Enhancement of phenylpropanoid enzymes and lignin in Phalaenopsis orchid and their influence on plant acclimatisation at different levels of photosynthetic photon flux

Effects of three levels of photosynthetic photon flux (PPF: 60, 160 and 300 μmol m⁻²s⁻¹) were investigated in one-month-old Phalaenopsis plantlets acclimatised ex vitro. Optimal growth, chlorophyll and carotenoid concentations, and a high carotenoid:chlorophyll a ratio were obtained at 160 μmol m⁻²s⁻¹, while net CO₂ assimilation (A), stomatal conductance (g), transpiration rate (E) and leaf temperature peaked at 300 μmol m⁻²s⁻¹, indicating the ability of the plants to grow ex vitro. Adverse effects of the highest PPF were reflected in loss of chlorophyll, biomass, non-protein thiol and cysteine, but increased proline. After acclimatisation, glucose-6-phosphate dehydrogenase, shikimate dehydrogenase, phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol dehydrogenase (CAD) increased, as did lignin. Peroxidases (POD), which play an important role in lignin synthesis, were induced in acclimatised plants. Polyphenol oxidase (PPO) and β-glucosidase (β-GS) activities increased to a maximum in acclimatised plants at 300 μmol m⁻²s⁻¹. A positive correlation between PAL, CAD activity and lignin concentration was observed, especially at 160 and 300 μmol m⁻²s⁻¹. The study concludes that enhancement of lignin biosynthesis probably not only adds rigidity to plant cell walls but also induces defence against radiation stress. A PPF of 160 μmol m⁻²s⁻¹was suitable for acclimatisation when plants were transferred from in vitro conditions.     

Soil N and C trace gas fluxes and microbial soil N turnover in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary

During two intensive field campaigns in summer and autumn 2004 nitrogen (N₂O, NO/NO₂) and carbon (CO₂, CH₄) trace gas exchange between soil and the atmosphere was measured in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary. The climate can be described as continental temperate. Fluxes were measured with a fully automatic measuring system allowing for high temporal resolution. Mean N₂O emission rates were 1.5 μg N m⁻² h⁻¹ in summer and 3.4 μg N m⁻² h⁻¹ in autumn, respectively. Also mean NO emission rates were higher in autumn (8.4 μg N m⁻² h⁻¹) as compared to summer (6.0 μg N m⁻² h⁻¹). However, as NO₂ deposition rates continuously exceeded NO emission rates (−9.7 μg N m⁻² h⁻¹ in summer and −18.3 μg N m⁻² h⁻¹ in autumn), the forest soil always acted as a net NO _x sink. The mean value of CO₂ fluxes showed only little seasonal differences between summer (81.1 mg C m⁻² h⁻¹) and autumn (74.2 mg C m⁻² h⁻¹) measurements, likewise CH₄uptake (summer: −52.6 μg C m⁻² h⁻¹; autumn: −56.5 μg C m⁻² h⁻¹). In addition, the microbial soil processes net/gross N mineralization, net/gross nitrification and heterotrophic soil respiration as well as inorganic soil nitrogen concentrations and N₂O/CH₄ soil air concentrations in different soil depths were determined. The respiratory quotient (ΔCO_{2 resp} ΔO_{2 resp}⁻¹) for the uppermost mineral soil, which is needed for the calculation of gross nitrification via the Barometric Process Separation (BaPS) technique, was 0.8978 ± 0.008. The mean value of gross nitrification rates showed only little seasonal differences between summer (0.99 μg N kg⁻¹ SDW d⁻¹) and autumn measurements (0.89 μg N kg⁻¹ SDW d⁻¹). Gross rates of N mineralization were highest in the organic layer (20.1–137.9 μg N kg⁻¹ SDW d⁻¹) and significantly lower in the uppermost mineral layer (1.3–2.9 μg N kg⁻¹ SDW d⁻¹). Only for the organic layer seasonality in gross N mineralization rates could be demonstrated, with highest mean values in autumn, most likely caused by fresh litter decomposition. Gross mineralization rates of the organic layer were positively correlated with N₂O emissions and negatively correlated with CH₄ uptake, whereas soil CO₂ emissions were positively correlated with heterotrophic respiration in the uppermost mineral soil layer. The most important abiotic factor influencing C and N trace gas fluxes was soil moisture, while the influence of soil temperature on trace gas exchange rates was high only in autumn.     

Effects of sunlight on the production of dissolved organic and inorganic nutrients from resuspended sediments

A series of laboratory-based and field experiments was conducted to address the effects of sunlight-exposed resuspended sediments on dissolved nutrient fluxes in two different water bodies. In suspensions of tidal creek sediments in 0.2 μm-filtered creek water, measurable increases in dissolved nutrients occurred after only 2 h of exposure to simulated sunlight. During a 6-h irradiation, nutrient release rates for total dissolved nitrogen (TDN) and phosphate were 2.2 ± 0.5 (standard error; S.E.) μmol g^?1 h^?1 and 0.09 ± 0.005 μmol g^?1 h^?1 (S.E.), compared to no significant changes in dark controls. The majority of nitrogen was released as dissolved organic nitrogen (87% on average) with lesser amounts of ammonium (13%). Continental shelf sediments resuspended in unfiltered seawater also released phosphate and TDN when exposed to sunlight, suggesting that this process can occur in a variety of marine and estuarine environments. The source material for inorganic nutrients appears to be associated with sediments rather than dissolved organic matter, as no significant changes in nutrient concentrations occurred in experiments with 0.2 μm-filtered creek water or seawater alone. Results suggest that photoproduction of dissolved nutrients from resuspended sediments could be an episodically significant and previously unrecognized source of dissolved organic and inorganic nutrients to coastal ecosystems. This process may be especially important for continental margins where episodic resuspension events occur, as well as in regions experiencing high riverine sediment fluxes resulting from erosion associated with deforestation and desertification.     

Carbon Dioxide and Methane Fluxes From Tree Stems,Coarse Woody Debris,and Soils in an Upland Temperate Forest

Forest soils and canopies are major components of ecosystem CO₂ and CH₄ fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO₂ and CH₄ fluxes. We measured CO₂ and CH₄ fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO₂ sources (4.58 ± 2.46 µmol m^?2 s^?1, mean ± 1 SD) and net sinks of CH₄ (?2.17 ± 1.60 nmol m^?2 s^?1). Coarse woody debris was a CO₂ source (4.23 ± 3.42 µmol m^?2 s^?1) and net CH₄ sink, but with large uncertainty (?0.27 ± 1.04 nmol m^?2 s^?1) and with substantial differences depending on wood decay status. Stems were CO₂ sources (1.93 ± 1.63 µmol m^?2 s^?1), but also net CH₄ sources (up to 0.98 nmol m^?2 s^?1), with a mean of 0.11 ± 0.21 nmol m^?2 s^?1 and significant differences depending on tree species. Stems of N. sylvatica, F. grandifolia, and L. tulipifera consistently emitted CH₄, whereas stems of A. rubrum, B. lenta, and Q. spp. were intermittent sources. Coarse woody debris and stems accounted for 35% of total measured CO₂ fluxes, whereas CH₄ emissions from living stems offset net soil and CWD CH₄ uptake by 3.5%. Our results demonstrate the importance of CH₄ emissions from living stems in upland forests and the need to consider multiple forest components to understand and interpret ecosystem CO₂ and CH₄ dynamics.     

Nitrification and denitrification in a midwestern stream containing high nitrate: in situ assessment using tracers in dome-shaped incubation chambers

The extent to which in-stream processes alter or remove nutrient loads in agriculturally impacted streams is critically important to watershed function and the delivery of those loads to coastal waters. In this study, patch-scale rates of in-stream benthic processes were determined using large volume, open-bottom benthic incubation chambers in a nitrate-rich, first to third order stream draining an area dominated by tile-drained row-crop fields. The chambers were fitted with sampling/mixing ports, a volume compensation bladder, and porewater samplers. Incubations were conducted with added tracers (NaBr and either ¹⁵N[NO₃ ^?], ¹⁵N[NO₂ ^?], or ¹⁵N[NH₄ ⁺]) for 24–44 h intervals and reaction rates were determined from changes in concentrations and isotopic compositions of nitrate, nitrite, ammonium and nitrogen gas. Overall, nitrate loss rates (220–3,560 μmol N m^?2 h^?1) greatly exceeded corresponding denitrification rates (34–212 μmol N m^?2 h^?1) and both of these rates were correlated with nitrate concentrations (90–1,330 μM), which could be readily manipulated with addition experiments. Chamber estimates closely matched whole-stream rates of denitrification and nitrate loss using ¹⁵N. Chamber incubations with acetylene indicated that coupled nitrification/denitrification was not a major source of N₂ production at ambient nitrate concentrations (175 μM), but acetylene was not effective for assessing denitrification at higher nitrate concentrations (1,330 μM). Ammonium uptake rates greatly exceeded nitrification rates, which were relatively low even with added ammonium (3.5 μmol N m^?2 h^?1), though incubations with nitrite demonstrated that oxidation to nitrate exceeded reduction to nitrogen gas in the surface sediments by fivefold to tenfold. The chamber results confirmed earlier studies that denitrification was a substantial nitrate sink in this stream, but they also indicated that dissolved inorganic nitrogen (DIN) turnover rates greatly exceeded the rates of permanent nitrogen removal via denitrification.     

Biogeochemical processes at the sediment–water interface, Bombah Broadwater, Myall Lakes

Myall Lakes has experienced algal blooms in recent years which threaten water quality. Biomarkers, benthic fluxes measured with chambers, and pore water metabolites were used to identify the nature and reactivity of organic matter (OM) in the sediments of Bombah Broadwater (BB), and the processes controlling sediment-nutrient release into the overlying waters. The OM in the sediments was principally from algal sources although terrestrial OM was found near the Myall River. Terrestrial faecal matter was identified in muddy sediments and was probably sourced via runoff from farm lands. The reactive OM which released nutrients into the overlying waters was from diatoms, dinoflagellates and probably cyanobacteria. Microcystis filaments were observed in surface sediments. OM degradation rates varied between 5.3 and 47.1 mmol m^?2 day^?1 (64–565 mg m^?2 day^?1), were highest in the muddy sediments and sulphate reduction rates accounted for 20–40% of the OM degraded. Diatoms, being heavy sink rapidly, and are an important vector to transport catchment N and P to sites of denitrification and P-trapping in the sediments. Denitrification rates (mean ～4 mmol N m^?2 day^?1), up to 7 mmol N m^?2 day^?1 (105 mg N m^?2 day^?1) were measured, and denitrification efficiencies were highest (mean = 86 ± 4%) in the sandy sediments (～20% of the area of BB), but lower in the muddy sediments (mean = 63 ± 15%). These differences probably result from higher OM loads and anaerobic respiration in muddy sediments. Most DIP (>70%) from OM degradation was not released into overlying waters but remained trapped in surface sediments. Biophysical (advective) processes were responsible for the measured metabolite (O₂, CO₂, DSi, DIN and DIP) fluxes across the sediment–water interface.     

Net sediment N2 fluxes in a southern New England estuary: variations in space and time

Over the past three decades, Narragansett Bay has undergone various ecological changes, including significant decreases in water column chlorophyll a concentrations, benthic oxygen uptake, and benthic nutrient regeneration rates. To add to this portrait of change, we measured the net flux of N₂ across the sediment–water interface over an annual cycle using the N₂/Ar technique at seven sites in the bay for comparison with measurements made decades ago. Net denitrification rates ranged from about 10–90 μmol N₂–N m^?2 h^?1 over the year. Denitrification rates were not significantly different among sites and had no clear correlation with temperature. Net nitrogen fixation (?5 to ?650 μmol N₂–N m^?2 h^?1) was measured at three sites and only observed in summer (June–August). Neither denitrification nor nitrogen fixation exhibited a consistent relationship with sediment oxygen demand or with fluxes of nitrite, nitrate, ammonium, total dissolved inorganic nitrogen, or dissolved inorganic phosphate across all stations. In contrast to the mid-bay historical site where denitrification rates have declined, denitrification rates in the Providence River Estuary have not changed significantly over the past 30 years.     

Nitrogen removal in coastal sediments of the German Wadden Sea

Although sediments of the German Wadden Sea are suspected to eliminate a considerable share of nitrate delivered to the SE North Sea, their denitrification rates have not been systematically assessed. We determined N₂ production rates over seasonal cycles (February 2009–April 2010) at two locations with two sediments types each, the first site (Meldorf Bight) receiving nitrate during all seasons from the Elbe river plume, and a second site on the island of Sylt, where nitrate is depleted during summer months. In sediments from the Sylt site, N₂ production ranged from 15 to 32 μmol N₂ m^?2 h^?1 in the fine sand station and from 7 to 13 μmol N₂ m^?2 h^?1 in the coarse sand station; N₂ production was not detected when nitrate was depleted in May and July of 2009. N₂ production in the Meldorf Bight sediments were consistently detected at higher rates (58–130 μmol N₂ m^?2 h^?1 in the very fine sand station and between 14 and 30 μmol N₂ m^?2 h^?1 in the medium sand station). Analysis of ancillary parameters suggests that major factors controlling N₂ production in coastal sediments of the German Wadden Sea are the nitrate concentrations in the overlying water, the ambient temperature, and the organic matter content of the sediment. Extrapolating our spot measurements to the zone of nitrate availability and sediment types, we estimate an annual nitrogen removal rate around 16 kt N year^?1 for the entire northern sector of the German Wadden Sea area. This corresponds to 14% of the annual Elbe river nitrogen load.     

Seasonal variability of methane in the rivers and lagoons of Ivory Coast (West Africa)

We report a data-set of dissolved methane (CH₄) in three rivers (Comoé, Bia and Tanoé) and five lagoons (Grand-Lahou, Ebrié, Potou, Aby and Tendo) of Ivory Coast (West Africa), during the four main climatic seasons (high dry season, high rainy season, low dry season and low rainy season). The surface waters of the three rivers were over-saturated in CH₄ with respect to atmospheric equilibrium (2221–38719%), and the seasonal variability of CH₄ seemed to be largely controlled by dilution during the flooding period. The strong correlation of CH₄ concentrations with the partial pressure of CO₂ (pCO₂) and dissolved silicate (DSi) confirm the dominance of a continental sources (from soils) for both CO₂ and CH₄ in these rivers. Diffusive air–water CH₄ fluxes ranged between 25 and 1187 μmol m^?2 day^?1, and annual integrated values were 288 ± 107, 155 ± 38, and 241 ± 91 μmol m^?2 day^?1 in the Comoé, Bia and Tanoé rivers, respectively. In the five lagoons, surface waters were also over-saturated in CH₄ (ranging from 1496 to 51843%). Diffusive air–water CH₄ fluxes ranged between 20 and 2403 μmol m^?2 day^?1, and annual integrated values were 78 ± 34, 338 ± 217, 227 ± 79, 330 ± 153 and 326 ± 181 μmol m^?2 day^?1 in the Grand-Lahou, Ebrié, Potou, Aby and Tendo lagoons, respectively. The largest CH₄ over-saturations were observed in the Tendo and Aby lagoons that are permanently stratified systems (unlike the other three lagoons), leading to anoxic bottom waters favorable for a large CH₄ production. In addition, these two stratified lagoons showed low pCO₂ values due to high primary production, which suggests an efficient transfer of organic matter across the pycnocline. As a result, the stratified Tendo and Aby lagoons were respectively, a low source of CO₂ to the atmosphere and a sink of atmospheric CO₂ while the other three well-mixed lagoons were strong sources of CO₂ to the atmosphere but less over-saturated in CH₄.     

Analysis of the <Emphasis Type="Italic">xynB5</Emphasis> gene encoding a multifunctional GH3-BglX β-glucosidase-β-xylosidase-α-arabinosidase member in <Emphasis Type="Italic">Caulobacter crescentus</Emphasis>

The Caulobacter crescentus (NA1000) xynB5 gene (CCNA_03149) encodes a predicted β-glucosidase-β-xylosidase enzyme that was amplified by polymerase chain reaction; the product was cloned into the blunt ends of the pJet1.2 plasmid. Analysis of the protein sequence indicated the presence of conserved glycosyl hydrolase 3 (GH3), β-glucosidase-related glycosidase (BglX) and fibronectin type III-like domains. After verifying its identity by DNA sequencing, the xynB5 gene was linked to an amino-terminal His-tag using the pTrcHisA vector. A recombinant protein (95 kDa) was successfully overexpressed from the xynB5 gene in E. coli Top 10 and purified using pre-packed nickel-Sepharose columns. The purified protein (BglX-V-Ara) demonstrated multifunctional activities in the presence of different substrates for β-glucosidase (pNPG: p-nitrophenyl-β-D-glucoside) β-xylosidase (pNPX: p-nitrophenyl-β-D-xyloside) and α-arabinosidase (pNPA: p-nitrophenyl-α-L-arabinosidase). BglX-V-Ara presented an optimal pH of 6 for all substrates and optimal temperature of 50 °C for β-glucosidase and α-l-arabinosidase and 60 °C for β-xylosidase. BglX-V-Ara predominantly presented β-glucosidase activity, with the highest affinity for its substrate and catalytic efficiency (K_m 0.24 ± 0.0005 mM, V_max 0.041 ± 0.002 µmol min^?1 mg^?1 and K_cat/K_m 0.27 mM^?1 s^?1), followed by β-xylosidase (K_m 0.64 ± 0.032 mM, V_max 0.055 ± 0.002 µmol min^?1 mg^?1 and K_cat/K_m 0.14 mM^?1s^?1) and finally α-l-arabinosidase (K_m 1.45 ± 0.05 mM, V_max 0.091 ± 0.0004 µmol min^?1 mg^?1 and K_cat/K_m 0.1 mM^?1 s^?1). To date, this is the first report to demonstrate the characterization of a GH3-BglX family member in C. crescentus that may have applications in biotechnological processes (i.e., the simultaneous saccharification process) because the multifunctional enzyme could play an important role in bacterial hemicellulose degradation.     

Feeding and digestive responses to fatty acid intake in two South American passerines with different food habits

Specific fatty acids (FA) such as unsaturated (UFA) and saturated (SFA) fatty acids contained in foods are key factors in the nutritional ecology of birds. By means of a field and experimental approach, we evaluated the effect of diet on the activity of three esterases involved in FA hydrolysis; carboxylesterase (CE: 4-NPA-CE and a-NA-CE) and butyrylcholinesterase, in two South American passerines: the omnivorous rufous-collared sparrow (Zonotrichia capensis) and the granivorous common diuca-finch (Diuca diuca). The activity of the three esterases was measured in the intestines of freshly caught individuals over two distinct seasons and also after a chronic intake of a UFA-rich or SFA-rich diet in the laboratory. In turn, we assessed the feeding responses of the birds choosing amongst diets contrasting in the kind of specific FA (UFA- vs. SFA-treated diets). During summer, field CE activities (4-NPA-CE and a-NA-CE) in the small intestine were higher in the rufous-collared sparrow (25.3 ± 3.3 and 81.4 ± 10.8 µmol min^?1 g tissue^?1, respectively) than in the common diuca-finch (10.0 ± 3.0 and 33.9 ± 13.1 µmol min^?1 g tissue^?1, respectively). Two hour feeding trial test indicated that both species exhibited a clear preference for UFA-treated diets. On average, the rufous-collared sparrow consumed 0.46 g 2 h^?1 of UFA-rich diets and 0.12 g 2 h^?1 of SFA-rich diets. In turn, the consumption pattern of the common diuca-finch averaged 0.73 and 0.16 g 2 h^?1 for UFA-rich and SFA-rich diets, respectively. After a month of dietary acclimation to UFA-rich and SFA-rich diets, both species maintained body mass irrespective of the dietary regime. Additionally, the intestinal 4-NPA-CE activity exhibited by birds fed on a UFA-rich or SFA-rich diet was higher in the rufous-collared sparrow (39.0 ± 5.3 and 44.2 ± 7.3 µmol min^?1 g tissue^?1, respectively) than in the common diuca-finch (13.3 ± 1.9 and 11.2 ± 1.4 µmol min^?1 g tissue^?1, respectively). Finally, the intestinal a-NA-CE activity exhibited by the rufous-collared sparrow was about two times higher when consuming an UFA-rich diet. Our results suggest that the rufus-collared sparrow exhibits a greater capacity for intestinal FA hydrolysis, which would allow it to better deal with fats from different sources.     

PAR modulation of the UV-dependent levels of flavonoid metabolites in Arabidopsis thaliana (L.) Heynh. leaf rosettes: cumulative effects after a whole vegetative growth period

Long-term effects of ultraviolet (UV) radiation on flavonoid biosynthesis were investigated in Arabidopsis thaliana using the sun simulators of the Helmholtz Zentrum München. The plants, which are widely used as a model system, were grown (1) at high photosynthetically active radiation (PAR; 1,310 µmol m^?2?s^?1) and high biologically effective UV irradiation (UV-B_BE 180 mW m^?2) during a whole vegetative growth period. Under this irradiation regime, the levels of quercetin products were distinctively elevated with increasing UV-B irradiance. (2) Cultivation at high PAR (1,270 µmol m^?2?s^?1) and low UV-B (UV-B_BE 25 mW m^?2) resulted in somewhat lower levels of quercetin products compared to the high-UV-B_BE conditions, and only a slight increase with increasing UV-B irradiance was observed. On the other hand, when the plants were grown (3) at low PAR (540 µmol m^?2?s^?1) and high UV-B (UV-B_BE 180 mW m^?2), the accumulation of quercetin products strongly increased from very low levels with increasing amounts of UV-B but the accumulation of kaempferol derivatives and sinapoyl glucose was less pronounced. We conclude (4) that the accumulation of quercetin products triggered by PAR leads to a basic UV protection that is further increased by UV-B radiation. Based on our data, (5) a combined effect of PAR and different spectral sections of UV radiation is satisfactorily described by a biological weighting function, which again emphasizes the additional role of UV-A (315–400 nm) in UV action on A. thaliana.     

Ecosystem respiration derived from 222Rn measurements on Rishiri Island, Japan

We evaluated the nighttime CO₂ flux (ecosystem respiration) on Rishiri Island, located at the northern tip of Hokkaido, Japan, from 2009 to 2011, by using the relationship between atmospheric ²²²Rn and CO₂ concentrations. The annual mean CO₂ flux was 1.8 μmol m^?2 s^?1, with a maximum monthly mean in July (4.6 ± 2.6 μmol m^?2 s^?1) and a broad minimum from December to March (0.33 ± 0.29 μmol m^?2 s^?1). The annual mean was comparable to fluxes at the JapanFlux sites in northern Japan. During the season of snow cover (mid-December to early April), the CO₂ flux was low (0.45 ± 0.43 μmol m^?2 s^?1). Total annual respiration was estimated at 679 ± 174 g cm^?2, about 8 % of which occurred during the season of snow cover.     

Spatial and temporal dynamics of diffusive methane emissions in the Okavango Delta,northern Botswana,Africa

Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH₄) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH₄ in the world contributing between 100 and 231 Tg year^?1 to the total budget of 503–610 Tg year^?1, approximately 60 % of which is emitted from tropical wetlands. We conducted diffusive CH₄ emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH₄ emission rates varied between 0.24 and 293 mg CH₄ m^?2 h^?1, with a mean (±SE) emission of 23.2 ± 2.2 mg CH₄ m^?2 h^?1 or 558 ± 53 mg CH₄ m^?2 day^?1. These emission rates lie within the range reported for other tropical wetlands. The emission rates were significantly higher (P < 0.007) in permanent than in seasonal swamps. River channels exhibited the highest average fluxes at 31.3 ± 5.4 mg CH₄ m^?2 h^?1 than in floodplains (20.4 ± 2.5 mg CH₄ m^?2 h^?1) and lagoons (16.9 ± 2.6 mg CH₄ m^?2 h^?1). Diffusive CH₄ emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH₄ m^?2 h^?1) and lowest (0.2–3.0 mg m^?2 h^?1) during the warmer-rainy and cooler winter seasons, respectively. Surface water temperatures between December 2010 and January 2012 varied from 15.3 °C in winter to 33 °C in summer. Assuming mean inundation of 9,000 km², the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH₄ emission from global tropical wetlands.     

Effects of floating vegetation on denitrification,nitrogen retention,and greenhouse gas production in wetland microcosms

Wetlands are biogeochemical hotspots that have been identified as important sites for both nitrogen (N) removal from surface waters and greenhouse gas (GHG) production. Floating vegetation (FV) commonly occurs in natural and constructed wetlands, but the effects of such vegetation on denitrification, N retention, and GHG production are unknown. To address this knowledge gap, we used microcosm experiments to examine how FV affects N and GHG dynamics. Denitrification and N retention rates were significantly higher in microcosms with FV (302 μmol N m^?2 h^?1 and 203 μmol N m^?2 h^?1, respectively) than in those without (63 μmol N m^?2 h^?1 and 170 μmol N m^?2 h^?1, respectively). GHG production rates were not significantly different between the two treatments. Denitrification rates were likely elevated due to decreased dissolved oxygen (DO) in microcosms with FV. The balance of photosynthesis and respiration was more important in affecting DO concentrations than decreased surface gas exchange. The denitrification fraction (N₂-N production: N retention) was higher in microcosms with FV (100 %) than those without (33 %) under increased (tripled) N loading. A 5 °C temperature increase resulted in significantly lower denitrification rates in the absence of FV and significantly lowered N₂O production with FV, but did not significantly change CH₄ production or N retention in either treatment. These results suggest that intentional introduction of FV in constructed wetlands could enhance N removal while leaving GHG production unchanged, an insight that should be further tested via in situ experiments.     

Tobermolite effects on methane removal activity and microbial community of a lab-scale soil biocover

Three identical lab-scale biocovers were packed with an engineered soil (BC 1), tobermolite only (BC 2), and a mixture of the soil and tobermolite (BC 3), and were operated at an inlet load of 338–400 g-CH₄ m^?2 d^?1 and a space velocity of 0.12 h^?1. The methane removal capacity was 293 ± 47 g-CH₄ m^?2 d^?1 in steady state in the BC 3, which was significantly higher than those in the BC 1 and BC 2 (106 ± 24 and 114 ± 48 g-CH₄ m^?2 d^?1, respectively). Quantitative PCR indicated that bacterial and methanotrophic densities (6.62–6.78 × 10⁷ 16S rDNA gene copy number g-dry sample^?1 and 1.37–2.23 × 10⁷ pmoA gene copy number g-dry sample^?1 in the BC 1 and BC 3, respectively) were significantly higher than those in the BC 2. Ribosomal tag pyrosequencing showed that methanotrophs comprised approximately 60 % of the bacterial community in the BC 2 and BC 3, while they only comprised 43 % in the BC 1. The engineered soil favored the growth of total bacteria including methanotrophs, while the presence of tobermolite enhanced the relative abundance of methanotrophs, resulting in an improved habitat for methanotrophs as well as greater methane mitigation performance in the mixture. Moreover, a batch experiment indicated that the soil and tobermolite mixture could display a stable methane oxidation level over wide temperature (20–40 °C, at least 38 μmol g-dry sample^?1 h^?1) and pH (5–8, at least 61 μmol g-dry sample^?1 h^?1) ranges. In conclusion, the soil and tobermolite mixture is promising for methane mitigation.     

Adaptations of tropical marine microphytobenthic assemblages along a gradient of light and nutrient availability in Suva Lagoon,Fiji

How are microphytobenthic biofilms adapted to the high incident irradiances and temperatures, low inorganic nutrient concentrations and high desiccation stresses on intertidal flats present in tropical environments? This study investigated biofilms subject to different environmental conditions in a range of tropical sites in Suva lagoon, Fiji. PAM fluorescence was used to measure photophysiological responses to the light climate. Biofilm colloidal carbohydrate, extracellular polymeric substances (EPS) and low molecular weight (MW) carbohydrate concentrations and diel carbohydrate production patterns were measured. Average biomass (Chl a) ranged from 15 to 36?mg?m^?2, and was highest in seagrass bed sediments, but biomass was not correlated with water column or sediment porewater nutrient concentrations. Biofilm photophysiology differed significantly along a combined gradient of light and nutrient availability, with F _v/F _m, relative ETR_max and E _k of biofilms highest in mangrove and intertidal main island sites and lowest in subtidal coral reef flats. Subtidal biofilms showed photoinhibition at irradiances > 1000?µmol?m^?2. Significant correlations between Chl a and colloidal carbohydrate concentrations were present (except on intertidal sandflats), and tropical biofilms had higher ratios of colloidal carbohydrate and EPS to Chl a than temperate estuarine biofilms, probably due to a combination of high irradiance and low nutrient availability leading to the production of excess photoassimilates. The percentage of EPS present in the colloidal fraction was highest in coral sand biofilms (42%), which had the lowest nutrient concentrations, compared with other sites (25–32%). Intertidal biofilms predominantly consisted of large motile taxa and showed strong rhythms of vertical migration. During tidal emersion, high sediment temperatures (41?°C), irradiance (>2300?µmol?m^?2?s^?1) and salinity (49‰) stimulated downward migration. In silty sediments, migration resulted in a reduction in photosynthetic activity during the midday period but, in sands with high light penetration (to a depth of > 1700?µm), high production rates of EPS (18.2?µg carbo. µg Chl a^?1 h^?1) and low MW carbohydrate exudates (40.2?µg carbo. µg Chl a^?1 h^?1) occurred. Vertical migration, high E _k and high rates of photoassimilate dumping are all adaptations to living in the tropical intertidal zone. Seagrass and reef flat biofilms consisted of a diverse non-migratory flora of motile and non-motile taxa that were not subject to such extreme temperature and irradiance conditions. Low values of photosynthetic parameters and high colloidal and EPS content indicated that these biofilms were nutrient-limited.     

Influence of hydrological connectivity of riverine wetlands on nitrogen removal via denitrification

Wetland ecosystems in agricultural areas often become progressively more isolated from main water bodies. Stagnation favors the accumulation of organic matter as the supply of electron acceptors with water renewal is limited. In this context it is expected that nitrogen recycling prevails over nitrogen dissipation. To test this hypothesis, denitrification rates, fluxes of dissolved oxygen (SOD), inorganic carbon (DIC) and nitrogen and sediment features were measured in winter and summer 2007 on 22 shallow riverine wetlands in the Po River Plain (Northern Italy). Fluxes were determined from incubations of intact cores by measurement of concentration changes or isotope pairing in the case of denitrification. Sampled sites were eutrophic to hypertrophic; 10 were connected and 12 were isolated from the adjacent rivers, resulting in large differences in nitrate concentrations in the water column (from <5 to 1,133 μM). Benthic metabolism and denitrification rates were investigated by two overarching factors: season and hydrological connectivity. SOD and DIC fluxes resulted in respiratory quotients greater than one at most sampling sites. Sediment respiration was coupled to both ammonium efflux, which increased from winter to summer, and nitrate consumption, with higher rates in river-connected wetlands. Denitrification rates measured in river-connected wetlands (35–1,888 μmol N m^?2 h^?1) were up to two orders of magnitude higher than rates measured in isolated wetlands (2–231 μmol N m^?2 h^?1), suggesting a strong regulation of the process by nitrate availability. These rates were also significantly higher in summer (9–1,888 μmol N m^?2 h^?1) than in winter (2–365 μmol N m^?2 h^?1). Denitrification supported by water column nitrate (D_W) accounted for 60–100% of total denitrification (Dtot); denitrification coupled to nitrification (D_N) was probably controlled by limited oxygen availability within sediments. Denitrification efficiency, calculated as the ratio between N removal via denitrification and N regeneration, and the relative role of denitrification for organic matter oxidation, were high in connected wetlands but not in isolated sites. This study confirms the importance of restoring hydraulic connectivity of riverine wetlands for the maintenance of important biogeochemical functions such as nitrogen removal via denitrification.     

Fed-Batch Cultivation of Arthrospira platensis Using Carbon Dioxide from Alcoholic Fermentation and Urea as Carbon and Nitrogen Sources

To reduce CO₂ emissions from alcoholic fermentation, Arthrospira platensis was cultivated in tubular photobioreactor using either urea or nitrate as nitrogen sources at different light intensities (60 μmol m^?2 s^?1?≤?I?≤?240 μmol m^?2 s^?1). The type of carbon source (pure CO₂ or CO₂ from fermentation) did not show any appreciable influence on the main cultivation parameters, whereas substitution of nitrate for urea increased the nitrogen-to-cell conversion factor (Y _X/N ), and the maximum cell concentration (X _m ) and productivity (P _X ) increased with I. As a result, the best performance using gaseous emissions from alcoholic fermentation (X _m ?=?2,960?±?35 g m^?3, P _X ?=?425?±?5.9 g m^?3 day^?1 and Y _X/N ?=?15?±?0.2 g g^?1) was obtained at I?=?120 μmol m^?2 s^?1 using urea as nitrogen source. The results obtained in this work demonstrate that the combined use of effluents rich in urea and carbon dioxide could be exploited in large-scale cyanobacteria cultivations to reduce not only the production costs of these photosynthetic microorganisms but also the environmental impact associated to the release of greenhouse emissions.     

Biogeochemical regime shifts in coastal landscapes: the contrasting effects of saltwater incursion and agricultural pollution on greenhouse gas emissions from a freshwater wetland

Many coastal plain wetlands receive nutrient pollution from agricultural fields and are particularly vulnerable to saltwater incursion. Although wetlands are a major source of the greenhouse gases methane (CH₄) and nitrous oxide (N₂O), the consequences of salinization for greenhouse gas emissions from wetlands with high agricultural pollution loads is rarely considered. Here, we asked how saltwater exposure alters greenhouse gas emissions from a restored freshwater wetland that receives nutrient loading from upstream farms. During March to November 2012, we measured greenhouse gases along a ~2 km inundated portion of the wetland. Sampling locations spanned a wide chemical gradient from sites receiving seasonal fertilizer nitrogen and sulfate (SO₄ ^2?) loads to sites receiving seasonal increases in marine salts. Concentrations and fluxes of CH₄ were low (<100 µg L^?1 and <10 mg m^?2 h^?1) for all sites and sampling dates when SO₄ ^2? was high (>10 mg L^?1), regardless of whether the SO₄ ^2? source was agriculture or saltwater. Elevated CH₄ (as high as 1,500 µg L^?1 and 45 mg m^?2 h^?1) was only observed on dates when air temperatures were >27 °C and SO₄ ^2? was <10 mg L^?1. Despite elevated ammonium (NH₄ ⁺) for saltwater exposed sites, concentrations of N₂O remained low (<5 µg L^?1 and <10 µg m^?2 h^?1), except when fertilizer derived nitrate (NO₃ ^?) concentrations were high and N₂O increased as high as 156 µg L^?1. Our results suggest that although both saltwater and agriculture derived SO₄ ^2? may suppress CH₄, increases in N₂O associated with fertilizer derived NO₃ ^? may offset that reduction in wetlands exposed to both agricultural runoff and saltwater incursion.