Limitation of bacterial growth by dissolved organic matter and iron in the Southern ocean

The importance of resource limitation in controlling bacterial growth in the high-nutrient, low-chlorophyll (HNLC) region of the Southern Ocean was experimentally determined during February and March 1998. Organic- and inorganic-nutrient enrichment experiments were performed between 42 degrees S and 55 degrees S along 141 degrees E. Bacterial abundance, mean cell volume, and [(3)H]thymidine and [(3)H]leucine incorporation were measured during 4- to 5-day incubations. Bacterial biomass, production, and rates of growth all responded to organic enrichments in three of the four experiments. These results indicate that bacterial growth was constrained primarily by the availability of dissolved organic matter. Bacterial growth in the subtropical front, subantarctic zone, and subantarctic front responded most favorably to additions of dissolved free amino acids or glucose plus ammonium. Bacterial growth in these regions may be limited by input of both organic matter and reduced nitrogen. Unlike similar experimental results in other HNLC regions (subarctic and equatorial Pacific), growth stimulation of bacteria in the Southern Ocean resulted in significant biomass accumulation, apparently by stimulating bacterial growth in excess of removal processes. Bacterial growth was relatively unchanged by additions of iron alone; however, additions of glucose plus iron resulted in substantial increases in rates of bacterial growth and biomass accumulation. These results imply that bacterial growth efficiency and nitrogen utilization may be partly constrained by iron availability in the HNLC Southern Ocean.     

Microbial biomass and utilization of dissolved organic matter in the okefenokee swamp ecosystem

The Okefenokee Swamp exhibited levels of microbial biomass and aerobic glucose uptake comparable to those of other organically rich, detritus-based aquatic ecosystems. In contrast to other peat-accumulating systems, this acidic (pH 3.7), low-nutrient environment does not show diminished water column or surface sediment microbial biomass or heterotrophic activity. The total particular ATP varied between 0.03 and 6.6 mug liter (mean, 1.6 mug liter) in water and between 1 and 28 mug g (dry weight) (mean, 10.0 mug g [dry weight] in sediments. The turnover times for dissolved d-glucose were 1.26 to 701.25 h (mean, 110.25 h) in aerobic waters and 2.4 to 72 min (mean, 10.2 min) in aerobic surface sediments. Water column bacterial secondary production, measured as the incorporation of [H]thymidine into cold-trichloroacetic acid-insoluble material, ranged from 0.06 to 1.67 nmol liter day (mean, 0.45 nmol liter day). The kinetics of d-glucose uptake by water column microflora are multiphasic and suggest the presence of a diverse microbial population capable of using labile substrates at nanomolar concentrations and at substantial rates. The presence of a large and active aerobic microbial community in the Okefenokee Swamp is indicative of an important role for microbes in swamp geochemistry and strongly suggests the existence of a detritus-based food web.     

Benthic organic matter dynamics in Texas prairie streams

Concentrations of benthic particulate organic matter (POM) in six Texas prairie streams (2nd–4th order, intermittent and perennial) were monitored over a 20 month period to determine temporal and spatial dynamics. Benthic POM mass was highly variable, having coefficients of variation (CV) in excess of 300%. Benthic POM mass in all streams was similar with the exception of the 4th order intermittent stream which had significantly higher concentrations. Benthic POM at all sites was dominated by coarse POM (CPOM), followed by fine POM (FPOM), ultrafine POM (UPOM), and medium POM (MPOM). The dominance by CPOM is especially noteworthy in the 4th order intermittent stream where it accounted for 83% of the annual POM mass. Seasonally, benthic POM was highest in summer and lowest in the fall.     

水溶性有机质对土壤吸附菲的影响

研究了来源于稻草腐熟物的外源水溶性有机质(DOM)和土壤本身固有的内源DOM对有机碳含量不同的3种土壤吸附菲的影响.结果表明,不同处理土壤对菲的吸附曲线均为线性,其吸附系数(K_d)与土壤有机碳含量(f_oc)正相关.去除内源DOM后,黄棕壤、红粘田和黑土吸附菲的K_d值增加了7.08%～21.4%,增加量(ΔK_d)和增加幅度与f_oc正相关,表明土壤中存在的内源DOM抑制土壤对菲的吸附.而外源DOM对土壤吸附菲的影响与其浓度密切相关.在供试浓度范围(0～106 mg DOC·L^-1)内,红粘田吸附菲的K_d值随加入外源DOM浓度的提高先增大后减小.外源DOM浓度为28 mg DOC·L^-1时,红粘田吸附菲的K_d值增加了19.5%;而当外源DOM浓度≥52 mg DOC·L^-1时,则明显抑制菲的吸附.内源和外源DOM对土壤吸附菲的影响,主要与DOM和菲在溶液中的结合作用、在土壤中的累积吸附效应等有关.     

水溶性有机物对黑麦草吸收铜的影响

采用水培试验,研究蚓粪及蚯蚓培养载体牛粪中水溶性有机物(DOM)对不同Cu2+浓度下(0、5、10 mg·L-1)黑麦草吸收Cu2+的影响.结果表明:随着Cu2+浓度的增加,黑麦草地上部、根干质量,以及根系的长度、表面积、体积和根尖数均逐渐下降;DOM显著增加了Cu2+处理下黑麦草地上部及根系生物量,促进了其根系的长度、表面积、体积和根尖数的增长.DOM降低了黑麦草地下部Cu2+浓度,促进了Cu2+从地下部向地上部的运输,显著增加了地上部Cu2+积累量.蚓粪DOM对黑麦草的影响优于牛粪DOM,并且供试高浓度DOM效果优 于低浓度.     

Benthic bacterial biomass and production in the Hudson River estuary

Bacterial biomass, production, and turnover were determined for two freshwater marsh sites and a site in the main river channel along the tidally influenced Hudson River. The incorporation of [methyl-³H]thymidine into DNA was used to estimate the growth rate of surface and anaerobic bacteria. Bacterial production at marsh sites was similar to, and in some cases considerably higher than, production estimates reported for other aquatic wetland and marine sediment habitats. Production averaged 1.8–2.8 mg C·m^–2·hour^–1 in marsh sediments. Anaerobic bacteria in marsh sediment incorporated significant amounts of [methyl-³H]thymidine into DNA. Despite differences in dominant vegetation and tidal regime, bacterial biomass was similar (1×10³±0.08 mg C·m^–2) inTrapa, Typha, andNuphar aquatic macrophyte communities. Bacterial abundance and productivity were lower in sandy sediments associated withScirpus communities along the Hudson River (0.2×10³±0.05 mg C·m^–2 and 0.3±0.23 mg C·m^–2·hour^–1, respectively).     

Urban infrastructure influences dissolved organic matter quality and bacterial metabolism in an urban stream network

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Influence of cladoceran grazing activity on dissolved organic matter, enzymatic hydrolysis and bacterial growth

To assess the influence of grazing by cladocerans on dissolvedorganic matter (DOM), glycolytic and proteolytic activitiesand bacterial growth were measured by in situ incubation oflake water from the epilimnion of an oligotrophic reservoirin three different treatments: in absence of zooplankton, andin presence of zooplankton (natural abundance and concentratedfour-fold). These experiments were conducted at two periodsin the succession of plankton populations (May and June 1998),that differed in the quality of the prey ingested (Eudorinasp. compared to Cryptomonas sp. and Rhodomonas sp.) and theirgrazing intensity (31.8 ± 2.2 µg C l^–1 day^–1compared to 10.2 ± 0.5 µg C l^–1 day^–1).A systematic increase in bacterial biomass was measured in thetreatments containing the highest zooplankton concentrations.The DOM concentrations produced in situ showed few significantdifferences between the three treatments, but the assimilationof DOM was higher in the presence of zooplankton than in theirabsence. These results show that the influence of cladoceranson the DOM was more of a qualitative than a quantitative nature.The protein compounds derived from the grazing activities ofmetazoans seem to be a major nutrient source for growth forbacteria (r = 0.81, P <0.05). In this study, the highesthydrolytic activities were recorded in the presence of highconcentrations of metazoan zooplankton. However, the processesthat regulated these activities differed between the two experimentaldates (repression compared to enzyme stimulation). Grazing activitiescould lead to an increase in phytoplanktonic excretion duringthe growth phase, and therefore the production of low molecularweight compounds that are easily assimilated by the bacterialplankton.     

Interactive effects of solar radiation and dissolved organic matter on bacterial activity and community structure

We studied the interactive effects of dissolved organic matter (DOM) and solar radiation on the activity and community structure of bacteria from an alpine lake. Activity was assessed both at the community level as leucine incorporation rates and at the single-cell level by microautoradiography. Fluorescent in situ hybridization and signal amplification by catalysed reporter deposition (CARD-FISH) was used to track changes in the bacterial community composition. Bacteria-free filtrates of different DOM sources (lake, algae or soil) were incubated either in the dark or exposed to solar radiation. Afterwards, the natural bacterial assemblage was inoculated and the cultures incubated in the dark for 24-48 h. Bacterial activity was enhanced in the first 24 h in the soil and algal DOM amendments kept in the dark. After 48 h, the enhancement effect was greatly reduced. The initial bacterial community was dominated by Betaproteobacteria followed by Actinobacteria. The relative abundance (expressed as a percentage of DAPI-stained cells) of Betaproteobacteria increased first in dark incubated DOM amendments, but after 48 h no significant differences were detected among treatments. In contrast, the relative abundance of Actinobacteria increased in pre-irradiated DOM treatments. Although Betaproteobacteria dominated at the end of the experiment, the relative abundance of their R-BT subgroup differed among treatments. Changes in bacterial community activity were significantly correlated with those of the relative abundance and activity of Betaproteobacteria, whereas the contribution of Actinobacteria to the bulk activity was very modest. Our results indicate a negative effect of DOM photoalteration on the bulk bacterial activity. The magnitude of this effect was time-dependent and related to rapid changes in the bacterial assemblage composition.     

Dynamics and characterization of refractory dissolved organic matter produced by a pure bacterial culture in an experimental predator-prey system

We studied the effects of a bacterium (Pseudomonas chlororaphis) and a bactivorous protozoan (Uronema sp.) on transformations of labile dissolved organic carbon (DOC). In 36-day time series experiments, bacteria were grown on glucose both with and without protozoa. We measured bulk organic carbon pools and used electrospray ionization mass spectrometry to characterize dissolved organic matter on a molecular level. Bacteria rapidly utilized glucose, depleting it to nondetectable levels and producing new DOC compounds of higher molecular weight within 2 days. Some of these new compounds, representing 3 to 5% of the initial glucose-C, were refractory and persisted for over a month. Other new compounds were produced and subsequently used by bacteria during the lag and exponential growth phases, pointing to a dynamic cycling of organic compounds. Grazers caused a temporary spike in the DOC concentration consisting of labile compounds subsequently utilized by the bacteria. Grazing did not increase the complexity of the DOC pool already established by the bacteria but did continually decrease the particulate organic carbon pool and expedited the conversion of glucose-C to CO2. After 36 days, 29% of initial glucose-C remained in pure bacteria cultures, while only 6% remained in cultures where a grazer was present. In this study the bacteria were the primary shapers of the complex DOC continuum, suggesting higher trophic levels possibly have less of an impact on the qualitative composition of DOC than previously assumed.     

Net production and consumption of fluorescent colored dissolved organic matter by natural bacterial assemblages growing on marine phytoplankton exudates

An understanding of the distribution of colored dissolved organic matter (CDOM) in the oceans and its role in the global carbon cycle requires a better knowledge of the colored materials produced and consumed by marine phytoplankton and bacteria. In this work, we examined the net uptake and release of CDOM by a natural bacterial community growing on DOM derived from four phytoplankton species cultured under axenic conditions. Fluorescent humic-like substances exuded by phytoplankton (excitation/emission [Ex/Em] wavelength, 310 nm/392 nm; Coble's peak M) were utilized by bacteria in different proportions depending on the phytoplankton species of origin. Furthermore, bacteria produced humic-like substances that fluoresce at an Ex/Em wavelength of 340 nm/440 nm (Coble's peak C). Differences were also observed in the Ex/Em wavelengths of the protein-like materials (Coble's peak T) produced by phytoplankton and bacteria. The induced fluorescent emission of CDOM produced by prokaryotes was an order of magnitude higher than that of CDOM produced by eukaryotes. We have also examined the final compositions of the bacterial communities growing on the exudates, which differed markedly depending on the phytoplankton species of origin. Alteromonas and Roseobacter were dominant during all the incubations on Chaetoceros sp. and Prorocentrum minimum exudates, respectively. Alteromonas was the dominant group growing on Skeletonema costatum exudates during the exponential growth phase, but it was replaced by Roseobacter afterwards. On Micromonas pusilla exudates, Roseobacter was replaced by Bacteroidetes after the exponential growth phase. Our work shows that fluorescence excitation-emission matrices of CDOM can be a helpful tool for the identification of microbial sources of DOM in the marine environment, but further studies are necessary to explore the association of particular bacterial groups with specific fluorophores.     

Long term records of riverine dissolved organic matter

This presents the longest, consistent records of dissolved organic carbon in rivers ever published. This study presents long-term records of organic matter as indicated by water colour that were constructed for three catchments in Northern England for as far back as 1962. Observations show that there have been large increases in DOC concentrations over the period of study with in one case a doubling of the concentration over a period of 29 years. However, in one of the catchments no significant change was observed over a 31-year period. All catchments show common inter-annual control on carbon release in response to droughts, but no step increases in DOC concentrations were observed in response to such perturbations with pre-drought levels being restored within a period 3–4 years. Observed increasing trends do not correlate with changes in river discharge, pH, alkalinity or rainfall, but do coincide with increasing average summer temperatures in the region. The times series of DOC concentration over the period of the record appears stationary, but the distribution of daily values suggests a change in sources of colour over the increasing trend. The evidence supports a view that increases in carbon release are in equilibrium with temperature increases accentuated by land-use factors.     

Spatial variation in bacterial community and dissolved organic matter composition in groundwater near a eutrophic lake

Aquatic Ecology - The aim of this study was to reveal the variation in dissolved organic matter (DOM) components, bacterial community composition, and their co-relationships during groundwater...     

Simultaneous consumption and production of fluorescent dissolved organic matter by lake bacterioplankton

Recent evidence suggests a key role of bacterioplankton in shaping the composition of the dissolved organic matter (DOM) pool in aquatic systems, not only through consumption but also through production of specific compounds, but the latter process is still not well understood. We used a bioassay approach to assess the patterns in bacterial production and consumption of five fluorescent DOM pools in seven lakes and two streams in Southeastern Québec, Canada, and the links these patterns may have with key aspects of bacterial metabolism, DOM origin and nutrients availability. Total dissolved organic C declined by 3-15% during these incubations, whereas the specific DOM pools had very different dynamics: Two humic-like fractions accumulated in all incubations, with rates of production increasing as a function of bacterial growth efficiency, which itself increased with phosphorus concentrations. In contrast, two protein-like fractions and a third humic-like fraction either increased or declined over the course of the experiments. The net production or consumption of these pools appeared to be a function of the contribution of terrestrial C to bulk DOM (derived from δ(13) C of the DOM) and of total bacterial activity. Our results suggest that lake bacterioplankton play a dual role in DOM dynamics, as consumers and also producers, and that the interplay between DOM origin and nutrient availability appears to determine the net outcome of bacterial DOM processing, thus influencing the bulk DOM composition and its fate in these aquatic systems.     

Microbial transformation of labile dissolved organic matter into humic-like matter in seawater

Abstract Microbial transformation of labile, low molecular weight dissolved organic matter (DOM) into dissolved humic matter (DHM) was studied in seawater. Surface water samples were amended with [¹⁴C into ¹⁴CO₂, TO¹⁴C (total organic ¹⁴C), and PO¹⁴C (particulate organic ¹⁴C), was measured over time in confined samples. The humic and non-humic fractions of DO¹⁴C (dissolved organic ¹⁴C) were separated according to a common operational definition of DHM based on adsorption on XAD-8 macroporous resin. Both TO¹⁴C and non-humic DO¹⁴C decreased during the experiments. However, ¹⁴C-labelled DHM increased during the first week of the incubations, to a level where it comprised 15% of the TO¹⁴C remaining in the samples, or 3% of the initially added ¹⁴C. Towards the end of experiments (ca 70 days), the humic fraction of DO¹⁴C gradually approached the background level of poisoned control samples. Provided that the XAD-8 operational definition of DHM is accepted, this study indicates that humic matter may be formed in seawater within days from labile monomers such as glucose.     

Regulation of bacterial proteolytic activity at natural concentrations in dissolved organic matter in a maritime pond]

The regulation of the bacterial exoproteolytic activity, at natural substrate concentrations, was studied during the survey of an Atlantic coastal marine pond (France). The regulation of this activity occurs at two different levels: on the one hand, at the cellular level, the ectoenzyme synthesis is regulated by hydrolysis substrates, dissolved combined amino acids (DCAA), and end products, dissolved free amino acids (DFAA), in terms of the relative amounts available to the cell, and on the other hand, at the ecosystem level, i.e. the hydrolytic activity, by the total amounts of DCAA and DFAA in situ. The DFAA acts as an inhibitor in enzymatic synthesis; in contrast, dissolved proteins induce the enzymatic synthesis and the exoproteolytic activity. These results, obtained in natural concentration conditions, confirm the functioning in situ of the ectoenzymatic activity regulation model of Chróst, until now only validated in an enriched experimental medium.     

土壤溶解性有机质的特性与环境意义

土壤生态环境是一个复杂的多介质多界面体系,尽管关于土壤溶解性有机质 研究还不完善,但现有的研究表明,它是这一环境中最为活跃的化学组成之一。由于土壤溶解性有机质在C、N、P和S等营养元素的生物地球化学过程、成土过程、微生物的生长代谢过程、土壤有南分解和转化过程以及土壤污染物的迁移过程有着重要的作用,因此已成为土壤科学、生态科学和环境科学交叉领域的研究热点,本文从土壤溶解性有机质的提取方法、来源、组成、含量和影响因素、生物有效性及环境意义等方面的研究进展作了简要的论述,同时提出了未来的研究方向。