate on seasonal variability of particulate organic matter abundance in a mountain stream. Coarse and fine fractions of both suspended and benthic particulate organic matter were determined on 14 occasions between February 1998 and November 1999 in a second‐order Mediterranean stream in Central Spain (Arroyo Mediano). Temporal variability of suspended organic matter followed a seasonal pattern, attributed to litter‐fall inputs, instream processing, and the hydrological regime. Suspended organic matter (SOM) and its seasonal variability fall well within the range reported for streams in temperate non‐Mediterranean deciduous forest. However, we found no seasonal trend in benthic organic matter (BOM) storage, and it seems that the amount of BOM remained fairly constant throughout the year. Reach retention (evaluated as the ratio between BOM and SOM per m²) was higher in summer during reduced stream flow, mainly due to coarse particulate organic matter storage. These observations do not differ from those reported for other headwater streams in temperate forested biomes, from which we conclude that there was no evidence of a Mediterranean influence on particulate organic matter dynamics in the Mediano stream, nor probably in other headwater Mediterranean streams. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Physical Heterogeneity Increases Biofilm Resource Use and Its Molecular Diversity in Stream Mesocosms

Background

Evidence increasingly shows that stream ecosystems greatly contribute to global carbon fluxes. This involves a tight coupling between biofilms, the dominant form of microbial life in streams, and dissolved organic carbon (DOC), a very significant pool of organic carbon on Earth. Yet, the interactions between microbial biodiversity and the molecular diversity of resource use are poorly understood.

Methodology/Principal Findings

Using six 40-m-long streamside flumes, we created a gradient of streambed landscapes with increasing spatial flow heterogeneity to assess how physical heterogeneity, inherent to streams, affects biofilm diversity and DOC use. We determined bacterial biodiversity in all six landscapes using 16S-rRNA fingerprinting and measured carbon uptake from glucose and DOC experimentally injected to all six flumes. The diversity of DOC molecules removed from the water was determined from ultrahigh-resolution Fourier Transform Ion Cyclotron Resonance mass spectrometry (FTICR-MS). Bacterial beta diversity, glucose and DOC uptake, and the molecular diversity of DOC use all increased with increasing flow heterogeneity. Causal modeling and path analyses of the experimental data revealed that the uptake of glucose was largely driven by physical processes related to flow heterogeneity, whereas biodiversity effects, such as complementarity, most likely contributed to the enhanced uptake of putatively recalcitrant DOC compounds in the streambeds with higher flow heterogeneity.

Conclusions/Significance

Our results suggest biophysical mechanisms, including hydrodynamics and microbial complementarity effects, through which physical heterogeneity induces changes of resource use and carbon fluxes in streams. These findings highlight the importance of fine-scale streambed heterogeneity for microbial biodiversity and ecosystem functioning in streams, where homogenization and loss of habitats increasingly reduce biodiversity.     

Intra-Annual Variation in Benthic Organic Matter in A Saline,Semi-Arid Stream of Southeast Spain (Chicamo Stream)

Hydrobiologia - During 1994 and 1998–1999, temporal changes in the benthic organic matter (BOM) and its fractions (CBOM = coarse; FBOM = fine; UBOM = ultrafine) were studied in a 354-m reach...     

Coarse Particulate Organic Matter Distribution in the Pools and Riffles of a Second-order Stream

Coarse particulate organic matter distribution was investigated in a 270-m interval of a 2nd-order forest stream, the Yanase River. The dominant tree type was Keyaki (Zelkova serrata). CPOM sampling was conducted, and the sampled CPOM was sorted into leaves and branches, and water depth and current velocity were measured along with stone width, stone height and distance between the stones in the riffles. The collected CPOM was categorized by their accumulation type: LSS, SLP, SLPi, SLPo and DD. LSS was leaf packs at the leading edge of the stones, SLP was the sinking leaf packs in the pools, SLPi was the sinking leaf packs at the inner side of the stream bend in the pools, while SLPo was the sinking leaf packs at the outer side of the stream bend, and finally, DD was the leaf packs in the debris dams. The accumulated CPOM amounts at each leaf pack type were correlated with the measured physical stream variables. From the results, CPOM accumulation in riffles is controlled by stones projecting above the water surface and by their arrangements. In pools, CPOM accumulation occurs at high stream flow where the pools provide low velocities and a thick boundary layer of relatively quiescent flow. At stream meandering points, CPOM accumulation occurs by production of a secondary flow. Finally, CPOM accumulation in debris dams is important where they occur frequently. LSS was the largest in CPOM amount, and the stones in the riffles were the most retentive structures. On the other hand, SLP and SLPo were the least CPOM amounts, and the pools in the mainstream and at the outer side of the stream bend were the least retentive stream morphologies.     

Algal Exudates and Stream Organic Matter Influence the Structure and Function of Denitrifying Bacterial Communities

Within aquatic ecosystems, periphytic biofilms can be hot spots of denitrification, and previous work has suggested that algal taxa within periphyton can influence the species composition and activity of resident denitrifying bacteria. This study tested the hypothesis that algal species composition within biofilms influences the structure and function of associated denitrifying bacterial communities through the composition of organic exudates. A mixed population of bacteria was incubated with organic carbon isolated from one of seven algal species or from one of two streams that differed in anthropogenic inputs. Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) revealed differences in the organic composition of algal exudates and stream waters, which, in turn, selected for distinct bacterial communities. Organic carbon source had a significant effect on potential denitrification rates (DNP) of the communities, with organics isolated from a stream with high anthropogenic inputs resulting in a bacterial community with the highest DNP. There was no correlation between DNP and numbers of denitrifiers (based on nirS copy numbers), but there was a strong relationship between the species composition of denitrifier communities (as indicated by tag pyrosequencing of nosZ genes) and DNP. Specifically, the relative abundance of Pseudomonas stutzeri-like nosZ sequences across treatments correlated significantly with DNP, and bacterial communities incubated with organic carbon from the stream with high anthropogenic inputs had the highest relative abundance of P. stutzeri-like nosZ sequences. These results demonstrate a significant relationship between bacterial community composition and function and provide evidence of the potential impacts of anthropogenic inputs on the structure and function of stream microbial communities.     

Effects of Duration,Frequency, and Severity of the Non-flow Period on Stream Biofilm Metabolism

Ecosystems - Temporary streams make up the majority of river networks in many regions around the world. Although they are known to have non-flow periods, it is uncertain in what ways the temporal...     

Effects of Organic Matter on Solubilities and Crystal Form of Carbonates

The results of a study of the role of organic compounds in theformation of carlxmate crystals in marine biological systemsare reported. In an increasing concentration of certain organiccompounds which complex calcium ions, the proportion of aragonitedecreases and that of calcite increases. In increasing concentrationsof magnesium ions the proportion of aragonite increases andthat of calcite and vaterite decreases. When the influence oforganic compounds is greater or smaller than that of magnesiumions, only calcite or only aragonite is formed, respectively.Organic compounds forming a strong complex with calcium ionscause the formation of magnesium-rich calcite, and with an increasein temperature and the concentration of magnesium ions, themagnesium carbonate content of precipitated magnesian calciteincreases. When the influence of organic compounds is almostequivalent to that of magnesium ions, in increasing or decreasingtemperatures, the proportion of calcite decreases or increases,respectively, and the proportion of aragonite increases or decreases,respectively. The concentration of magnesium ions in the bodyfluids of marine calcareous organisms seems to differ littlefrom that of other organisms, and seems to be similar to thatof sea water. Only the presence of certain organic compoundsbrings about the formation of the carbonate crystals observedin marine biological systems. The very important role of organicmatter in the formation of crystals found in skeletal carbonatesis emphasized.     

Life History of Lepidostoma hirtum in an Iberian Stream and its Role in Organic Matter Processing

The goal of this research was to determine the role of Lepidostoma hirtum Fabricius 1775 in the fragmentation of allochtonous organic material, in a segment of a mountain river in central Portugal. For this purpose, we measured leaf fragmentation and growth rates at four temperatures (9, 12, 15 and 18 °C) and four leaf types (alder, Alnus glutinosa L.; oak, Quercus andegavensis Hy; poplar, Populus × canadensis Moench; and chestnut, Castanea sativa Mill.). Growth rates ranged from 0.012 to 0.049 mg AFDW day⁻¹ with no significant effect of temperature and leaf type. Fragmentation/consumption rates were significantly higher for alder (1.62 mg animal⁻¹ day⁻¹) than for other leaf types, and significantly lower at 9 °C (0.70 mg animal⁻¹ day⁻¹) than at any other temperature (1.12 mg animal⁻¹ day⁻¹). In the studied stream, L. hirtum larvae had a univoltine life history, with an asynchronous development. Secondary production of L. hirtum ranged from 53.95 mg m⁻² year⁻¹ (pools) to 63.12 mg m⁻² year⁻¹ (riffles). Annual P/B ratios differ between habitats: they were 4.01 year⁻¹ for pools and 4.49 year⁻¹ for riffles. Considering the average density of this species in the study river and their consumption rates, this species has the potential to fragment 8.6 times the mean annual standing stock of organic matter, in the study location.     

Environmental Dissolved Organic Matter Governs Biofilm Formation and Subsequent Linuron Degradation Activity of a Linuron-Degrading Bacterial Consortium

It was examined whether biofilm growth on dissolved organic matter (DOM) of a three-species consortium whose members synergistically degrade the phenylurea herbicide linuron affected the consortium''s integrity and subsequent linuron-degrading functionality. Citrate as a model DOM and three environmental DOM (eDOM) formulations of different quality were used. Biofilms developed with all DOM formulations, and the three species were retained in the biofilm. However, biofilm biomass, species composition, architecture, and colocalization of member strains depended on DOM and its biodegradability. To assess the linuron-degrading functionality, biofilms were subsequently irrigated with linuron at 10 mg liter⁻¹ or 100 μg liter⁻¹. Instant linuron degradation, the time needed to attain maximal linuron degradation, and hence the total amount of linuron removed depended on both the DOM used for growth and the linuron concentration. At 10 mg liter⁻¹, the final linuron degradation efficiency was as high as previously observed without DOM except for biofilms fed with humic acids which did not degrade linuron. At 100 μg liter⁻¹ linuron, DOM-grown biofilms degraded linuron less efficiently than biofilms receiving 10 mg liter⁻¹ linuron. The amount of linuron removed was more correlated with biofilm species composition than with biomass or structure. Based on visual observations, colocalization of consortium members in biofilms after the DOM feed appears essential for instant linuron-degrading activity and might explain the differences in overall linuron degradation. The data show that DOM quality determines biofilm structure and composition of the pesticide-degrading consortium in periods with DOM as the main carbon source and can affect subsequent pesticide-degrading activity, especially at micropollutant concentrations.     

Effects of Watershed History on Dissolved Organic Matter Characteristics in Headwater Streams

Dissolved organic matter (DOM) is recognized as a major component in the global carbon cycle and is an important driver in aquatic ecosystem function. Climate, land use, and forest cover changes all impact stream DOM and alter biogeochemical cycles in terrestrial environments. We determined the temporal variation in DOM quantity and quality in headwater streams at a reference watershed (REF), a watershed clear-cut 30 years ago (CC), and a watershed converted to a white pine plantation 50 years ago (WP) at the US Forest Service, Coweeta Hydrologic Laboratory, in the Nantahala Mountains of western North Carolina, USA. Average stream dissolved organic carbon (DOC) concentrations in CC or WP were 60 and 80% of those in REF, respectively. Stream DOM composition showed that the difference was mainly due to changes in humic-like components in chromophoric DOM. In addition, excitation–emission matrix fluorescence data with parallel factor analysis indicate that although the concentration of protein-like components did not differ significantly among watersheds, their relative abundance showed an enrichment in CC and WP compared to REF. The ratio of humic acid-type to fulvic acid-type components was highest and lowest at REF and WP, respectively. Our data suggest that forest ecosystem disturbance history affects the DOM quantity and quality in headwater streams over decades as a result of changes in watershed soil organic matter characteristics due to differences in organic matter inputs.     

Effect of Native Vegetation Loss on Stream Ecosystem Processes: Dissolved Organic Matter Composition and Export in Agricultural Landscapes

Stream and river ecosystems are dependent on energetic inputs from their watersheds and thus shifts in land use from forest cover to agriculture will affect stream community composition and function. The disruption of forest-aquatic linkages alters the organic matter resources in agricultural streams. Dissolved organic matter (DOM) is the dominant form of organic matter in aquatic ecosystems, and a microbial energy source that is important for stream respiration. The concentrations and characteristics of DOM are regulated by both terrestrial (for example, terrestrial organic matter supply) and in-stream processes (for example, microbial respiration and periphyton production) that are influenced by land management. The effects of watershed land use and topographic, soil and climatic variables on DOM quantity (dissolved organic carbon concentration and load), source (terrestrial or in-stream) and quality (composition and lability) were measured in 14 streams across an agricultural land-use gradient. DOC concentration was positively correlated with watershed pasture cover and negatively correlated with watershed relief. No watershed variables were important correlates of DOC load. Stream DOM was primarily of terrestrial origin, but DOM in agricultural streams had a greater proportion of sources from in-stream sources. This may be due to reduced connection with riparian vegetation and increased in-stream primary production. We suggest that maintaining watershed tree cover greater than 52% and ensuring less than 10% of the length of riparian corridor is cleared for pasture could minimize changes to DOM composition. This is important to avoid flow-on effects for stream ecosystem processes that are mediated by DOM. Long-term DOM monitoring will be valuable for assessing the functional impacts of land-use change.     

土壤有机质和外源有机物对甲烷产生的影响

对土壤有机质含量及组分、外源有机物和根系分泌对甲烷产生的影响作了综述。土壤产甲烷量和甲烷排放量随有机质含量增加而提高,与土壤中易矿化有机碳或沸水浸提有机碳含量呈显著相关。外源有机碳加入促进了土壤排放甲,刺激效果与外源有机碳的用量和组成有关。还原力强的有机物如纤维素和半纤维素较还原力弱的有机物如类脂和多糖能够产生更多的甲烷。甲醇、甲基化氨基酸等无其它微生物竞争利用的有机物能被产甲烷菌更多地转化成甲烷。植物根系分泌物也促进甲烷的产生,促进作用大小与植物种类及分泌物的数量和质量有关。外源有机物通过3种方式促进土壤甲烷产生;提高土壤的甲烷底物供应量,降低土壤氧化还原电位,刺激土壤原有有机碳的转化。     

遮荫对雪茄外包皮烟生长和光合特性的影响

采用全光照(Lck)与遮荫处理———透光率为71%(L1)、63%(L2)和22%(L3),对雪茄外包皮烟生长发育及其光合特性进行了研究.结果显示:(1)随着透光率的降低,烟株茎变细,叶片变薄;株高和叶面积各处理均先增加后降低,且在L2遮荫条件下株高和叶面积显著高于其它处理,分别达最大值(32.5 cm,47 620 cm2);根系干重显著降低,总干重先增加至透光率为63%时达最大值,当透光率降至22%时又显著降低;净光合效率(Pn)呈先增加后降低趋势,且在透光率为71%的遮荫条件下达最大值;(2)遮荫处理可显著提高雪茄外包皮烟叶绿素含量和Fv/F0值,使ΦpsⅡ、Fv/Fm和QP值增大、QN和Chl a/b的值降低.研究表明,透光率为63%的遮荫处理下雪茄外包皮烟植株地上部分生长最好.     

Flow is more Important than Temperature in Driving Patterns of Organic Matter Storage and Stoichiometry in Stream Ecosystems

Ecosystems - Understanding the connections between biological communities and elemental cycles is increasingly important given that alterations to both are occurring on a global scale. Biological...     

Growth of Ferrobacillus ferrooxidans on Organic Matter

Following a brief adaptation period to glucose, Ferrobacillus ferrooxidans was grown on glucose, mannitol, several other sugars, and a few amino acids in the absence of an oxidizable iron source. Prolonged growth on an organic substrate free from iron rendered the organism obligately organotrophic. The growth rate of the bacterium was greater in heterotrophic culture; the doubling time was approximately 4.5 hr on glucose. The bacterium retained its acidophilic properties during adaptation and growth on glucose and would not grow in neutral or slightly alkaline media. Addition of p-aminobenzoic acid was necessary for abundant growth of the cells on glucose. Of the eight strains of Fe(++)-oxidizing bacteria studied, only two strains grew on glucose in a nondialyzed system. The results of manometric studies are discussed with regard to metabolic efficiency of organic matter in this organism.