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1.
Annual cycle of gross primary production and respiration in the Viroin River (Belgium) 总被引:1,自引:1,他引:0
Gross primary production, community respiration and reaeration coefficient were determined during an annual cycle on the Viroin
River (South Belgium), based on the daily variations of dissolved oxygen concentration.
Reaeration coefficient remains remarkably constant (0.26 h−1) during the year in spite of discharge variations. The autotrophic community is dominated by ‘Ranunculus fluitans’. Primary production parallels the variations of total solar radiations. It ranges from 0 in winter to 8 g O2 m−2 d−1 in summer. In spring and summer, respiration variations parallel those of primary production (average value: 10 g O2 m−2 d−1); in the dry autumn, decomposition of dying macrophytes considerably enhances the community respiration (15 g O2 m−2 d−1).
A P/R diagram is used to characterize the trophic state of the Viroin. 相似文献
2.
Matteo Campioli Roeland Samson Anders Michelsen Sven Jonasson Robert Baxter Raoul Lemeur 《Plant Ecology》2009,202(1):41-53
Bryophytes and lichens abound in many arctic ecosystems and can contribute substantially to the ecosystem net primary production
(NPP). Because of their growth seasonality and their potential for growth out of the growing season peak, bryophyte and lichen
contribution to NPP may be particularly significant when vascular plants are less active and ecosystems act as a source of
carbon (C). To clarify these dynamics, nonvascular and vascular aboveground NPP was compared for a subarctic heath during
two contrasting periods of the growing season, viz. early-mid summer and late summer-early autumn. Nonvascular NPP was determined
by assessing shoot biomass increment of three moss species (Hylocomium splendens, Pleurozium schreberi and Dicranum elongatum) and by scaling to ecosystem level using average standing crop. For D. elongatum, these estimates were compared with production estimates obtained from measurements of shoot length increase. Vascular NPP
was determined by harvesting shrub and herb apical growth and considering production due to stem secondary growth of shrubs.
Hylocomium splendens and Pleurozium schreberi showed highest biomass growth in late summer, whereas for D. elongatum this occurred in early summer. Maximum relative growth rates were ca. 0.003–0.007 g g−1 d−1. For D. elongatum, production estimates from length growth differed from estimations from biomass growth, likely because of an uncoupling between
length growth and biomass shoot growth. Nonvascular NPP was 0.37 and 0.46 g dry weight m−2 d−1, in early and late summer, respectively, whereas in the same periods vascular NPP was 3.6 and 1.1 g dry weight m−2 d−1. The contribution of nonvascular NPP to total aboveground NPP was therefore minor in early summer but substantial in late
summer, when 25% of the C accumulated by the vegetation was incorporated into nonvascular plant tissue. The expected global
change-induced reduction of nonvascular plant biomass in subarctic heath is likely therefore to enhance C release during the
late part of the growing season. 相似文献
3.
The long-term culture of the coccolithophore Pleurochrysis carterae (Haptophyta) in outdoor raceway ponds 总被引:2,自引:0,他引:2
The calcareous marine haptophyte algae, the coccolithophorids, are of global environmental significance because of the impact of their blooms on the carbon cycle. The coccolithophorid, Pleurochrysis carterae was grown semi-continuously in paddlewheel-driven outdoor raceway ponds over a period of 13 months in Perth, Western Australia. The mean total dry weight productivity of P. carterae was 0.19 g.L−1.d−1 with cell lipid and CaCO3 contents of up to 33% and 10% of dry weight respectively, equivalent to an annual total biomass productivity of about 60 t.ha−1.y−1 and 21.9 t.ha−1.y−1 total lipid and 5.5 t.ha−1.y−1 total calcium carbonate production. Throughout the culture period there was little protozoan contamination or contamination by other algae. The pH of the growth medium increased to pH 11 during the day and was found to be a useful variable for monitoring the state of the culture. A comparison of the growth of P. carterae and Dunaliella salina in the raceway ponds showed no significant differences between these two species with regard to areal total dry weight productivity and lipid content. 相似文献
4.
Fieldwork was carried out at Kerguelen Islands. Two groups of stations in a coastal area, the Morbihan gulf, were surveyed.
At both stations, macroplankton biomass ranged from 2.3 mg dry weight m−3 to 89 mg dry weight m−3 and consisted mostly of Themisto gaudichaudii with values ranging from 1.9 mg dry weight m−3 to 50.6 mg dry weight m−3. Biomass was high for sub-Antarctic waters with marked seasonal and inter-zone differences. Biomass minima were observed
at the end of the winter, from September to November, while maxima were recorded in summer and in early fall at the beginning
of the year between January and April. T. gaudichaudii showed a recruitment of new size classes, mainly from November to January, followed by a rapid growth phase in summer, which
slowed down during the southern winter period. Individuals breed after 1 year. Large individuals, older than 1 year, were
not a significant presence in the gulf of Morbihan. The main pattern of the population dynamics were characterised by an univoltine
life cycle with a very high biomass marked by a strong seasonal signal linked with the hydrological and trophic parameters
of the Gulf. 相似文献
5.
Population of the freshwater amphipod Gammarus fossarum was investigated in a calcareous stream with almost constant temperature (7–8°C) in the Chočské Vrchy Mts (West Carpathians,
Slovakia). Quantitative samples of G. fossarum taken during 2005 showed population densities varying from 100 m−2 in August to 585 m−2 in late November. The population was split into juveniles, mature males, mature females without eggs and females with eggs.
The percentage of juveniles (40–64%) was always the highest of any of the categories. Ovigerous females occurred throughout
the year. The mean sex ratio was 1: 2.4 (male: female), although its values varied considerably with the time of year. Breeding
was continuous, although juvenile recruitment peaked in early spring, summer and early winter. Three discrete cohorts were
distinguished from the size frequency distributions. The life span was 6–7 months and the individuals matured approximately
in the half of life cycle. The mean fecundity was 9.6 embryos per brood. Variation in fecundity was mostly explained by size
of the incubating females. The absolute growth of this species was best described by the Gompertz growth function. Relative
growth rates (% body DM day−1) fluctuated in a nonlinear manner with size and age. The highest values of daily growth (2–4% of dry mass per day) were noted
approximately in the half of life cycle. Annual production, estimated by the size-frequency method, was 1618.9 g dry mass
m−2 and P/B ratio was 5.15. 相似文献
6.
Synchrony, one of the main traits of population life histories, refers to the degree to which individuals complete a certain
stage of the life cycle at the same time. It can be governed by temperature, variations in temperature, photoperiodic cues,
detritus inputs, or discharge regimes. We investigated life cycles and secondary production of five caddisfly species in a
second order stream in the Patagonian Mountains. In addition, we analyzed what environmental variables were implied in the
caddisfly assemblage variation. Mastigoptila sp. (Glossosomatidae) and Eosericostoma aequispina (Helicophidae), Myotrichia murina (Sericostomatidae), Brachysetodes quadrifidus (Leptoceridae), and Neoatopsyche brevispina (Hydrobiosidae) showed univoltine life cycles, with an extended recruitment with no overlapping cohorts and a relatively
well-synchronized imaginal emergence taking place during spring summer seasons. However, Myotrichia murina (Sericostomatidae) displayed a complex life cycle with mixed populations taking 10–12 months to develop, and pupae being
collected almost continuously. The annual secondary production per species varied from 11.06 (E. aequispina) to 310.5 mg m−2 year−1 (M. murina), being overall caddisfly production (0.5 g m−2 year−1) similar to that reported for cold springs in other regions. The highest growth rates (K) were observed during late winter and spring (mostly September) and ranged from 0.70 to 3.70% day−1 in M. longicornuta and N. brevispina, respectively. Redundancy analysis indicated that seasonally dynamic variables, water temperature, discharge, and detritus
biomass were the main predictors of caddisfly assemblage variation; consequently at this cold stream (mean annual 5.9°C),
with a regular availability of food supply, these parameters ruled Trichoptera life histories and secondary production. As
documented for other mountainous temperate areas, synchrony would be a dominant trait on life histories of Trichoptera species
inhabiting Patagonian streams. 相似文献
7.
Patricia Torres-Cañabate Eric A. Davidson Ekaterina Bulygina Roberto García-Ruiz Jose A. Carreira 《Biogeochemistry》2008,91(1):1-11
Evidence for abiotic immobilization of nitrogen (N) in soil is accumulating, but remains controversial. Identifying the fate
of N from atmospheric deposition is important for understanding the N cycle of forest ecosystems. We studied soils of two
Abies pinsapo fir forests under Mediterranean climate seasonality in southern Spain—one with low N availability and the other with symptoms
of N saturation. We hypothesized that biotic and abiotic immobilization of nitrate (NO3
−) would be lower in soils under these forests compared to more mesic temperate forests, and that the N saturated stand would
have the lowest rates of NO3
− immobilization. Live and autoclaved soils were incubated with added 15NO3
− (10 μg N g−1 dry soil; 99% enriched) for 24 h, and the label was recovered as total dissolved-N, NO3
−, ammonium (NH4
+), or dissolved organic-N (DON). To evaluate concerns about possible iron interference in analysis of NO3
− concentrations, both flow injection analysis (FIA) and ion chromatography (IC) were applied to water extracts, soluble iron
was measured in both water and salt extracts, and standard additions of NO3
− to salt extracts were analyzed. Good agreement between FIA and IC analysis, low concentrations of soluble Fe, and 100% (±3%)
recovery of NO3
− standard additions all pointed to absence of an interference problem for NO3
− quantification. On average, 85% of the added 15NO3
− label was recovered as 15NO3
−, which supports our hypothesis that rates of immobilization were generally low in these soils. A small amount (mean = 0.06 μg N g−1 dry soil) was recovered as 15NH4
+ in live soils and none in sterilized soils. Mean recovery as DO15N ranged from 0.6 to 1.5 μg N g−1 dry soil, with no statistically significant effect of sterilization or soil type, indicating that this was an abiotic process
that occurred at similar rates in both soils. These results demonstrate a detectable, but modest rate of abiotic immobilization
of NO3
− to DON, supporting our first hypothesis. These mineral soils may not have adequate carbon availability to support the regeneration
of reducing microsites needed for high rates of NO3
− reduction. Our second hypothesis regarding lower expected abiotic immobilization in soils from the N-saturated site was not
supported. The rates of N deposition in this region may not be high enough to have swamped the capacity for soil NO3
− immobilization, even in the stand showing some symptoms of N saturation. A growing body of evidence suggests that soil abiotic
NO3
− immobilization is common, but that rates are influenced by a combination of factors, including the presence of plentiful
available carbon, reduced minerals in anaerobic microsites and adequate NO3
− supply. 相似文献
8.
Francis Q. Brearley Julie D. Scholes Malcolm C. Press Götz Palfner 《Plant Ecology》2007,192(2):237-249
Phosphorus concentrations in many south-east Asian tropical rain forest soils are very low. To determine the growth responses
of seedlings of a light-demanding (Shorea leprosula) and a more shade-tolerant (Hopea nervosa) dipterocarp species to increasing P, we carried out a nursery fertilisation experiment. Responses of symbiotic ectomycorrhizal
(EcM) fungi to the treatments were also determined. Seedlings were grown under high light (13 mol m−2 d−1) or moderate light (4 mol m−2 d−1) in shade-chambers and were fertilised with a solution containing 0, 1, 10 or 100 mg L−1 P. The growth of Hopea and Shorea showed different responses to the light and P fertilisation treatments with Hopea having greater growth under moderate light conditions and Shorea having greater growth under high light conditions. Shorea responded to P fertilisation by increasing its foliar P concentrations and growth rates, whereas Hopea did not take up additional P and did not improve its growth rates. There was no effect of either light or P fertilisation
on total EcM colonisation or EcM diversity, but around half of the EcM morphotypes observed were affected by one of these
two abiotic perturbations, most notably for Riessiella sp. which increased with P fertilisation suggesting it may not be a mutualistic fungus. These results show how niche partitioning
in both dipterocarp seedlings and EcM fungi can be divided along contrasting axes. 相似文献
9.
In this study, the effects of citrate addition on d-ribose production were investigated in batch culture of a transketolase-deficient strain, Bacillus subtilis EC2, in shake flasks and bioreactors. Batch cultures in shake flasks and a 5-l reactor indicated that supplementation with
0.2–0.5 g l−1 of citrate enhanced d-ribose production. When B. subtilis EC2 was cultivated in a 15-l reactor in a complex medium, the d-ribose concentration was 70.9 g l−1 with a ribose yield of 0.497 mol mol−1. When this strain was grown in the same medium supplemented with 0.3 g l−1 of citrate, 83.4 g l−1 of d-ribose were obtained, and the ribose yield was increased to 0.587 mol mol−1. Addition of citrate reduced the activities of pyruvate kinase and phosphofructokinase, while it increased those of glucose-6-phosphate
dehydrogenase and 6-phosphogluconate dehydrogenase. Metabolic flux distribution in the stationary phase indicated that citrate
addition resulted in increased fluxes in the pentose phosphate pathway and TCA cycle, and decreased fluxes in the glycolysis
and acetate pathways. 相似文献
10.
Alleviation of Ultraviolet-B Radiation-Induced Growth Inhibition of Green Gram by Triadimefon 总被引:1,自引:0,他引:1
Supplementary UV-B (12.2 kJ m−2 d−1 UV-BBE) provided to Vigna radiata for 2 h d−1 suppressed the length of root, shoot and whole plants, number of leaves, total leaf area, leaf area index, specific leaf
mass, fresh and dry mass of leaves and shoot, relative growth rate and net productivity. In unstressed green gram plants (10
kJ m−2 d−1 UV-BBE), triadimefon (TRIAD) (20 mg dm−3) enhanced growth in all parameters over control. The growth promoting effect of TRIAD enabled the UV-B impacted plants to
overcome the growth inhibitions to varying degrees indicating its protective potential against UV-B stress.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
The spring mesozooplankton community at South Georgia: a comparison of shelf and oceanic sites 总被引:3,自引:3,他引:0
Mesozooplankton (predominantly 200–2000 μm) were sampled at a shelf and an oceanic station close to South Georgia, South
Atlantic, during austral spring (October/November) 1997. Onshelf zooplankton biomass was extremely high at 10–16 g dry mass
m−2 (0–150 m), 70% comprising the small neritic clausocalaniid copepod Drepanopus forcipatus. Large calanoid species, principally Calanoides acutus and Rhincalanus gigas, contributed only 8–10%. At the oceanic station, biomass in the sampled water column (0–1000 m) was ∼6.5 g dry mass m−2 and 4–6 g dry mass m−2 in the top 200 m. Here, large calanoids composed 40–50% of the standing stock. Antarctic krill (Euphausia superba) occurred in low abundances at both stations. Vertical profiles obtained with a Longhurst Hardy Plankton Recorder indicated
that populations of C. acutus and R. gigas, which overwinter at depth, had completed their spring ascent and were resident in surface waters. Dry mass, carbon and lipid
values were lower than found in summer but were consistent with overwintered populations. Phytoplankton concentrations were
considerably higher at the oceanic station (2–3 mg chlorophyll a m−3) and increased over the time on station. In response to this, egg production of both large calanoid species and growth rates
of R. gigas approached those measured in summer. Onshelf phytoplankton concentrations were lower (<1 mg m−3), and low egg production rates suggested food limitation. Here phytoplankton rations equivalent to 6% zooplankton body C
would have been sufficient to clear primary production whereas at the oceanic station daily carbon fixation was broadly equivalent
to zooplankton carbon biomass.
Accepted: 25 April 1999 相似文献
12.
Methanogenesis in Arizona,USA dryland streams 总被引:1,自引:0,他引:1
Jeremy B. Jones Jr. Robert M. Holmes Stuart G. Fisher Nancy B. Grimm Dena M. Greene 《Biogeochemistry》1995,31(3):155-173
Methanogenesis was studied in five streams of central and southern Arizona by examining the distribution of methane in interstitial
water and evasion of methane in three subsystems (hyporheic, parafluvial and bank sediments). In Sycamore Creek, the primary
study site (studied during summer and early autumn), methane content of interstitial water exhibited a distinct spatial pattern.
In hyporheic (sediments beneath the wetted channel) and parfluvial zones (active channel sediments lateral to the wetted channel),
which were well oxygenated due to high hydrologic exchange with the surface stream and had little particulate organic matter
(POM), interstitial methane concentration averaged only 0.03 mgCH4-C/L. Bank sediments (interface between the active channel and riparian zone), in contrast, which were typically vegetated,
had high POM, low hydrologic exchange and concomitantly low dissolved oxygen levels, had interstitial concentration averaging
1.5 mgCH4-C/L. Methane emission from Sycamore Creek, similar to methane concentration, averaged only 3.7 mgCH4-C·m−2·d−1 from hyporheic and parafluvial zones as opposed to 170 mgCH4-C·m−2·d−1 from anoxic bank sediments. Methane in four additional streams sampled (one sampling date during late winter) was low and
exhibited little spatial variation most likely due to cooler stream temperatures. Interstitial methane in parafluvial and
bank sediments of all four streams ranged from only 0.005 to 0.1 mgCH4-C/L. Similarly methane evasion was also low from these streams varying from 0 to 5.7 mgCH4-C·m−2·d−1. The effects of organic matter and temperature on methanogenesis were further examined by experimentally manipulating POM
and temperature in stoppered flasks filled with hyporheic sediments and stream water. Methane production significantly increased
with all independent variables. Methane production is greatest in bank sediments that are relatively isolated hydrologically
and lowest in hyporheic and parafluvial sediments that are interactive with the surface stream. 相似文献
13.
Pakkasmaa S Penttinen OP Piironen J 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2006,176(5):387-391
The metabolic rate (specific heat output) of individual eyed-stage eggs of Arctic charr Salvelinus alpinus (Linnaeus, 1758) originating from different families was measured with direct microcalorimetry. Metabolic rates varied between 2.3–7.9 μW ind−1 and 0.06–0.22 μW mg−1. Absolute heat output was unrelated to egg size, but size-scaled or specific heat output was negatively correlated with egg size, measured as diameter, dry mass or fresh mass. Metabolic rates varied significantly between families, suggesting that genetic and/or maternal effects affect embryonic metabolism in Arctic charr. Heat output increased almost linearly from 3.4 to 16.7 μW ind−1 (0.09–0.67 μW mg−1) during the embryonic development. Although the metabolic rate varied between the families and egg metabolic rate increased during development, there was an unexpected disconnect between metabolic rate and hatching time. 相似文献
14.
Two variants of open photobioreactors were operated at surface-to-volume ratios up to 170 m−1. The mean values for July and September obtained for photobioreactor PB-1 of 224 m2 culture area (length 28 m, inclination 1.7%, thickness of algal culture layer 6 mm), operated in Třeboň (49∘N), Czech Republic, were: net areal productivity, P
net = 23.5 and 11.1 g dry weight (DW) m−2 d−1; net photosynthetic efficiency (based on PAR – Photosynthetic Active Radiation), η = 6.48 and 5.98%. For photobioreactor PB-2 of 100 m2 culture area (length 100 m, inclination 1.6%, thickness of algal culture layer 8 mm) operated in Southern Greece (Kalamata, 37∘N) the mean values for July and October were: P
net = 32.2 and 18.1 g DW m−2 d−1, η = 5.42 and 6.07%. The growth rate of the alga was practically linear during the fed-batch cultivation regime up to high biomass densities of about 40 g DW L−1, corresponding to an areal density of 240 g DW m−2 in PB-1 and 320 g DW m−2 in PB-2. Night biomass loss (% of the daylight productivity, P
L) caused by respiration of algal cells were: 9–14% in PB-1; 6.6–10.8% in PB-2. About 70% of supplied CO2 was utilized by the algae for photosynthesis. The concentration of dissolved oxygen (DO) increased from about 12 mg L−1 at the beginning to about 35 mg L−1 at the end of the 100 m long path of suspension flow in PB-2 at noon on clear summer days. Dissipation of hydraulic energy and some parameters of turbulence in algal suspension on culture area were estimated quantitatively. 相似文献
15.
J. G. Wakibia J. J. Bolton D. W. Keats L. M. Raitt 《Journal of applied phycology》2006,18(3-5):565-573
As a possible means of improving the livelihoods of local villagers, off-bottom rope cultivation of commercial eucheumoids was investigated on the southern Kenyan coast at three sites, representative of the variety of environments. The morphotypes used were brown Eucheuma denticulatum and green and brown Kappaphycus alvarezii. The study was carried out over a 15 month period from August 2001 until October 2002. Relative growth rates were highest at a sandy flat in a mangrove system (Gazi; 5.6% d−1), and lowest in an intertidal reef flat (Kibuyuni; 3.2% d−1) with a lagoon being intermediate (Mkwiro; 4.8% d−1). The brown E. denticulatum had the highest growth rate of 4.7% d−1 compared to the green and brown K. alvarezii which were 4.3% d−1 and 4.2% d−1, respectively. Growth was more variable at Kibuyuni and Mkwiro. The growth was higher during the southeast monsoon (4.7% d−1) than during the northeast monsoon (4.0% d−1). This is part of a larger study and the effects of water motion, salinity, temperature, thallus nitrogen, and ‘ice-ice’ syndrome on growth of morphotypes is discussed. The water motion was observed to increase thallus nitrogen and hence the growth of eucheumoids. The ‘ice-ice’ condition affected both brown E. denticulatum and brown K. alvarezii but not green K. alvarezii. The results suggest that commercial cultivation of eucheumoids in Kenya will be feasible. 相似文献
16.
Biosynthesis of six saponins (ginsenosides) in suspension culture of P. quinquefolium Z5 was investigated. Ginsenoside content in biomass reached the highest level, nearly 30 mg g−1 d.w., between 25 and 30 days of the culture. Saponins were synthesized simultaneously with cell growth but their synthesis
rate was not proportional to the growth rate. During the phase of rapid biomass multiplication, after which biomass reached
90% of its maximum yield, only half examined ginsenosides was produced. The second half of the final saponins yield was produced
during the slow growth phase, in which only 10% of biomass was grown. During the intensive growth phase the productivity of
six saponins examined per biomass (dry weight) unit was 3.4 μg mg−1 d.w. day−1, however, this parameter calculated for slow growth phase reached nearly 30 μg mg−1 d.w. day−1. There were differences in increase of the contents of six saponins determined in biomass, and it was the highest for saponins
Re (20(S)-protopanaxatriol-6-[O-α-l-rhamnopyranosyl(1 → 2)-β-d-glucopyranoside]-20-O-β-d-glucopyranoside) and Rg1 (20(S)-protopanaxatriol-6,20-di-O-β-d-glucoside). 相似文献
17.
Senka S. Vidović Ibrahim O. Mujić Zoran P. Zeković Žika D. Lepojević Vesna T. Tumbas Aida I. Mujić 《Food biophysics》2010,5(1):49-58
Considering the growing interest for mushrooms and the demand search of natural antioxidants sources, the aim of this study
was to investigate the antioxidant properties of two edible widely used Boletus species, Boletus edulis, and Boletus auranticus, collected from Istra region in Croatia in late summer 2007. To evaluate the antioxidant properties and content of antioxidant
compounds, scavenging capacity on DPPH˙, OH˙, and O2˙− radicals, reducing power and capacity to inhibit lipid peroxidation has been investigated. It is determined that content
of total phenols (41.82 ± 0.08 mg gallic acid equivalent per gram of dry extract) was higher for B. edulis. Using high performance liquid chromatography/diode array detector analysis, the main antioxidant compound, variegatic acid,
has been detected and quantified. 1,1-Diphenyl-2-picryl-hydrazyl-hydrate assay was used as a preliminary free radical–scavenging
evaluation. By this assay, it has been found that B. edulis dry mushroom extract exhibits 50% of inhibition value at the extract concentration of 0.016 ± 0.0003 mg/ml. The extracts
were capable of reducing iron(III) and, thus, are capable of donating electrons. Using electron paramagnetic resonance spin-trapping
and spin-probing techniques, activity against relevant reactive species, ˙OH and O2˙− radical, was analyzed for both mushroom extracts. Both investigated extracts are determined as good inhibitors for ˙OH radical
reduction, and both exhibited significant capacity for scavenging O2˙− radical and for that could help to prevent or meliorate oxidative damage. Only B. edulis extract prevents lipid peroxidation. Investigated mushroom extracts could represent easily accessible natural antioxidant
resource. 相似文献
18.
Dalila Serpa Manuela Falcão Pedro Duarte Luís Cancela da Fonseca Carlos Vale 《Biogeochemistry》2007,82(3):291-304
During an annual cycle, overlying water and sediment cores were collected simultaneously at three sites (Tavira, Culatra and
Ramalhete) of Ria Formosa’s intertidal muddy and subtidal sandy sediments to determine ammonium, nitrates plus nitrites and
phosphate. Organic carbon, nitrogen and phosphorus were also determined in superficial sediments. Ammonium and phosphate dissolved
in porewater were positively correlated with temperature (P < 0.01) in muddy and sandy sediments, while the nitrogen-oxidized forms had a negative correlation (P < 0.02) in muddy sediments probably because mineralization and nitrification/denitrification processes vary seasonally. Porewater
ammonium profiles evidenced a peak in the top-most muddy sediment (380 μM) suggesting higher mineralization rate when oxygen
is more available, while maximum phosphate concentration (113 μM) occurred in the sub-oxic layer probably due to phosphorus
desorption under reduced conditions. In organically poor subtidal sandy sediments, nutrient porewater concentrations were
always lower than in intertidal muddy sediments, ranging annually from 20 μM to 100 μM for ammonium and from 0.05 μM to 16 μM
for phosphate. Nutrient diffusive fluxes predicted by a mathematical model were higher during summer, in both muddy (104 nmol cm−2 d−1––NH4+; 8 nmol cm−2 d−1––HPO4−2) and sandy sediments (26 nmol cm−2 d−1––NH4+; 1 nmol cm−2 d−1––HPO4−2), while during lower temperature periods these fluxes were 3–4 times lower. Based on simulated nutrient effluxes, the estimated
annual amount of ammonium and phosphate exported from intertidal areas was three times higher than that released from subtidal
areas (22 ton year−1––NH4+; 2 ton year−1––HPO4−2), emphasizing the importance of tidal flats to maintain the high productivity of the lagoon. Global warming scenarios simulated
with the model, revealed that an increase in lagoon water temperature only produces significant variations (P < 0.05) for NH4+ in porewater and consequent diffusive fluxes, what will probably affect the system productivity due to a N/P ratio unbalance. 相似文献
19.
Exposed rocks with no visible macro-fauna are abundant in all coral reefs. Depletion of phytoplankton cells and pigments by the minute crypto fauna inhabiting the outer few centimeters of such rocks was experimentally studied over an annual cycle in the Gulf of Aqaba, Red Sea. Different substrata were introduced into small (3.6 L), well mixed, tanks that were fed by running seawater pumped directly from the reef at a rate of 11±1 L h−1. A steady-state reduction in phytoplankton abundance and chlorophyll a concentration of 38±26% (mean ± 1 SD) was found for untreated rocks but not for sand, gravel, or killed controls. Average areal clearance rate by untreated rocks was 17.3±8.0 ml cm−2 h−1. Conservative extrapolation of this rate to the whole reef community suggests that the fauna inhabiting exposed rocks clears 2.1±0.9 m3 m−2 d−1 at Eilat. Phytoplankton removal by untreated rocks varied from 1.5 ng chlorophyll a cm−2 h−1 during the oligotrophic summer conditions to 6 ng chlorophyll a cm−2 h−1 during the spring bloom. These values correspond to a potential nitrogen gain of 1.3 and 5.2 mmol N m−2 day−1, respectively. Cryptic reef-rock fauna can have a key role in the biogeochemical functioning of coral reef communities. 相似文献
20.
Naoki Hijii 《Ecological Research》1987,2(2):159-173
Seasonal changes in abundance and distribution pattern of soil micro-arthropods were studied in connection with a few environmental
factors in a Japanese cedar (Cryptomeria japonica
D. Don) plantation. The soil arthropods were sampled from three different depths at intervals of two months for two years. Of the
collected animals (total 51000–155000 m−2), Collembola (20000–76000 m−2), oribatid mites (19000–55000 m−2) and carnivorous mites (6200–21000 m−2) were the numerically dominant animal groups. Low seasonal variations in abundance indicated their seasonal stability in
population levels. The trends in seasonal fluctuation were similar among these groups and between the two years, showing bimodal
pattern with little peaks in early summer and winter. The pattern of seasonal fluctuation in abundance of carnivorous mites
(P
d) was significantly synchronized with that in the total abundance of Collembola and oribatid mites (P
τ). Thus, the number-ratios (P
d/P
τ) were fairly constant, ranging from 0.10 to 0.25. Seasonal changes in vertical distribution of the three animal groups showed
a similar pattern for both years. The downward migrations were shown to be more affected by low temperatures in winter accompanied
by snow coverage rather than by the desiccation of the surface soil in summer. All the three groups demonstrated as a whole
slightly aggregated patterns of horizontal distribution throughout the two years. Temporal increases in the patchiness indices
were observed from summer to autumn when the moisture content of the surface soil was low. 相似文献