共查询到20条相似文献,搜索用时 15 毫秒
1.
To identify the controls on dissolved organic carbon (DOC) production, we incubated soils from 18 sites, a mixture of 52 forest
floor and peats and 41 upper mineral soil samples, at three temperatures (3, 10, and 22°C) for over a year and measured DOC
concentration in the leachate and carbon dioxide (CO2) production from the samples. Concentrations of DOC in the leachate were in the range encountered in field soils (<2 to >50 mg l−1). There was a decline in DOC production during the incubation, with initial rates averaging 0.03–0.06 mg DOC g−1 soil C day−1, falling to averages of 0.01 mg g−1 soil C day−1; the rate of decline was not strongly related to temperature. Cumulative DOC production rates over the 395 days ranged from
less than 0.01 to 0.12 mg g−1 soil C day−1 (0.5–47.6 mg g−1 soil C), with an average of 0.021 mg g−1 soil C day−1 (8.2 mg g−1 soil C). DOC production rate was weakly related to temperature, equivalent to Q10 values of 0.9 to 1.2 for mineral samples and 1.2 to 1.9 for organic samples. Rates of DOC production in the organic samples
were correlated with cellulose (positively) and lignin (negatively) proportion in the organic matter, whereas in the mineral
samples C and nitrogen (N) provided positive correlations. The partitioning of C released into CO2–C and DOC showed a quotient (CO2–C:DOC) that varied widely among the samples, from 1 to 146. The regression coefficient of CO2–C:DOC production (log10 transformed) ranged from 0.3 to 0.7, all significantly less than 1. At high rates of DOC production, a smaller proportion
of CO2 is produced. The CO2–C:DOC quotient was dependent on incubation temperature: in the organic soil samples, the CO2–C:DOC quotient rose from an average of 6 at 3 to 16 at 22°C and in the mineral samples the rise was from 7 to 27. The CO2–C:DOC quotient was related to soil pH in the organic samples and C and N forms in the mineral samples. 相似文献
2.
3.
The objective of this study was to improve the biological water–gas shift reaction for producing hydrogen (H2) by conversion of carbon monoxide (CO) using an anaerobic thermophilic pure strain, Carboxydothermus hydrogenoformans. Specific hydrogen production rates and yields were investigated at initial biomass densities varying from 5 to 20 mg volatile
suspended solid (VSS) L−1. Results showed that the gas–liquid mass transfer limits the CO conversion rate at high biomass concentrations. At 100-rpm
agitation and at CO partial pressure of 1 atm, the optimal substrate/biomass ratio must exceed 5 mol CO g−1 biomass VSS in order to avoid gas–liquid substrate transfer limitation. An average H2 yield of 94 ± 3% and a specific hydrogen production rate of ca. 3 mol g−1 VSS day−1 were obtained at initial biomass densities between 5 and 8 mg VSS−1. In addition, CO bioconversion kinetics was assessed at CO partial pressure from 0.16 to 2 atm, corresponding to a dissolved
CO concentration at 70°C from 0.09 to 1.1 mM. Specific bioactivity was maximal at 3.5 mol CO g−1 VSS day−1 for a dissolved CO concentration of 0.55 mM in the culture. This optimal concentration is higher than with most other hydrogenogenic
carboxydotrophic species. 相似文献
4.
Jana Woelfel Rhena Schumann Florian Peine Anita Flohr Aleksandra Kruss Jaroslaw Tegowski Philippe Blondel Christian Wiencke Ulf Karsten 《Polar Biology》2010,33(9):1239-1253
During summer 2007, Arctic microphytobenthic potential primary production was measured at several stations around the coastline
of Kongsfjorden (Svalbard, Norway) at ≤5 m water depth and at two stations at five different water depths (5, 10, 15, 20,
30 m). Oxygen planar optode sensor spots were used ex situ to determine oxygen exchange in the overlying water of intact sediment
cores under controlled light (ca. 100 μmol photons m−2 s−1) and temperature (2–4°C) conditions. Patches of microalgae (mainly diatoms) covering sandy sediments at water depths down
to 30 m showed high biomass of up to 317 mg chl a m−2. In spite of increasing water depth, no significant trend in “photoautotrophic active biomass” (chl a, ratio living/dead cells, cell sizes) and, thus, in primary production was measured at both stations. All sites from ≤5 to
30 m water depth exhibited variable rates of net production from −19 to +40 mg O2 m−2 h−1 (−168 to +360 mg C m−2 day−1) and gross production of about 2–62 mg O2 m−2 h−1 (17–554 mg C m−2 day−1), which is comparable to other polar as well as temperate regions. No relation between photoautotrophic biomass and gross/net
production values was found. Microphytobenthos demonstrated significant rates of primary production that is comparable to
pelagic production of Kongsfjorden and, hence, emphasised the importance as C source for the zoobenthos. 相似文献
5.
Calcification and primary production responses to irradiance in the temperate coralline alga Lithothamnion corallioides were measured in summer 2004 and winter 2005 in the Bay of Brest. Coralline algae were incubated in dark and clear bottles exposed to different irradiances. Net primary production reached 1.5 μmol C g−1 dry wt h−1 in August and was twice as high as in January–February. Dark respiration showed significant seasonal variations, being three-fold higher in summer. Maximum calcification varied from 0.6 μmol g−1 dry wt h−1 in summer 2004 to 0.4 μmol g−1 dry wt h−1 in winter 2005. According to P–E curves and the daily course of irradiance, estimated daily net production and calcification reached 131 μg C g−1 dry wt and 970 μg CaCO3 g−1 dry wt in summer 2004, and 36 μg C g−1 dry wt and 336 μg CaCO3 g−1 dry wt in winter 2005. The net primary production of natural L. corallioides populations in shallow waters was estimated at 10–600 g C m−2 y−1, depending on depth and algal biomass. The mean annual calcification of L. corallioides populations varied from 300 to 3000 g CaCO3 m−2. These results are similar to those reported for tropical coralline algae in terms of carbon and carbonate productivity. Therefore, L. corallioides can be considered as a key element of carbon and carbonate cycles in the shallow coastal waters where they live. 相似文献
6.
Daria M. Martynova Natalia A. Kazus Ulrich V. Bathmann Martin Graeve Alexey A. Sukhotin 《Polar Biology》2011,34(8):1175-1195
We have studied the seasonal dynamics of abundance and feeding characteristics of three species of calanoid copepods (Acartia spp., Centropages hamatus and Temora longicornis) in the White Sea from the surface water layer (0–10 m), in order to assess their role in the pelagic food web and to determine
the major factors governing their population dynamics during the productive season. These species dominated in the upper water
layer (0–10 m) from June through September, producing up to 3 generations per year. Data on the food spectra revealed all
species to be omnivorous; but some inter- and intraspecific differences were observed. Generally, copepods consumed diatoms,
dinoflagellates and microzooplankton. The omnivory index ‘UC’ (i.e., fatty acid unsaturation coefficient) varied from 0.2
to 0.6, which implied ingestion of phytoplankton. The different degree of selectivity on the same food items by the studied
species was observed, and therefore, successful surviving strategy with minimal overlapping could be assumed. In total, the
populations of the three studied copepod species grazed up to 2.15 g C m−2 day−1 and released up to 0.68 g C m−2 day−1 in faecal pellets. They consumed up to 50% of particulate organic carbon, or up to 85% of phytoplankton standing stock (in
terms of Chl. a), and thus played a significant role in the transformation of particulate organic matter. Seasonal changes in abundance of
the studied species depended mostly on water temperature in the early summer, but were also affected by food availability
(Chl. a concentration) during the productive season. 相似文献
7.
Le Dinh Hung Kanji Hori Huynh Quang Nang Tran Kha Le Thi Hoa 《Journal of applied phycology》2009,21(3):265-272
The three color morphotypes of the red alga Kappaphycus alvarezii (brown, red and green) were cultured in Camranh Bay, Vietnam, using the fixed off-bottom monoline culture method to evaluate
the growth rate, carrageenan yield, 3,6-anhydrogalactose, gel strength and lectin content. The brown morphotype was cultivated
over a 12-month period; the red and green morphotypes were over a 6-month period. At the 60-day culture timepoint, the brown
morphotype showed a higher growth rate (3.5–4.6% day−1) from September to February, and lower growth rate (1.6–2.8% day−1) from March to August. Significant (P < 0.05) differences in growth rate between culture months were found with the brown morphotype. High growth rates for the
red (3.6–4.4% day−1) and green (3.7–4.2% day−1) morphotypes were obtained from September to February. The carrageenan yield, 3,6-anhydrogalactose and gel strength of the
three morphotypes showed little variation, with the highest values obtained in November–December. At the 30-day sampling point,
the brown morphotype had a higher lectin content (167–302 μg g−1 dry alga) from August to March and a lower lectin content (23–104 μg g−1 dry alga) from April to July. High lectin contents were recorded for the red (139–338 μg g−1 dry alga) and green (124–259 μg g−1 dry alga) morphotypes from September to February. This study shows that the different morphotypes of K. alvarezii can be grown in the tropical waters of the Camranh during the northeast monsoon, and part of the southwest monsoon, especially
the brown morphotype, which can be grown during any season. 相似文献
8.
We compared on eight dates during the ice-free period physicochemical properties and rates of phytoplankton and epipelic primary
production in six arctic lakes dominated by soft bottom substrate. Lakes were classified as shallow ( < 2.5 m), intermediate in depth (2.5 m < < 4.5 m), and deep ( > 4.5 m), with each depth category represented by two lakes. Although shallow lakes circulated freely and intermediate and
deep lakes stratified thermally for the entire summer, dissolved oxygen concentrations were always >70% of saturation values.
Soluble reactive phosphorus and dissolved inorganic nitrogen (DIN = NO3
−–N + NH4
+–N) were consistently below the detection limit (0.05 μmol l−1) in five lakes. However, one lake shallow lake (GTH 99) periodically showed elevated values of DIN (17 μmol l−1), total-P (0.29 μmol l−1), and total-N (33 μmol l−1), suggesting wind-generated sediment resuspension. Due to increased nutrient availability or entrainment of microphytobenthos,
GTH 99 showed the highest average volume-based values of phytoplankton chlorophyll a (chl a) and primary production, which for the six lakes ranged from 1.0 to 2.9 μg l−1 and 0.7–3.8 μmol C l−1 day−1. Overall, however, increased resulted in increased area-based values of phytoplankton chl a and primary production, with mean values for the three lake classes ranging from 3.6 to 6.1 mg chl a m−2 and 3.2–5.8 mmol C m−2 day−1. Average values of epipelic chl a ranged from 131 to 549 mg m−2 for the three depth classes, but levels were not significantly different due to high spatial variability. However, average
epipelic primary production was significantly higher in shallow lakes (12.2 mmol C m−2 day−1) than in intermediate and deep lakes (3.4 and 2.4 mmol C m−2 day−1). Total primary production (6.7–15.4 mmol C m−2 day−1) and percent contribution of the epipelon (31–66%) were inversely related to mean depth, such that values for both variables
were significantly higher in shallow lakes than in intermediate or deep lakes.
Handling editor: L. Naselli-Flores 相似文献
9.
Altitudinal changes in carbon storage of temperate forests on Mt Changbai, Northeast China 总被引:8,自引:0,他引:8
Biao Zhu Xiangping Wang Jingyun Fang Shilong Piao Haihua Shen Shuqing Zhao Changhui Peng 《Journal of plant research》2010,123(4):439-452
A number of studies have investigated regional and continental scale patterns of carbon (C) stocks in forest ecosystems; however,
the altitudinal changes in C storage in different components (vegetation, detritus, and soil) of forest ecosystems remain
poorly understood. In this study, we measured C stocks of vegetation, detritus, and soil of 22 forest plots along an altitudinal
gradient of 700–2,000 m to quantify altitudinal changes in carbon storage of major forest ecosystems (Pinus koraiensis and broadleaf mixed forest, 700–1,100 m; Picea and Abies forest, 1,100–1,800 m; and Betula ermanii forest, 1,800–2,000 m) on Mt Changbai, Northeast China. Total ecosystem C density (carbon stock per hectare) averaged 237 t C ha−1 (ranging from 112 to 338 t C ha−1) across all the forest stands, of which 153 t C ha−1 (52–245 t C ha−1) was stored in vegetation biomass, 14 t C ha−1 (2.2–48 t C ha−1) in forest detritus (including standing dead trees, fallen trees, and floor material), and 70 t C ha−1 (35–113 t C ha−1) in soil organic matter (1-m depth). Among all the forest types, the lowest vegetation and total C density but the highest
soil organic carbon (SOC) density occurred in Betula ermanii forest, whereas the highest detritus C density was observed in Picea and Abies forest. The C density of the three ecosystem components showed distinct altitudinal patterns: with increasing altitude, vegetation
C density decreased significantly, detritus C density first increased and then decreased, and SOC density exhibited increasing
but insignificant trends. The allocation of total ecosystem C to each component exhibited similar but more significant trends
along the altitudinal gradient. Our results suggest that carbon storage and partitioning among different components in temperate
forests on Mt Changbai vary greatly with forest type and altitude. 相似文献
10.
This study focuses on selective feeding by developmental stages of two oceanic copepods, Calanus finmarchicus and Calanus helgolandicus from nauplii to adults. A mixture of four algal species of different biochemical composition, Prorocentrum nanum (dinoflagellate), Thalassiosira minima (diatom), Rhodomonas baltica (cryptophyte) and Dunaliella tertiolecta (chlorophyte), added in an equal biovolume, was used in three different experimental set-ups. In set-up 1 the algal species
were present as single cells of similar size (14 μm). In set-up 2 the diatom T. minima was present in chains of two or three cells and was therefore larger than the other algae, while the biovolume of all species
remained the same. In set-up 3, the diatom T. minima was excluded from the mixture. Feeding selectivity of the copepods was assessed in relation to the quality of the algal species
expressed in terms of carbon and nitrogen content, fatty acid composition, and chain length of the diatom. The results show
that younger stages and adult females of C. finmarchicus and C. helgolandicus did not show a preference for an algal species when the algae were of similar size. In the feeding experiments where the
diatoms were offered as chains, both copepod species showed a selective behaviour only on the basis of algal size. Individual
ingestion rates increased from 0.4 to 0.7 μg C day–1 for nauplii of both species to 5 μg C day–1 for adult females of C. helgolandicus to 12 μg C day–1 for C. finmarchicus. Individual filtration rates ranged from 5 ml day–1 for C. finmarchicus nauplii to 70–98 ml day–1 for adult females, and from 3 ml day–1 for C. helgolandicus nauplii to 35–46 ml day–1 for adult females. Ingestion and filtration rates per unit body carbon decreased gradually in both copepod species with increasing
body carbon. The daily ingested amount of food decreased for C. finmarchicus from 124–134% of the body carbon for nauplii to 19% of the body carbon for adult females, and for C. helgolandicus from 117–137% of the body carbon for nauplii to 13–26% of the body carbon of adult females.
Electronic Publication 相似文献
11.
Biological breakdown of denitrifying sulfide removal process in high-rate expanded granular bed reactor 总被引:1,自引:0,他引:1
This work conducted a denitrifying sulfide removal (DSR) test in an expanded granular sludge bed (EGSB) reactor at sustainable
loadings of 6.09 kg m−3 day−1 for sulfide, 3.11 kg m−3 day−1 for nitrate–nitrogen, and 3.27 kg m−1 day−1 for acetate–carbon with >93% efficiency, which is significantly higher than those reported in literature. Strains Pseudomonas sp., Nitrincola sp., and Azoarcus sp. very likely yield heterotrophs. Strains Thermothrix sp. and Sulfurovum sp. are the autotrophs required for the proposed high-rate EGSB-DSR system. The EGSB-DSR reactor experienced two biological
breakdowns, one at loadings of 4.87, 2.13, and 1.82 kg m−3 day−1; reactor function was restored by increasing nitrate and acetate loadings. Another breakdown occurred at loadings of up to
8.00, 4.08, and 4.50 kg m−1 day−1; the heterotrophic denitrification pathway declined faster than the autotrophic pathway. The mechanism of DSR breakdown is
as follows. High sulfide concentration inhibits heterotrophic denitrifiers, and the system therefore accumulates nitrite.
Autotrophic denitrifiers are then inhibited by the accumulated nitrite, thereby leading to breakdown of the DSR process. 相似文献
12.
Chaetognaths are among the most abundant predators in the Southern Ocean and are potentially important components in the biological
carbon pump due to the production of large, fast-sinking fecal pellets. In situ S. gazellae abundance, fecal pellet production, sinking rates, carbon content, and vertical carbon fluxes were measured at the Lazarev Sea between
December 2005 and January 2006. Sagitta gazellae produce fecal pellets that sink at speeds of 33–600 m day−1 and have carbon contents of 0.01–0.8 mg C pellet−1. Vertical carbon flux was later compared with the total carbon flux measured at 360 m depth at the study area. Rough estimates
using published seasonal abundance of S. gazellae indicate that, at 360 m depth in the Lazarev Sea, this specie may contribute 12 and 5% of the total vertical carbon flux
in winter (ice-covered) and summer (ice-free), respectively. Thus, the role of chaetognaths in the downward transport of organic
matter may be far more important than previously thought. 相似文献
13.
Han Gil Choi Ki Hoon Lee Hyun Il Yoo Pil Jun Kang Young Sik Kim Ki Wan Nam 《Journal of applied phycology》2008,20(5):729-735
The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature–irradiance
(10, 15, 20, 25, 30°C × 20, 40, 80 μmol photons m−2s−1) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10–25°C), irradiances (20–80 μmol photons m−2s−1), and daylengths (8–24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day−1 (25°C, 20 μmol photons m−2s−1) and 13% day−1 (8 h daylength). In contrast, the RGRs of the blade weights were 4% day−1 (15°C, 20 μmol photons m−2s−1) and 5% day−1 (12 h daylength). Negative growth rates were found at 20 μmol photons m−2s−1 of 20°C and 25°C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25°C, 20 μmol photons m−2s−1, and 8 h daylength for construction of Sargassum beds and restoration of barren areas. 相似文献
14.
Sunil S. Adav Duu-Jong Lee Juin-Yih Lai 《Applied microbiology and biotechnology》2010,85(5):1601-1610
Aerobic sludge granules are compact, strong microbial aggregates that have excellent settling ability and capability to efficiently
treat high-strength and toxic wastewaters. Aerobic granules disintegrate under high organic loading rates (OLR). This study
cultivated aerobic granules using acetate as the sole carbon and energy source in three identical sequencing batch reactors
operated under OLR of 9–21.3 kg chemical oxygen demand (COD) m−3 day−1. The cultivated granules removed 94–96% of fed COD at OLR up to 9–19.5 kg COD m−3 day−1, and disintegrated at OLR of 21.3 kg COD m−3 day−1. Most tested isolates did not grow in the medium at >3,000 mg COD l−1; additionally, these strains lost capability for auto-aggregation and protein or polysaccharide productivity. This critical
COD regime correlates strongly with the OLR range in which granules started disintegrating. Reduced protein quantity secreted
by isolates was associated with the noted poor granule integrity under high OLR. This work identified a potential cause of
biological nature for aerobic granules breakdown. 相似文献
15.
Sánchez Fernández JF González-López CV Acién Fernández FG Fernández Sevilla JM Molina Grima E 《Applied microbiology and biotechnology》2012,94(3):613-624
This paper focuses on modelling the growth rate and exopolysaccharides production of Anabaena sp. ATCC 33047, to be used in carbon dioxide removal and biofuels production. For this, the influence of dilution rate, irradiance
and aeration rate on the biomass and exopolysaccharides productivity, as well as on the CO2 fixation rate, have been studied. The productivity of the cultures was maximum at the highest irradiance and dilution rate
assayed, resulting to 0.5 gbio l−1 day−1 and 0.2 geps l−1 day−1, and the CO2 fixation rate measured was 1.0 gCO2 l−1 day−1. The results showed that although Anabaena sp. was partially photo-inhibited at irradiances higher than 1,300 μE m−2 s−1, its growth rate increases hyperbolically with the average irradiance inside the culture, and so does the specific exopolysaccharides
production rate. The latter, on the other hand, decreases under high external irradiances, indicating that the exopolysaccharides
metabolism hindered by photo-damage. Mathematical models that consider these phenomena have been proposed. Regarding aeration,
the yield of the cultures decreased at rates over 0.5 v/v/min or when shear rates were higher than 60 s−1, demonstrating the existence of thus existence of stress damage by aeration. The behaviour of the cultures has been verified
outdoors in a pilot-scale airlift tubular photobioreactor. From this study it is concluded that Anabaena sp. is highly recommended to transform CO2 into valuable products as has been proved capable of metabolizing carbon dioxide at rates of 1.2 gCO2 l−1 day−1 outdoors. The adequacy of the proposed equations is demonstrated, resulting to a useful tool in the design and operation
of photobioreactors using this strain. 相似文献
16.
Macrophyte presence is an indicator of enhanced denitrification and nitrification in sediments of a temperate restored agricultural stream 总被引:1,自引:0,他引:1
Stream macrophytes are often removed with their sediments to deepen stream channels, stabilize channel banks, or provide habitat
for target species. These sediments may support enhanced nitrogen processing. To evaluate sediment nitrogen processing, identify
seasonal patterns, and assess sediment processes relative to stream load, we measured denitrification and nitrification rates
in a restored third- to fourth-order agricultural stream, Black Earth Creek, Wisconsin, and estimated processing over a 10 km
reach. Our results show that sediments with submerged and emergent macrophytes (e.g., Potomageton spp. and Phalaris arudinacea) support greater denitrification rates than bare sediments (1.12 μmol N g−1 h−1 vs. 0.29). Sediments with macrophytes were not carbon limited and organic matter fraction was weakly correlated to denitrification.
The highest denitrification potential occurred in macrophyte beds (5.19 μmol N g−1 h−1). Nitrification rates were greater in emergent beds than bare sediments (1.07 μg N ml−1day−1 vs. 0.35) with the greatest nitrification rates during the summer. Total denitrification removal in sediments with macrophytes
was equivalent to 43% of the nitrate stream load (463.7 kg N day−1) during spring and nitrification in sediments with macrophytes was equivalent to 247% of summer ammonium load (3.5 kg N day−1). Although the in-channel connectivity to nitrogen rich water was limited, actual stream nitrogen loads could increase with
removal of macrophytes. Macrophyte beds and supporting fringing wetted areas are important if nitrogen management is a concern
for riparian stream restoration efforts. 相似文献
17.
Shannon KE Saleh-Lakha S Burton DL Zebarth BJ Goyer C Trevors JT 《Antonie van Leeuwenhoek》2011,100(2):183-195
The effect of glucose addition (0 and 500 μg C g−1 soil) and nitrate (NO3) addition (0, 10, 50 and 500 μg NO3–N g−1 soil) on nitric oxide reductase (cnorB) gene abundance and mRNA levels, and cumulative denitrification were quantified over 48 h in anoxic soils inoculated with
Pseudomonas mandelii. Addition of glucose-C significantly increased cnorB
p
(P. mandelii and related species) mRNA levels and abundance compared with soil with no glucose added, averaged over time and NO3 addition treatments. Without glucose addition, cnorB
p
mRNA levels were higher when 500 μg NO3–N g−1 soil was added compared with other NO3 additions. In treatments with glucose added, addition of 50 μg NO3–N g−1 soil resulted in higher cnorB
p
mRNA levels than soil without NO3 but was not different from the 10 and 500 μg NO3–N g−1 treatments. cnorB
p
abundance in soils without glucose addition was significantly higher in soils with 500 μg NO3–N g−1 soil compared to lower N-treated soils. Conversely, addition of 500 μg NO3–N g−1 soil resulted in lower cnorB
p
abundance compared with soil without N-addition. Over 48 h, cumulative denitrification in soils with 500 μg glucose-C g−1 soil, and 50 or 500 μg NO3–N g−1 was higher than all other treatments. There was a positive correlation between cnorB
p
abundance and cumulative denitrification, but only in soils without glucose addition. Glucose-treated soils generally had
higher cnorB
p
abundance and mRNA levels than soils without glucose added, however response of cnorB
p
abundance and mRNA levels to NO3 supply depended on carbon availability. 相似文献
18.
We examined the hydrologic controls on nitrogen biogeochemistry in the hyporheic zone of the Tanana River, a glacially-fed
river, in interior Alaska. We measured hyporheic solute concentrations, gas partial pressures, water table height, and flow
rates along subsurface flowpaths on two islands for three summers. Denitrification was quantified using an in situ 15NO3− push–pull technique. Hyporheic water level responded rapidly to change in river stage, with the sites flooding periodically
in mid−July to early−August. Nitrate concentration was nearly 3-fold greater in river (ca. 100 μg NO3−–N l−1) than hyporheic water (ca. 38 μg NO3−–N l−1), but approximately 60–80% of river nitrate was removed during the first 50 m of hyporheic flowpath. Denitrification during
high river stage ranged from 1.9 to 29.4 mg N kg sediment−1 day−1. Hotspots of methane partial pressure, averaging 50,000 ppmv, occurred in densely vegetated sites in conjunction with mean
oxygen concentration below 0.5 mgO2 l−1. Hyporheic flow was an important mechanism of nitrogen supply to microbes and plant roots, transporting on average 0.41 gNO3−–N m−2 day−1, 0.22 g NH4+–N m−2 day−1, and 3.6 g DON m−2 day−1 through surface sediment (top 2 m). Our results suggest that denitrification can be a major sink for river nitrate in boreal
forest floodplain soils, particularly at the river-sediment interface. The stability of the river hydrograph and the resulting
duration of soil saturation are key factors regulating the redox environment and anaerobic metabolism in the hyporheic zone. 相似文献
19.
The zooxanthellate octocoral Sinularia flexibilis is a producer of potential pharmaceutically important metabolites such as antimicrobial and cytotoxic substances. Controlled
rearing of the coral, as an alternative for commercial exploitation of these compounds, requires the study of species-specific
growth requirements. In this study, phototrophic vs. heterotrophic daily energy demands of S. flexibilis was investigated through light and Artemia feeding trials in the laboratory. Rate of photosynthetic oxygen by zooxanthellae in light (≈200 μmol quanta m−2 s−1) was measured for the coral colonies with and without feeding on Artemia nauplii. Respiratory oxygen was measured in the dark, again with and without Artemia nauplii. Photosynthesis–irradiance curve at light intensities of 0, 50, 100, 200, and 400 μmol quanta m−2 s−1 showed an increase in photosynthetic oxygen production up to a light intensity between 100 and 200 μmol quanta m−2 s−1. The photosynthesis to respiration ratio (P/R > 1) confirmed phototrophy of S. flexibilis. Both fed and non-fed colonies in the light showed high carbon contribution by zooxanthellae to animal (host) respiration
values of 111–127%. Carbon energy equivalents allocated to the coral growth averaged 6–12% of total photosynthesis energy
(mg C g
−
1 buoyant weight day
−
1) and about 0.02% of the total daily radiant energy. “Light utilization efficiency (ε)” estimated an average ε value of 75%
12 h
−
1 for coral practical energetics. This study shows that besides a fundamental role of phototrophy vs. heterotrophy in daily
energy budget of S. flexibilis, an efficient fraction of irradiance is converted to useable energy. 相似文献
20.
Specific growth rates of heterotrophic bacterioplankton have been frequently estimated from in situ bacterial production (BP)
to biomass (BB) ratios, using a series of assumptions that may result in serious discrepancies with values obtained from predator-free
cultures. Here, we used both types of approaches together with a comprehensive assessment of single-cell physiological characteristics
(membrane integrity, nucleic acid content, and active respiration) of coastal bacterioplankton during a complete annual cycle
(February 2007–January 2008) in the southern Bay of Biscay off Xixón, Spain. Both leucine and thymidine incorporation rates
were used in conjunction with empirical tracer to carbon or cells conversion factors (eCFs) to accurately derive BP. Leu and
TdR incorporation rates covaried year-round, as did the corresponding eCFs at 0 and 50 m depth. eCFs peaked in autumn, with
mean annual values close to the theoretical ones (3.4 kg C mol Leu−1 and 2.0 × 1018 cells mol TdR−1). Bacterial abundance (0.2–1.5 × 106 cells L−1) showed a bimodal distribution with maxima in May and October and minima in March. Live (membrane-intact) cells dominated
year-round (79–97%), with high nucleic acid cells (42–88%) and actively respiring bacteria (CTC+, 1–16%) showing distinct
surface maxima in April and July, respectively. BB (557–1,558 mg C m−2) and BP (7–139 mg C m−2 day−1) presented two distinct peaks in spring and autumn, both of similar size due to a strong upwelling event observed in September.
Specific growth rates (0.35–3.8 day−1) were one order of magnitude higher in predator-free incubations than bacterial turnover rates derived from integrated BP:BB
ratios (0.01–0.16 and 0.01–0.09 day−1, for Leu and TdR, respectively) and were not correlated, probably due to a significant contribution of low activity cells
to total standing stocks. The Leu:TdR molar ratio averaged for the water column (6.6–25.5) decreased significantly with higher
integrated BB, indicating that low standing stocks tend to present unbalanced growth. Discrepancies about the true magnitude
of specific growth rates must be solved before fully appreciating the role of bacteria in the ocean carbon cycle. 相似文献