The dissolved organic nutrient conditions and bacterial process rates at two tropical coastal sites in Peninsular Malaysia (Port Klang and Port Dickson) were initially studied in 2004–2005 period and ...later revisited in 2010–2011. We observed that dissolved organic nitrogen (DON) increased about two- and ten-fold at Port Klang and Port Dickson, respectively and resulted in a significant change in DOC:DON ratio (t ≥ 2.077, p < 0.05). Among the bacterial processes measured, bacterial respiration (BR) was lower in the 2010–2011 period at both stations (t ≥ 3.390, p < 0.01). BR also correlated to the DOC:DON ratio (R2 ≥ 0.259, p < 0.01). The increase in substrate quality enabled the bacteria to respire less in the dissolved organic matter degradation. As a result, the average bacterial growth efficiency increased slightly in the 2010–2011 period.
•Long-term comparison showed an increase in dissolved organic nitrogen (DON).•Increase in DON reduced the DOC:DON ratio and increased substrate quality.•Bacterial respiration decreased with the increase in substrate quality.
Freshwater emits substantial volumes of CO 2 to the atmosphere. This has largely gone unnoticed in global carbon budgets. My aim was to quantify the CO 2 emanating from freshwater from 66° N to 47° S ...latitudes via in situ bacterial respiration (BR). I determined BR ( n = 326) as a function of water temperature. Freshwater is emitting CO 2 at a rate of 58.5 Pg C y −1 (six times that of fossil fuel burning). Most is emitted from the Northern Hemisphere. This is because the high northern summer temperatures coincide with most of the world’s freshwater. Diffuse DOC sources, for example dust, may be driving high freshwater BR. However, many sources remain elusive and not individually quantified in the literature. We must include freshwater CO 2 emissions in climate models. Identifying, quantifying and managing freshwater’s diffuse sources of Dissolved Organic Carbon (DOC) will hopefully provide us with another opportunity to change our current climate trajectory.
The Earth's subsurface represents a complex electrochemical environment that contains many electro-active chemical compounds that are relevant for a wide array of biologically driven ecosystem ...processes. Concentrations of many of these electro-active compounds within Earth's subsurface environments fluctuate during the day and over seasons. This has been observed for surface waters, sediments and continental soils. This variability can affect particularly small, relatively immobile organisms living in these environments. While various drivers have been identified, a comprehensive understanding of the causes and consequences of spatio-temporal variability in subsurface electrochemistry is still lacking. Here we propose that variations in atmospheric electricity (AE) can influence the electrochemical environments of soils, water bodies and their sediments, with implications that are likely relevant for a wide range of organisms and ecosystem processes. We tested this hypothesis in field and laboratory case studies. Based on measurements of subsurface redox conditions in soils and sediment, we found evidence for both local and global variation in AE with corresponding patterns in subsurface redox conditions. In the laboratory, bacterial respiratory responses, electron transport activity and H
S production were observed to be causally linked to changes in atmospheric cation concentrations. We argue that such patterns are part of an overlooked phenomenon. This recognition widens our conceptual understanding of chemical and biological processes in the Earth's subsurface and their interactions with the atmosphere and the physical environment.
Climate change affects glaciers all over the world causing glacial recession with the formation of new lakes. Glaciers of Mount Tronador (41° S, Patagonia, Argentina) underwent an increase of more ...than 200 m in the equilibrium‐line altitude (ELA), from 1994 to 2016. The proglacial Lake Ventisquero Negro showed a continuous increase in lake surface area since 2009, when a glacial outburst flood (GLOF) occurred. The Ventisquero Negro glacier is a debris‐covered glacier located below the timberline; thus, the lake receives meltwater from both clean and debris‐rich ice.
This study analyses the proglacial lake after the GLOF event, particularly the nutrient content, dissolved organic matter and bacterial respiration. Our main hypothesis was that the melting of debris‐rich and clean ice would differentially affect nutrient inputs and bacterial respiration in the early ontogeny of the lake.
Sampling was conducted in austral spring–summer seasons (2012 to 2016) following the GLOF event. We carried out bacterial respiration experiments with lake water and two treatments enriched with clean or debris‐rich ice from the glacier. Additionally, we carried out an another enrichment experiment with phosphate‐P and glucose‐C alone or in combination.
The lake exhibited high turbidity levels due to a high concentration of suspended solids. Vertical light profiles showed that almost the entire water column was aphotic. Phosphorus (P) concentration was high and was positively related to total suspended solids. Accordingly, P concentration was higher in debris‐rich than in clean ice. However, the dissolved organic carbon concentrations in the lake were found to remain relatively constant through time (less than 50 μmol/L).
Analysing fluorescent excitation–emission matrices, we determined that the dissolved organic matter is very simple with only two peaks, one corresponding to protein‐like compounds (C1) and the other to humic‐like compounds (C2), coming from clean ice and debris‐rich ice, respectively. C1 was present in all samples, while C2 was comparatively more important during summer, coinciding with higher temperatures and melting.
This study supports the hypothesis that melting of clean and debris‐rich ice would affect DOM and P input at early stages of a proglacial lake formed by the recession of a debris‐covered glacier. Bacterial respiration was observed to be positively affected by debris‐rich ice melting and to be P limited. Thus, P is a major controlling factor for carbon dynamics in a newly formed proglacial lake.
Our view of the effects of temperature on bacterial carbon fluxes in the ocean has been confounded by the interplay of resource availability. Using extensive compilation of cell-specific bacterial ...respiration (BRi) and production (BPi), we show that both physiological rates respond to changing temperature in a similar manner and follow the predictions of the metabolic theory of ecology. Their apparently different temperature dependence under warm, oligotrophic conditions is due to strong resource limitation of BPi but not of BRi. Thus, and despite previous preconception, bacterial growth efficiency (BGE = BPi/BPi + BRi) is not directly regulated by temperature, but by the availability of substrates for growth. We develop simple equations that can be used for the estimation of bacterial community metabolism from temperature, chlorophyll concentration, and bacterial abundance. Since bacteria are the greatest living planktonic biomass, our results challenge current understanding of how warming and shifts in ecosystem trophic state will modify oceanic carbon cycle feedbacks to climate change.
Dissolved organic matter (DOM) input is a key factor for freshwater ecology, since it regulates many aspects of aquatic ecosystem metabolism. Aquatic and terrestrial animals that inhabit or frequent ...aquatic environments also influence the DOM inputs via their faeces, supplying nutrients such as carbon (C), nitrogen (N), and phosphorus (P). Here, we analyse the response of a bacterial community in the newly formed proglacial Lake Ventisquero Negro (Mount Tronador) to the addition of dissolved nutrients from faeces leachate of the native goose (
Chloephaga poliocephala
Sclater, 1857; locally called “cauquén”) and the European hare (
Lepus europaeus
Pallas, 1778). A laboratory incubation experiment was carried out with unenriched lake water and lake water enriched with leachate from hare or goose faeces. The results showed that faeces and leachates of geese were richer in nutrients than those of hares. Spectrofluorometric analysis of the DOM also showed differences between the two sources. Nutrient enrichment positively affected bacterial respiration and short-term carbon consumption. Thus, the faeces of these two animals may play an important ecological role by supplying allochthonous DOM and nutrients to this new ecosystem.
Plankton community respiration (R) is a major component of the carbon flux in aquatic ecosystems. However, current methods to measure actual respiration from oxygen consumption at relevant spatial ...scales are not sensitive enough in oligotrophic environments where respiration rates are very low. To overcome this drawback, more sensitive indirect enzymatic approaches are commonly used as R proxies. The in vivo electron transport system (ETSvivo) assay, which measures the reduction of (2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl tetrazolium chloride salt, INT) to INT-formazan in the presence of natural substrate levels, was recently proposed as an indirect reliable estimation of R for natural plankton communities. However, under in vivo conditions, formazan salts could be toxic to the cells. Here, we test the toxicity of 0.2 mM of final INT concentration, widely used for ETSvivo assays, on natural bacterial assemblages collected in coastal and oceanic waters off Gran Canaria (Canary Islands, subtropical North Atlantic), in eight independent experiments. After 0.5 h of incubation, a significant but variable decline in cell viability (14–49%) was observed in all samples inoculated with INT. Moreover, INT also inhibited leucine uptake in less than 90 min of incubation. In the light of these results, we argue that enzymatic respiratory rates obtained with the ETSvivo method need to be interpreted with caution to derive R in oceanic regions where bacteria largely contribute to community respiration. Moreover, the variable toxicity on bacterial assemblages observed in our experiments questions the use of a single R/ETSvivo relationship as a universal proxy for regional studies.
In the Northern Patagonian Andes, the austral beech Nothofagus pumilio dominates the upper limit of the temperate forest and is an important source of allochthonous dissolved organic matter (DOM) in ...mountain lakes. In addition, shallow lakes in these mountains develop benthic algal assemblages (Spirogyra and Mougeotia) that provide autochthonous DOM. We assessed the effect of differences in the nutritional quality of these DOM inputs on bacterial metabolism in a mountain lake located in Northern Patagonia (Argentina). We analyzed DOM lability and changes in bacterial assemblages experimentally by enriching treatments with either algal exudates (+EXU) or senescent N. pumilio leaf leachates (+LEA) together with a control without enrichment (−ENR). We determined nutrient concentrations and DOM optical properties with spectrofluorometric excitation-emission matrix analysis. We also assessed bacterial assemblage composition by next-generation sequencing the 16S rRNA gene. DOM optical properties and phosphorus (P) content differed among treatments. The +LEA treatment had a lower C∶P ratio (more P content) than the +EXU treatment. In addition, DOM optical characterization revealed that 1 protein-like compound (tryptophan) was present in the +LEA treatment, but a different protein-like compound (tyrosine) was present in the +EXU treatment. The +LEA treatment had higher bacterial respiration rates than the control, particularly during the first 2 d of incubation. These higher respiration rates were probably a result of the lower C∶P ratio and the difference in fluorescence compounds. However, the bacterial assemblage composition did not change in the different treatments. Our study suggests that high relative P content from allochthonous DOM increases bacterial C-consumption and highlights the importance of C∶nutrient ratios in DOM for C-cycling in aquatic ecosystems.
The Na
+
-translocating NADH:quinone oxidoreductase (Na
+
-NQR) is a unique Na
+
pumping respiratory complex found only in prokaryotes, that plays a key role in the metabolism of marine and ...pathogenic bacteria, including
Vibrio cholerae
and other human pathogens. Na
+
-NQR is the main entrance for reducing equivalents into the respiratory chain of these bacteria, catalyzing the oxidation of NADH and the reduction of quinone, the free energy of this redox reaction drives the selective translocation of Na
+
across the cell membrane, which energizes key cellular processes. In this review we summarize the unique properties of Na
+
-NQR in terms of its redox cofactor composition, electron transfer reactions and a possible mechanism of coupling and pumping.
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