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1.
We investigated the ability of Enteromorpha intestinalis (L.) Link to take up pulses of different species of nitrogen simultaneously, as this would be an important mechanism to enhance bloom ability in estuaries. Uptake rates and preference for NH4+ or NO3− following 1, 3, 6, 9, 12 or 24 h of exposure to either 15NH4NO3 or NH415NO3 were determined by disappearance of N from the medium. Differences in assimilation rates for NH4+ or NO3− were quantified by the accumulation of NH4+, NO3−, and atom % 15N in the algal tissue. NH4+ concentration was reduced more quickly than water NO3− concentration. Water column NH4+ concentration after the longest time interval was reduced from 300 to 50 μM. Water NO3− was reduced from 300 to 150 μM. The presence of 15N or 14N had no effect on uptake of either NH4+ or NO3−. 15N was removed from the water at an almost identical rate and magnitude as 14N. Differences in accumulation of 15NH4+ and 15NO3− in the tissue reflected disappearance from the water; 15N from NH4+ accumulated faster and reached an atom % twice that of 15N from NO3−. This outcome suggested that when NH4+ and NO3− were supplied in equal concentrations, more NH4+ was taken up and assimilated. The ability to take up high concentrations of NH4+, and NO3− simultaneously is important for bloom-forming species of estuarine macroalgae subject to multiple nutrient species from various sources. 相似文献
2.
H.Allen Southerland 《Journal of experimental marine biology and ecology》2004,298(2):303-322
Polycyclic aromatic hydrocarbons (PAHs) are common pollutants associated with urbanization and suburbanization in estuarine systems, but little is known about their effects on the physiological properties of microalgae. We examined the effects of ultraviolet (UV)-activated fluoranthene toxicity on (a) the growth, chlorophyll a content cell−1, and pigment composition of axenic Ankistrodesmus sp. (an estuarine benthic green microalga) and (b) the phytoplankton population growth and pigment composition of natural communities from an urbanized (Murrells Inlet) vs. forested (North Inlet) salt marsh estuary. The zeaxanthin/violaxanthin ratio increased in Ankistrodesmus sp. cultures exposed to UV light in the presence of fluoranthene, supporting the hypothesis that xanthophyll cycling is an energy dissipative response to photoinduced PAH toxicity in this species. Exposure of natural communities to the combination of UV light and fluoranthene resulted in decreased chlorophyll production and increased zeaxanthin violaxanthin−1 in samples from the urbanized estuary (Murrells Inlet), but not North Inlet, suggesting that phytoplankton in the former “fluoranthene-impacted” estuary were more susceptible to fluoranthene toxicity. Consideration of xanthophyll cycling as a microalgal response to UV-activated PAH toxicity has implications to understanding the influence of these contaminants on microbial food web structure and ecosystem production. 相似文献
3.
D Burdloff S GaspariniF Villate I UriarteU Cotano B SautourH Etcheber 《Journal of experimental marine biology and ecology》2002,274(1):1-17
The egg production of the copepod Acartia bifilosa was measured and related to environmental variables and food availability in two estuaries located in the same biogeographic region (Bay of Biscay) but showing very strong differences in abiotic and biotic features: the Gironde estuary (France) and the estuary of Mundaka (Spain). The study was conducted during the spring-summer-autumn period of 1994. Food availability was evaluated by analysing the chlorophyll a (Chl a), the particulate organic carbon (POC) and the easily extractable macromolecular compounds such as proteins, carbohydrates and lipids of the seston. The egg production of copepods was estimated from field incubations with natural water, and phytoplankton feeding of adult females was estimated by means of the gut fluorescence method. The nutritional environment of the Gironde was characterised by high amounts of suspended particulate matter (SPM) with low food value, emphasising the mainly detrital origin of the organic matter (OM). In Mundaka, the higher contribution of phytoplankton to the seston led to marked increases in particulate food value accounting for up to 35% of organic matter. The weight-specific egg production was found to be sharply higher in Mundaka (ranging from 0.2 to 0.63×10−3 day−1) than in the Gironde (ranging from 0 to 0.13×10−3 day−1), but the seasonal trend of variations was similar, the highest weight-specific egg production rates occurring in early summer and the lowest in autumn in both estuaries. Egg production was not correlated linearly with temperature since maximal egg production occurred at intermediate temperatures. In Mundaka, the egg production showed a significant positive correlation with the chlorophyll and the Chl/SPM and the POC/SPM ratios. This coupled with higher values of algal food availability (Chl a/SPM: 10 to 1870 μg g−1) and gut fluorescence (between 0.12 and 0.38 ng Chl a Eq ind−1) indicate that a herbivorous diet could cover the energy requirements of A. bifilosa and support egg production. In the Gironde, the algal food availability and the gut fluorescence were lower (Chl a/SPM: 10 to 80 μg g−1; GF: 0.09 and 0.25 ng Chl a Eq ind−1), and the egg production showed significant positive correlation with the particulate food value, suggesting that other sources of carbon rather than phytoplankton were responsible for the observed changes in egg production. Results indicate that the particular seston properties of each system may be responsible for the noticeable differences in A. bifilosa fertility among estuaries. 相似文献
4.
In this study we assessed the growth, morphological responses, and N uptake kinetics of Salvinia natans when supplied with nitrogen as NO3−, NH4+, or both at equimolar concentrations (500 μM). Plants supplied with only NO3− had lower growth rates (0.17 ± 0.01 g g−1 d−1), shorter roots, smaller leaves with less chlorophyll than plants supplied with NH4+ alone or in combination with NO3− (RGR = 0.28 ± 0.01 g g−1 d−1). Ammonium was the preferred form of N taken up. The maximal rate of NH4+ uptake (Vmax) was 6–14 times higher than the maximal uptake rate of NO3− and the minimum concentration for uptake (Cmin) was lower for NH4+ than for NO3−. Plants supplied with NO3− had elevated nitrate reductase activity (NRA) particularly in the roots showing that NO3− was primarily reduced in the roots, but NRA levels were generally low (<4 μmol NO2− g−1 DW h−1). Under natural growth conditions NH4+ is probably the main N source for S. natans, but plants probably also exploit NO3− when NH4+ concentrations are low. This is suggested based on the observation that the plants maintain high NRA in the roots at relatively high NH4+ levels in the water, even though the uptake capacity for NO3− is reduced under these conditions. 相似文献
5.
The effects of inorganic nitrogen (N) source (NH4+, NO3− or both) on growth, biomass allocation, photosynthesis, N uptake rate, nitrate reductase activity and mineral composition of Canna indica were studied in hydroponic culture. The relative growth rates (0.05-0.06 g g−1 d−1), biomass allocation and plant morphology of C. indica were indifferent to N nutrition. However, NH4+ fed plants had higher concentrations of N in the tissues, lower concentrations of mineral cations and higher contents of chlorophylls in the leaves compared to NO3− fed plants suggesting a slight advantage of NH4+ nutrition. The NO3− fed plants had lower light-saturated rates of photosynthesis (22.5 μmol m−2 s−1) than NH4+ and NH4+/NO3− fed plants (24.4-25.6 μmol m−2 s−1) when expressed per unit leaf area, but similar rates when expressed on a chlorophyll basis. Maximum uptake rates (Vmax) of NO3− did not differ between treatments (24-35 μmol N g−1 root DW h−1), but Vmax for NH4+ was highest in NH4+ fed plants (81 μmol N g−1 root DW h−1), intermediate in the NH4NO3 fed plants (52 μmol N g−1 root DW h−1), and lowest in the NO3− fed plants (28 μmol N g−1 root DW h−1). Nitrate reductase activity (NRA) was highest in leaves and was induced by NO3− in the culture solutions corresponding to the pattern seen in fast growing terrestrial species. Plants fed with only NO3− had high NRA (22 and 8 μmol NO2− g−1 DW h−1 in leaves and roots, respectively) whereas NRA in NH4+ fed plants was close to zero. Plants supplied with both forms of N had intermediate NRA suggesting that C. indica takes up and assimilate NO3− in the presence of NH4+. Our results show that C. indica is relatively indifferent to inorganic N source, which together with its high growth rate contributes to explain the occurrence of this species in flooded wetland soils as well as on terrestrial soils. Furthermore, it is concluded that C. indica is suitable for use in different types of constructed wetlands. 相似文献
6.
Clavery Tungaraza Véronique Rousseau Christiane Lancelot Willy Baeyens 《Journal of experimental marine biology and ecology》2003,292(1):19-41
This paper documents ambient concentrations of nutrients in the Belgian coastal waters of the North Sea during the spring of 1996 and 1997. The paper elaborates the differences of uptake rates of oxidised nitrogen (NO3−) and reduced nitrogen (NH4 and urea) by Phaeocystis and diatoms. The nitrogen concentrations were dominated by NO3− with a maximum concentration of 30 μM (January 1997) and 40 μM (March 1996). In 1996, Phaeocystis dominated the spring biomass with a maximum of 521 μg C l−1, while maximum diatom biomass was 174 μg C l−1. In 1997, the maximum Phaeocystis spring biomass was 1600 μg C l−1 and diatom maximum biomass was below 100 μg C l−1. A maximum bacteria biomass of about 55 μg C l−1 was observed in mid-May 1996. The maximum nitrogen uptake rates were recorded during spring and were dominated by NO3− (0.005 h−1 in 1996 and 0.032 h−1 in 1997). Maximum specific NH4 uptake rates were between 0.005 h−1 in May 1996 and 0.006 h−1 in April 1997. The NO3− uptake rates displayed exponential decrease versus increasing ambient reduced nitrogen concentrations (ammonium and urea), whereas the reduced nitrogen uptake increased but never compensated the decreased nitrate uptake. The NH4 uptake kinetics of diatoms displayed lower vmax compared to Phaeocystis. Consequently, Phaeocystis showed ability to increase their NH4 uptake capacity when more NH4 became available while diatoms failed to do so, after ammonium had exceeded their saturation concentration (>1 μM). Although reduced nitrogen has a negative effect on the uptake of NO3−, Phaeocystis have more advantage than diatoms on the uptake of ammonium. This might be contributing to the biomass domination shown by Phaeocystis over extended periods in spring. 相似文献
7.
Nitrate (NO3−) and ammonium (NH4+) are the main forms of nitrogen available in the soil for plants. Excessive NH4+ accumulation in tissues is toxic for plants and exclusive NH4+-based nutrition enhances this effect. Ammonium toxicity syndrome commonly includes growth impairment, ion imbalance and chlorosis among others. In this work, we observed high intraspecific variability in chlorophyll content in 47 Arabidopsis thaliana natural accessions grown under 1 mM NH4+ or 1 mM NO3− as N-source. Interestingly, chlorophyll content increased in every accession upon ammonium nutrition. Moreover, this increase was independent of ammonium tolerance capacity. Thus, chlorosis seems to be an exclusive effect of severe ammonium toxicity while mild ammonium stress induces chlorophyll accumulation. 相似文献
8.
Maria H. Abreu R. Pereira I. Sousa-Pinto C. Yarish 《Journal of experimental marine biology and ecology》2011,407(2):190-199
The ammonium (NH4+) and nitrate (NO3−) uptake responses of tetrasporophyte cultures from a Portuguese population of Gracilaria vermiculophylla were studied. Thalli were incubated at 5 nitrogen (N) levels, including single (50 μM of NH4+ or NO3−) and combined addition of each of the N sources. For the combined additions, the experimental conditions attempted to simulate 2 environments with high N availability (450 μM NO3− + 150 μM NH4+; 250 μM NO3− + 50 μM NH4+) and the mean N concentrations occurring at the estuarine environment of this population (30 μM NO3− + 5 μM NH4+). The uptake kinetics of NH4+ and NO3− were determined during a 4 h time-course experiment with N deprived algae. The experiment was continued up to 48 h, with media exchanges every 4 h. The uptake rates and efficiency of the two N sources were calculated for each time interval. For the first 4 h, G. vermiculophylla exhibited non-saturated uptake for both N sources even for the highest concentrations used. The uptake rates and efficiency calculated for that period (V0-4 h), respectively, increased and decreased with increasing substrate concentration. NO3− uptake rates were superior, ranging from 1.06 ± 0.1 to 9.65 ± 1.2 μM g(dw)−1 h−1, with efficiencies of 19% to 53%. NH4+ uptake rates were lower (0.32 ± 0.0 to 5.75 ± 0.08 μM g(dw)−1 h−1) but G. vermiculophylla removed 63% of the initial 150 μM and 100% at all other conditions. Uptake performance of both N sources decreased throughout the duration of the experiment and with N tissue accumulation. Both N sources were taken up during dark periods though with better results for NH4+. Gracilaria vermiculophylla was unable to take up NO3− at the highest concentration but compensated with a constant 27% NH4+ uptake through light and dark periods. N tissue accumulation was maximal at the highest N concentration (3.9 ± 0.25% dw) and superior under NH4+ (3.57 ± 0.2% dw) vs NO3 (3.06 ± 0.1% dw) enrichment. The successful proliferation of G. vermiculophylla in estuarine environments and its potential utilization as the biofilter component of Integrated Multi-Trophic Aquaculture (IMTA) are discussed. 相似文献
9.
Instability of the turbidity maximum in the macrotidal Geum River estuary, western Korea 总被引:2,自引:0,他引:2
In the low-salinity area of many macrotidal estuaries, through the combination of tidal pumping and estuarine circulation,
an estuarine turbidity maximum (ETM) develops providing favorable conditions for various organisms. To investigate ecological
roles of the ETM in East Asian estuaries, we conducted seasonal observations in the Geum (or Keum) River estuary, one of the
representative macrotidal estuaries flowing into the Yellow Sea, from 2007 to 2008. The estuary was frequently filled with
high-salinity (>10 PSU) and low-turbidity (<100 NTU) water under small or no freshwater discharge from a dam (ca. 8 km upstream
from the river mouth). Brackish water was, however, completely pushed out of the estuary within a few hours after an intensive
discharge in summer. Chlorophyll a (up to 50 μg l−1) and pheophytin (up to 80 μg l−1) were concentrated in a low-salinity (<1 PSU) and high-turbidity (up to 1000 NTU) area, indicating that the intensive discharge
transported both living phytoplankton and resuspended detritus into the area. In contrast, a phytoplankton bloom (chlorophyll
a, up to 100 μg l−1) was observed at low salinities under little discharge in winter. The present study demonstrated an absence of the ETM suitable
for estuarine-dependent organisms from the present Geum River estuary, indicating potential importance of adequate control
of freshwater discharge for the formation and maintenance of the ETM. 相似文献
10.
González-Blanco G Beristain-Cardoso R Cuervo-López F Cervantes FJ Gómez J 《Bioresource technology》2012,103(1):48-55
The metabolic capability of denitrifying sludge to oxidize ammonium and p-cresol was evaluated in batch cultures. Ammonium oxidation was studied in presence of nitrite and/or p-cresol by 55 h. At 50 mg/L NH4+-N and 76 mg/L NO2−-N, the substrates were consumed at 100% and 95%, respectively, being N2 the product. At 50 mg/L NH4+-N and 133 mg/L NO2−-N, the consumption efficiencies decreased to 96% and 70%, respectively. The increase in nitrite concentration affected the ammonium oxidation rate. Nonetheless, the N2 production rate did not change. In organotrophic denitrification, the p-cresol oxidation rate was slower than ammonium oxidation. In litho-organotrophic cultures, the p-cresol and ammonium oxidation rates were affected at 133 mg/L NO2−-N. Nonetheless, at 76 mg/L NO2−-N the denitrifying sludge oxidized ammonium and p-cresol, but at different rate. Finally, this is the first work reporting the simultaneous oxidation of ammonium and p-cresol with the production of N2 from denitrifying sludge. 相似文献
11.
Different sensitivity of Phragmites australis and Glyceria maxima to high availability of ammonium-N
The ability to cope with NH4+-N was studied in the littoral helophytes Phragmites australis and Glyceria maxima, species commonly occupying fertile habitats rich in NH4+ and often used in artificial wetlands. In the present study, Glyceria growth rate was reduced by 16% at 179 μM NH4+-N, and the biomass production was reduced by 47% at 3700 μM NH4+-N compared to NO3−-N. Similar responses were not found in Phragmites. The amounts (mg g−1 dry wt) of starch and total non-structural carbohydrates (TNC) in rhizomes were significantly lower in NH4+ (8.9; 12.2 starch; 20.1; 41.9 TNC) compared to NO3− treated plants (28.0; 15.6 starch; 58.5; 56.3 TNC) in Phragmites and Glyceria, respectively. In addition, Glyceria showed lower amounts (mg g−1 dry wt) of soluble sugars, TNC, K+, and Mg2+ in roots under NH4+ (5.6; 14.3; 20.6; 1.9) compared to NO3− nutrition (11.6; 19.9; 37.9; 2.9, for soluble sugars, TNC, K+, and Mg2+, respectively), while root internal levels of NH4+ and Ca2+ (0.29; 4.6 mg g−1 dry wt, mean of both treatments) were only slightly affected. In Phragmites, no changes in soluble sugars, TNC, Ca2+, K+, and Mg2+ contents of roots (7.3; 14.9; 5.1; 17.3; 2.6 mg g−1 dry wt, means of both treatments) were found in response to treatments. The results, therefore, indicate a more pronounced tolerance towards high NH4+ supply in Phragmites compared to Glyceria, although the former may be susceptible to starch exhaustion in NH4+-N nutrition. In contrast, Glyceria's ability to colonize fertile habitats rich in NH4+ is probably related to the avoidance strategy due to shallow rooting or to the previously described ability to cope with high NH4+ levels when P availability is high and NO3− is also provided. 相似文献
12.
Brian E. Lapointe Peter J. Barile William R. Matzie 《Journal of experimental marine biology and ecology》2004,308(1):23-58
Land-based nutrient pollution represents a significant human threat to coral reefs globally. We examined this phenomenon in shallow seagrass and coral reef communities between the Content Keys (southern Florida Bay) and Looe Key (south of Big Pine Key) in the Lower Florida Keys by quantifying the role of physical forcing (rainfall, wind, tides) and water management on mainland South Florida to nutrient enrichment and blooms of phytoplankton, macroalgae, and seagrass epiphytes. Initial studies (Phase I) in 1996 involved daily water quality sampling (prior to, during, and following physical forcing events) at three stations (AJ, an inshore area directly impacted by sewage discharges; PR, a nearshore patch reef located inshore of Hawk Channel; and LK, an offshore bank reef at Looe Key) to assess the spatial and temporal patterns in advection of land-based nutrients to the offshore reefs. Concentrations of dissolved inorganic nitrogen (DIN=NH4++NO3−+NO2−), soluble reactive phosphorus (SRP), and chlorophyll a increased at PR and LK following a wind event (∼15 knots, northeast) in mid-February. The highest DIN (mostly NH4+) and SRP concentrations of the entire study occurred at the inshore AJ during an extreme low tide in March. Following the onset of the wet season in May, mean NH4+ and chlorophyll a concentrations increased significantly to maximum seasonal values at PR and LK during summer; relatively low concentrations of NO3− and a low f-ratio (NO3−/NH4++NO3−) at all stations during summer do not support the hypothesis that the seasonal phytoplankton blooms resulted from upwelling of NO3−. A bloom of the seagrass epiphyte Cladosiphon occidentalis (phaeophyta) followed the onset of the rainy season and increased NH4+ concentrations at LK, resulting in very high epiphyte:blade ratios (∼3:1) on Thalassia testudinum. Biomass of macroalgae increased at all three stations from relatively low values (<50 g dry wt m−2) in winter and early spring to higher values (∼100-300 g dry wt m−2) typical of eutrophic seagrass meadows and coral reefs following the onset of the rainy season. The mean δ15N value of Laurencia intricata (rhodophyta) during 1996 at AJ (+4.7‰) was within the range reported for macroalgae growing on sewage nitrogen; lower values at the more offshore PR (+3.1‰) and LK (+2.9‰) were at the low end of the sewage range, indicating an offshore dilution of the sewage signal during the 1996 study. However, transient increases in δ15N of Cladophora catanata (chlorophtyta) from ~+2% to +5% at LK concurrent with elevated NH4+ concentrations following rain and/or wind events in May and July suggest episodic advection of sewage nitrogen to the offshore LK station. The Phase II study involved sampling of macroalgae for δ15N along a gradient from the Content Keys through Big Pine Key and offshore to LK in the summer wet season of 2000 and again in the drought of spring 2001. During the July 2000 sampling, macroalgae in nearshore waters around Big Pine Key had elevated δ15N values (~+4‰) characteristic of sewage enrichment; lower values (~+2‰) at LK were similar to values reported for macroalgae in upstream waters of western Florida Bay influenced by nitrogen-rich Everglades runoff. That pattern contrasted with the drought sampling in March 2001, when δ15N values of macroalgae were elevated (+6‰) to levels characteristic of sewage enrichment over a broad spatial scale from the Content Keys to LK. These results suggest that regional-scale agricultural runoff from the mainland Everglades watersheds as well as local sewage discharges from the Florida Keys are both significant nitrogen sources supporting eutrophication and algal blooms in seagrass and coral reef communities in the Lower Florida Keys. Hydrological and physical forcing mechanisms, including rainfall, water management on the South Florida mainland, wind, and tides, regulate the relative importance and variability of these anthropogenic nitrogen inputs over gradients extending to the offshore waters of the Florida Reef Tract. 相似文献
13.
Sweet flag (Acorus calamus L.) and yellow flag (Iris pseudacorus L.) have been used increasingly in constructed wetlands (CWs) for treatment of eutrophic wastewater. In order to properly match plant species with the type of wastewater being treated, it is important to know the performance of plant species under different NO3−/NH4+ ratios. We investigated dry matter (DW) production and N content of A. calamus and I. pseudacorus under five NO3−/NH4+ ratios (100/0, 75/25, 50/50, 25/75, and 0/100) in a hydroponic system. Results showed that the two species exhibited different preferences for NO3− and NH4+. Total DW, shoot DW, and N content were greater with NO3−/NH4+ ratios of 50/50 and 75/25 than otherwise for A. calamus, but these parameters were only higher under the sole NO3− treatment in I. pseudacorus. We conclude that A. calamus could be best used for treating wastewater in constructed wetlands with NO3−/NH4+ ratios between 50/50 and 75/25, while I. pseudacorus for treating wastewater with NO3− only to achieve the highest biomass production and efficiency in the removal of N. 相似文献
14.
Karin Karlson Rutger Rosenberg 《Journal of experimental marine biology and ecology》2007,344(2):123-135
This study focused on effects from Monoporeia affinis reworking and ventilation activities on benthic fluxes and mineralization processes during a simulated bloom event. The importance of M. affinis density for benthic solute (O2, ΣNO2− + NO3−, NH4+ and HPO42−) fluxes and sediment reactivity (mobilization of NH4+ and HPO42−) following additions of organic material to the sediment surface was experimentally investigated using sediment-water and closed sediment (jar) incubations. Three different densities of M. affinis were used to resemble a low, medium and high density situation (1300, 2500 and 6400 ind. m− 2, respectively) of a natural amphipod community. The degradation of phytodetritus (Tetraselmis sp., 5 g C m− 2) added to the sediment surface was followed over a period of 20 days. Benthic solute fluxes of O2, ΣNO2− + NO3− and NH4+ were generally progressively stimulated with increasing number of M. affinis, while no such correlation was found for HPO42−. Solute fluxes were initially enhanced 1 to 2 days after the addition of phytodetritius, caused by mineralization of the most labile organic material and a food-stimulated irrigation by the amphipods. There was no effect from the activity of M. affinis on total denitrification (Dtot = Dn + Dw) or denitrification utilizing nitrate from coupled nitrification/denitrification (Dn) for any of the densities examined. Denitrification utilizing overlying water nitrate (Dw) was only about 10% of Dtot. Dw was significantly enhanced for the highest M. affinis density investigated. The reactivity of the sediment decreased progressively with increasing density of M. affinis and with time of the experiment. However, enhanced ammonium production at least 6 days after the organic addition indicated excretion of N-containing organic compounds by M. affinis. In conclusion, large spatial and temporal variations in density of M. affinis may be of significant importance for benthic solute fluxes and overall mineralization of organic material in Baltic Sea sediments. 相似文献
15.
Regan A. McNatt James A. Rice 《Journal of experimental marine biology and ecology》2004,311(1):147-156
As eutrophication of coastal waters increases, water quality issues such as hypoxia have come to the forefront of environmental concerns for many estuarine systems. Chronic hypoxia during the summer has become a common occurrence in numerous estuaries, degrading nursery habitat and increasing the potential for exposure of juvenile fish to low levels of dissolved oxygen (DO).We conducted a laboratory study to investigate how hypoxic conditions and temperature affect growth rates of two juvenile estuary-dependent fish: the Atlantic menhaden (Brevoortia tyrannus) and spot (Leiostomus xanthurus). For a 2-week period, we exposed the fish to one of four constant DO levels (6.0, 4.0, 2.0 or 1.5 mg O2 l−1), at one of two temperatures (25 or 30 °C). A fifth DO treatment, included for spot at 30 °C, allowed DO to fluctuate from 10.0 mg O2 l−1 during the day, to 2.0 mg O2 l−1 at night. This diel fluctuation approximated the natural DO cycle in tidal estuarine creeks. Size measurements were recorded at the beginning, middle and end of experiments.Growth rates were generally unaffected by low DO until concentrations dropped to 1.5 mg O2 l−1, resulting in 31-89% growth reductions. Our results suggest that DO levels must be severely depressed, and in fact, approaching lethal limits, to negatively impact growth of juvenile spot and Atlantic menhaden. 相似文献
16.
Shifts in the relative availability of phosphorus and nitrogen along estuarine salinity gradients 总被引:1,自引:0,他引:1
Phosphorus (P) availability in estuaries may increase with increasing salinity because sulfate from sea salt supports production of sulfide in sediments, which combines with iron (Fe) making it less available to sequester P. Increased P availability with increased salinity may promote the generally observed switch from P limitation of primary production in freshwater ecosystems to nitrogen (N) limitation in coastal marine waters. To investigate this hypothesis, we analyzed pore water from sediment cores collected along the salinity gradients of four Chesapeake Bay estuaries (the Patuxent, Potomac, Choptank, and Bush Rivers) with watersheds differing in land cover and physiography. At salinities of 1–4 in each estuary, abrupt decreases in pore water Fe2+ concentrations coincided with increases in sulfate depletion and PO4 3? concentrations. Peaks in water column PO4 3? concentrations also occur at about the same position along the salinity gradient of each estuary. Increases in pore water PO4 3? concentration with increasing salinity led to distinct shifts in molar NH4 +:PO4 3? ratios from >16 (the Redfield ratio characteristic of phytoplankton N:P) in the freshwater cores to <16 in the cores with salinities >1 to 4, suggesting that release of PO4 3? from Fe where sediments are first deposited in sulfate-rich waters could promote the commonly observed switch from P limitation in freshwater to N limitation in mesohaline waters. Finding this pattern at similar salinities in four estuaries with such different watersheds suggests that it may be a fundamental characteristic of estuaries generally. 相似文献
17.
Nitrate reductase activity (NRA) in different compartments (leaves, inflorescence stalks, flowers and tuberous roots) of Asphodelus aestivus Brot. (Liliaceae) and actual mineral nitrogen (NO3−-N and NH4+-N) in soil surrounding the roots were investigated over one year. Although the highest NRA was found in the leaves, the other plant compartments, such as flowers and tuberous roots, also have nitrate assimilation capacity. High nitrate assimilation capacity under suitable conditions is considered to be a good strategy for development and dominance of this species in Mediterranean environments. There was a seasonal variation in nitrate assimilation in leaves and actual NO3−-N content of soils. Depending on actual nitrate content of soils, nitrate assimilation increased in winter. 相似文献
18.
The rhizostome jellyfishes, Catostylus mosaicus and Phyllorhiza punctata abound in estuaries in New South Wales, Australia. P. punctata contains symbiotic zooxanthellae but C. mosaicus contains few or no zooxanthellae. Our experiment measured the rates at which NH3, PO4 and NOx were taken up or excreted by each species and in two controls: a “water only” control and a “mucus” control. Rates of uptake or excretion were measured as changes in the nutrient concentration of the water in the containers housing the animals over periods of 6 h. Experiments were repeated twice during the day and twice at night, under both ambient and enriched nutrient conditions. Under ambient nutrient conditions, the flux of NH3 in the P. punctata treatment did not differ from the controls but under enriched conditions P. punctata excreted NH3 during the night (49 μg kg−1 WW (wet weight) h−1) and took up NH3 during the day (123 μg kg−1 WW h−1). In contrast, C. mosaicus excreted NH3 at a rate of 1555 μg kg−1 WW h−1 during the day and 1004 μg kg−1 WW h−1 during the night under both enriched and ambient nutrient conditions. P. punctata neither took up nor excreted PO4 but C. mosaicus excreted PO4 at a faster rate during the day than night (173 μg kg−1 WW h−1 cf. 104 μg kg−1 WW h−1). Both C. mosaicus and P. punctata excreted NOx and, although the rate of excretion for P. punctata varied between the two experiments conducted during the day, the rate of excretion was consistently greater than for C. mosaicus (52 and 80 μg kg−1 WW h−1 cf. 26 μg kg−1 WW h−1). Tubs containing P. punctata had a much greater concentration of dissolved oxygen at the end of the experiments conducted during the day (152% saturation) than night (60% saturation) but tubs containing C. mosaicus had a greater dissolved oxygen concentration during the night (47% saturation) than day (39%). Overall, C. mosaicus appears to recycle more inorganic nutrients to estuaries than P. punctata. Calculations of the importance of inorganic nitrogen excreted by this species during times of peak biomass in Lake Illawarra suggest that it can meet about 8% of the phytoplankton primary production requirements of N and that its inorganic N excretion rate is about 11% of measured inorganic ammonia fluxes from sediments in that system. Since the biomass of C. mosaicus often exceeds several thousand tonnes, the contribution of inorganic nutrients by this species is substantial. 相似文献
19.
Rates of chlorophyll synthesis and degradation were analyzed in Synechocystis sp. PCC 6803 wild type and mutants lacking one or both photosystems by labeling cells with (15NH4)2SO4 and Na15NO3. Pigments extracted from cells were separated by HPLC and incorporation of the 15N label into porphyrins was subsequently examined by MALDI-TOF mass spectrometry. The life time (τ) of chlorophyll in wild-type Synechocystis grown at a light intensity of 100 μmol photons m−2 s−1 was determined to be about 300 h, much longer than the cell doubling time of about 14 h. Slow chlorophyll degradation (τ ∼200-400 h) was also observed in Photosystem I-less and in Photosystem II-less Synechocystis mutants, whereas in a mutant lacking both Photosystem I and Photosystem II chlorophyll degradation was accelerated 4-5 fold (τ ∼50 h). Chlorophyllide and pheophorbide were identified as intermediates of chlorophyll degradation in the Photosystem I-less/Photosystem II-less mutant. In comparison with the wild type, the chlorophyll synthesis rate was five-fold slower in the Photosystem I-less strain and about eight-fold slower in the strain lacking both photosystems, resulting in different chlorophyll levels in the various mutants. The results presented in this paper demonstrate the presence of a regulation that adjusts the rate of chlorophyll synthesis according to the needs of chlorophyll-binding polypeptides associated with the photosystems. 相似文献
20.
Bente Aa. Lomstein Lise Bonne Guldberg Anne-Turi Amtoft Neubauer Jesper Hansen Andrew Donnelly Rodney A. Herbert Pierluigi Viaroli Gianmarco Giordani Roberta Azzoni Rutger de Wit Kai Finster 《Aquatic Botany》2006
The degradation of an Ulva lactuca mat (0.2 kg dw m−2) was studied in a controlled flow-through mesocosm for 31 d. Sediment chambers without U. lactuca served as controls. Fluxes of ∑CO2, O2, inorganic nitrogen, and urea were determined during the incubation period in addition to sulfate reduction rates, POC and PON content, enumeration of specific bacterial populations and evaluation of the physiological state of the added U. lactuca thalli. After U. lactuca addition to the chambers, there was an immediate increase in the efflux of ∑CO2 from 11 to 27 mmol-C m−2 d−1 and a concomitant increase in O2 uptake from 11 to 23 mmol m−2 d−1. These effluxes remained elevated throughout the incubation period. In contrast, the NH4+ efflux increased from 0.1 to 1.8 mmol NH4+ m−2 d−1 during the first 3 d of incubation, followed by 6 d with a constant efflux rate, after which time it decreased gradually to 0.3 mmol NH4+ m−2 d−1 by the end of the experiment. In total, NH4+accounted for 83% of the total nitrogen efflux after addition of U. lactuca. During the 31 d incubation period there was a continuous colonization of the thalli by bacteria. Sulfate reducers associated with the thalli accounted for 3% of the carbon oxidation on day 31. The molar C:N ratio in mineralization products (the ratio between the efflux of ∑CO2 and NH4+ + NO2− + NO3−) increased from 15 mol mol−1 at day 11 after U. lactuca addition to >80 mol mol−1 by the end of the incubation. Since the C:N ratio in the mineralization products was much higher than the original thallus material (8.9 mol mol−1) it is probable that a preferential incorporation of NH4+ into the increasing bacterial biomass occurred. The nitrogen for bacterial growth was most likely obtained from degradation of U. lactuca thalli as there was no stimulation of urea-N turnover in the sediment during incubation. The net increase in bacteria cell number in the 18-mm thick thallus layer was estimated to be 7.6 × 109 to 2.4 × 1010 bacterial cells cm−3. In contrast, the bacterial cell number remained constant in the −Ulva incubations. 相似文献