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1.
Effects of the herbicide linuron on photosynthesis of the freshwater macrophytes Elodea nuttallii (Planchon) St. John, Myriophyllum
spicatum L., Potamogeton crispus L., Ranunculus circinatus Sibth., Ceratophyllum demersum L. and Chara globularis (Thuill.),
and of the alga Scenedesmus acutus Meyen, were assessed by measuring the efficiency of photosystem II electron flow using
chlorophyll fluorescence.
In a series of single-species laboratory tests several plant species were exposed to linuron at concentrations ranging from
0 to 1000 μg l−1. It was found that the primary effect of linuron, inhibition of photosystem II electron flow, occurred with
a half-lifetime of about 0.1 to 1.9 h after addition of linuron to the growth medium. The direct effect of the herbicide on
photosynthesis appeared to be reversible. Complete recovery from the inhibition occurred with a half-lifetime of 0.5 to 1.8 h
after transfer of linuron treated plants to linuron free medium. The EC50,24h of the inhibition of photosystem II electron
transport by linuron was about 9–13 μg l−1 for most of the macrophytes tested. For S. acutus the EC50,72h for inhibition of
photosystem II electron flow was about 17 μg l−1 for the free suspension, and 22 μg l−1 for cells encapsulated in alginate
beads.
In a long-term indoor microcosm experiment, the photosystem II electron flow of the macrophytes E. nuttallii, C. demersum
and the alga Spirogyra sp. was determined during 4 weeks of chronic exposure to linuron. The EC50,4weeks for the long-term
exposure was 8.3, 8.7 and 25.1 μg l−1 for E. nuttallii, C. demersum and Spirogyra, respectively. These results are very similar
to those calculated for the acute effects. The relative biomass increase of E. nuttallii in the microcosms was determined
during 3 weeks of chronic exposure and was related to the efficiency of photosystem II electron transport as assessed in the
different treatments.
It is concluded that effects of the photosynthesis inhibiting herbicide on aquatic macrophytes, algae and algae encapsulated
in alginate beads can be conveniently evaluated by measuring photosystem II electron transport by means of chlorophyll fluorescence.
This method can be used as a rapid and non-destructive technique in aquatic ecological research.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
Kwang-Hyeon Chang Masaki Sakamoto Jin-Yong Ha Yuichi Miyabara Shin-ichi Nakano Hideyuki Doi Takayuki Hanazato 《Limnology》2011,12(1):11-16
The methylthiotriazine herbicide, simetryn, is commonly used in Japan, and its concentration in surface water is often high
enough to affect natural phytoplankton. To estimate how the plankton community in eutrophic systems respond to short-term
exposure of realistic concentrations of simetryn, we collected plankton from a eutrophic lake and exposed them to low (20 μg l−1) and high (100 μg l−1) concentrations of simetryn for 12 days in microcosm tanks (50 l). High concentrations significantly lowered total phytoplankton
biomass, particularly green algal density. Consequently, the species composition was severely modified by simetryn application.
However, there was no apparent impact of simetryn on microbial food-web components, bacteria, heterotrophic nanoflagellates
(HNF), and ciliates. Despite the decreased abundance of algal food, the zooplankton community showed subtle changes with simetryn
application. The results indicate that the direct impact of simetryn on planktonic organisms other than phytoplankton, particularly
on microbial food-web components, is weak. The indirect impact of simetryn on zooplankton through the change of food quality
and quantity was also small. It has been suggested that the persistence of microorganisms, alternative food for zooplankton,
probably dilutes the indirect impact of simetryn on zooplankton by compensating for the loss of food phytoplankton. Consequently,
the plankton community in eutrophicated systems is resistant to the herbicide at a feasible concentration for a short period
of time. 相似文献
3.
Three post-emergence herbicides (2,4-D, picloram and glyphosate) were applied to samples of an Alberta agricultural soil at
concentrations of 0, 2, 20, and 200 μg g−1. The effects of these chemicals on certain microbial variables was monitored over 27 days. All herbicides caused enhancement
of basal respiration but only for 9 days following application, and only for concentrations of 200 μg g−1. Substrate-induced respiration was temporarily depressed by 200 μg g−1 picloram and 2,4-D, and briefly enhanced by 200 μg g−1 glyphosate. It is concluded that because changes in microbial variables only occurred at herbicide concentrations of much
higher than that which occurs following field application, the side-effects of these chemicals is probably of little ecological
significance. 相似文献
4.
Elizabeth M. Hartgers G.H. Aalderink Paul J. Van den Brink Ronald Gylstra J. Wilfred F. Wiegman Theo C.M. Brock 《Aquatic Ecology》1998,32(2):135-152
Twelve indoor, plankton-dominated, freshwater microcosms (600 l) were used to study the effect of a mixture of herbicides
on structural and functional aspects of these ecosystems. The EC50, 72 h values of the most susceptible standard test alga
Selenastrum capricornutum (EC50, atrazine=54 μg l−1, EC50, diuron=15 μg l−1, EC50, metolachlor=56 μg l−1) were used as a starting
point for the dosage applied in the microcosms (dosages: 0, 0.01, 0.03, 0.1, 0.3, 1× EC50). The microcosms were exposed to
chronic levels for 28 days and subsequently monitored for 4 more weeks.
The following effects were observed: (1) direct effects became apparent from an initial drop in photosynthesis efficiency,
pH and oxygen concentration and a decrease in the abundance of several phytoplankton taxa at the 0.3 × EC50 treatment level
and higher. (2) Fourteen days post application an increase in the abundance of several phytoplankton taxa (Chlamydomonas sp.
and Stephanodiscus/Cyclotella) was observed; oxygen concentrations recovered while alkalinity, conductivity and total inorganic
nitrogen were elevated. (3) Effects on fauna were minor. Daphnia galeata showed a decreasing trend and the cyclopoid copepods
an increasing trend at the end of the experiment.
Multivariate statistical analyses demonstrated no effects of any treatment level on the zooplankton community. Effects were
reported for the phytoplankton community at dose levels of 0.3 × EC50 and higher. On species level the most sensitive taxon
was Chlorophyceae coccales. For this taxon a NOEC at the dose level of 0.01 × EC50 was calculated. This effect however was
relatively small in magnitude and merely based on an increase in numbers in the control and lowest treated microcosms rather
than a decrease in numbers in all other treatments. The standards based on algal toxicity data, as adopted by the Uniform
Principles, consist of a safety factors of 0.1 to be multiplied with the EC50. The NOEC of coccales was lower than 0.1 × EC50.
All other observed variables in this aquatic ecosystem were sufficiently protected against the mixture of herbicides by the
safety factor as proposed in the Uniform Principles.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
The side effects of glyphosate on the soil microflora were monitored by applying a range of glyphosate concentrations (0,
2, 20, and 200 μg g−1 herbicide) to incubated soil samples, and following changes in various microbial groups over 27 days. Bacterial propagule
numbers were temporarily enhanced by 20 μg g−1 and 200 μg g−1 glyphosate, while actinomycete and fungal propagule numbers were unaffected by glyphosate. The frequency of three fungal
species on organic particles in soil was temporarily enhanced by 200 μg g−1 glyphosate, while one was inhibited. One species was temporily enhanced on mineral particles. However, many of these fungi
were inhibited by 200 μg g−1 glyphosate in pure culture. There was little agreement between species responses to glyphosate in incubated soil samples
and in pure culture. 相似文献
6.
U. H. Brockmann 《Aquatic Ecology》1994,28(3-4):371-381
In the low salinity region of the Elbe estuary in March–April 1992 the turbidity zone was characterized by high loads of suspended
matter, 7% of which was organic material (750 μM C) at the surface. Particulate nitrogen, phosphorus and carbohydrates concentrations
reached 55 μM N, 10 μM P and more than 15 μM glc. eq., corresponding to 13% of total C, at the surface and increasing threefold
near the bottom.
In spite of the peaking of particulate organic material levels in the maximum turbidity zone, there were only consistent qualitative
changes in total particulate C, N, P, and carbohydrates along the Elbe estuary. Downstream, both the percentage of particulate
organic material and the turbidity: organic material ratio decreased, indicating decomposition in the upper estuary and dilution
with inorganic suspended matter from the lower estuary.
Diatoms, the dominant phytoplankton group, decreased from the upper reaches towards the turbidity zone by 0.3 (surface) and
1.5 mg C l−1 (bottom). This corresponded to 12 and 60% of the decrease in total particulate carbon. Estimated local input of organic carbon
by primary production (21 μg Cl−1d−1) was almost compensated by calculated minimum grazing (14 μg C l−1d−1). Considering net primary production and grazing, the dissimilation by zooplankton (5 μg C l−1d−1) and heterotrophic bacterial decomposition (48 μg C l−1d−1), when summed over the estimated flushing time (12 days) represented a loss of suspended organic matter of 0.6 mg Cl−1. Since this was only 20% of the observed decrease in particulate carbon, significant dilution processes must be assumed.
Dissolved organic nitrogen decreased from 35 to 10 μM N and dissolvd organic phosphorus from 0.6 to 0.1 μM P towards the sea,
mainly due to dilution. The distribution of phosphate, with highest loads in the turbidity maximum of 2.4 μM, suggested an
interaction with the accumulated load of particulate material. 相似文献
7.
Castor bean (Ricinus communis L.) plants were grown for 5–7 weeks in a controlled environment at 350 μl l−1 or 700 μl l−1 CO2. Carbon assimilation, assimilate deposition, dark respiration and assimilate mobilization were measured in leaves 2, 3 and
4 (counted from the base of the plant), and a balance sheet of carbon input and export was elaborated for both CO2 concentrations. Carbon dioxide assimilation was nearly constant over the illumination period, with only a slight depression
occurring at the end of the day in mature source leaves, not in young source leaves. Assimilation was ca. 40% higher at 700 μl l−1 than at 350 μl l−1 CO2. The source leaves increased steadily in weight per unit area during the first 3 weeks, more at 700 μl l−1 than at 350 μl l−1 CO2. On top of an irreversible weight increase, there was a large gain in dry weight during the day, which was reversed during
the night. This reversible weight gain was constant over the life time of the leaf and ca. 80% higher at 700 μl l−1 than at 350 μl l−1. Most of it was due to carbohydrates. The carbon content (as a percentage) was not altered by the CO2 treatment. Respiration was 25% higher in high-CO2 plants when based on leaf area, but the same when based on dry weight. The rate of carbon export via the phloem was the same
during the daytime in plants grown at 350 μl l−1 and 700 μl l−1 CO2. During the night the low-CO2 plants had only 50% of the daytime export rate, in contrast to the high-CO2 plants which maintained the high export rate. It was concluded that the phloem loading system is saturated during the daytime
in both CO2 regimes, whereas during the night the assimilate supply is reduced in plants in the normal CO2 concentration. Two-thirds of the carbon exported from the leaves was permanently incorporated as plant dry matter in the
residual plant parts. This “assimilation efficiency” was the same for both CO2 regimes. It is speculated that under 350 μl l−1 CO2 the growing Ricinus plant operates at sink limitation during the day and at source limitation during the night.
Received: 2 February 1999 / Accepted: 19 April 1999 相似文献
8.
Yasuhiro Satoh Toshiya Katano Takeshi Satoh Osamu Mitamura Kaori Anbutsu Shin-ichi Nakano Hiroyuki Ueno Masaki Kihira Valentin Drucker Yuji Tanaka Tetsuro Mimura Yasunori Watanabe Masahito Sugiyama 《Limnology》2006,7(3):225-229
Nutrient limitation of the primary production of phytoplankton at some stations in southern and central Lake Baikal was studied
by nutrient enrichment experiments in August 2002. Chlorophyll (Chl.) a concentrations ranged from 0.7 to 5.8μgl−1. Inorganic nutrient concentrations were low: soluble reactive phosphorus ranged from 0.05 to 0.20μmoll−1, ammonia from 0.21 to 0.41μmoll−1, and nitrite plus nitrate from 0.33 to 0.37μmoll−1. In the five enrichment experiments, phosphate spikes and phosphate plus nitrate spikes always stimulated primary production.
Nitrate spikes also stimulated primary production in four of the experiments. Significant differences were detected between
the controls and phosphate spikes and between the controls and phosphate plus nitrate spikes. Thus, the first limiting nutrient
is thought to be phosphorus, but once phosphorus is supplied to the surface water, the limiting nutrient will quickly shift
from phosphorus to nitrogen. 相似文献
9.
Phosphorus (P) to chlorophyll ratios and zooplankton–phytoplankton (Z:P) biomass ratios were assessed in 400 temperate lakes
over a gradient of phosphorus (P) and with different fish communities. Most of the lakes in this survey were oligotrophic,
with a median total P of 7.3 μg P L−1. Thus, the survey provided information on food web effects during the early phase of eutrophication. There was no tendency
toward a reduced yield of autotrophs per unit of P over the gradient covered in this survey. The zooplankton yield per unit
of P or chlorophyll a decreased slightly with increased nutrient concentrations, and Z:P biomass ratios decreased with fish community classes,
reflecting increased fish predation pressure. However, the variability in biomass ratios within a given range of P and fish
class was some 100 times higher than the difference over the gradients. This finding suggests that lake-specific properties,
community composition, and food quality are by far the most important determinants of biomass ratios and probably also trophic
efficiency in lakes; it further suggests that these factors are superimposed on the general effect of eutrophication, at least
up to 30 μg P L−1. 相似文献
10.
Experimental study of the impacts of silver carp on plankton communities of eutrophic Villerest reservoir (France) 总被引:5,自引:0,他引:5
We examined the impact of five silver carp biomass levels (0, 8, 16, 20, and 32 g m−3) on plankton communities and water quality of Villerest eutrophic reservoir (France). We realized the experiments using outdoor
mesocosms. The presence of silver carp led to changes in zooplankton and phytoplankton assemblages. High fish biomass strongly
reduced cladoceran abundance (through predation). Silver carp inefficiently grazed down particles < 20 μm. More importantly,
however, the suppression of herbivorous cladocerans resulted in the increase of small size algae which were relieved from
grazing and benefit from high nutrient concentrations.
In contrast, in mesocosms without fish, the dominance of cladocerans (mainly Daphnia) controlled small size algae and probably
also larger size algae (colonial chlorophytes, cyanobacteria). Thus, the Secchi disc transparency increased markedly. Through
cascade effects, the modification of grazers communities led to changes in the utilization patterns of the added nutrients
by phytoplankton communities. In high fish biomass treatments, nutrients were more efficiently accumulated into particulate
fractions compared with no-fish and low-fish biomass treatments that were characterized by higher dissolved nutrients concentrations.
Zooplankton was an essential source of food for silver carp. The productivity of zooplankton sustained a moderate silver carp
biomass (up to 16 g m−3). In the presence of the highest fish biomass, the productivity of zooplankton was not large enough and silver carps fed
on additional phytoplankton. Although mesocosms with high fish biomass were characterized by a slight cyanobacteria development
compared with other fish mesocosms, silver carp was not effective in reducing cyanobacteria dominance.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
Long-term exposure of native vegetation to elevated atmospheric CO2 concentrations is expected to increase C inputs to the soil and, in ecosystems with seasonally dry periods, to increase soil
moisture. We tested the hypothesis that these indirect effects of elevated CO2 (600 μl l−1 vs 350 μl l−1) would improve conditions for microbial activity and stimulate emissions of nitrous oxide (N2O), a very potent and long-lived greenhouse gas. After two growing seasons, the mean N2O efflux from monoliths of calcareous grassland maintained at elevated CO2 was twice as high as that measured from monoliths maintained at current ambient CO2 (70 ± 9 vs 37 ± 4 μg N2O m−2 h−1 in October, 27 ± 5 vs 13 ± 3 μg N2O m−2 h−1 in November after aboveground harvest). The higher N2O emission rates at elevated CO2 were associated with increases in soil moisture, soil heterotrophic respiration, and plant biomass production, but appear
to be mainly attributable to higher soil moisture. Our results suggest that rising atmospheric CO2 may contribute more to the total greenhouse effect than is currently estimated because of its plant-mediated effects on soil
processes which may ultimately lead to increased N2O emissions from native grasslands.
Received: 11 September 1997 / Accepted: 20 March 1998 相似文献
12.
Leader dieback associated with B deficiency in P. radiata D. Don plantations was treated with borax applied at rates of 50, 100 and 150 kg ha−1. This initially increased B in foliage from 5 to 40, 80 and 110 μg g−1 respectively, and was followed by a rapid decline and stabilisation at around 25 μg g−1 for the duration of the study. Annual fluctuations in foliage B levels were strongly correlated with rainfall during the
preceding spring and summer. Uptake of N, P and K increased as a result of applied B and comparison of the distribution of
these nutrients in crowns of fertilized and unfertilised trees six years after application indicated continued uptake of these
nutrients probably as a result of improved root growth due to B. Foliage concentrations of B like N, P and K, increased in
young needles towards the upper crown and this, together with a decline in needle concentrations of B as foliage aged, indicated
some redistribution of B from older to new foliage. A limit of 5 μg g−1 was found below which little redistribution seems to occur.
Application of B prevented further leader dieback, improved apical dominance and height growth and increased volume production
by 25 m3 ha−1 at age 8 years. Differences between application rates of B were not significant in terms of growth. 相似文献
13.
Comparative study of periphyton community structure in long and short-hydroperiod Everglades marshes 总被引:1,自引:0,他引:1
The Florida Everglades is a mosaic of short and long-hydroperiod marshes that differ in the depth, duration, and timing of
inundation. Algae are important primary producers in widespread Everglades’ periphyton mats, but relationships of algal production
and community structure to hydrologic variability are poorly understood. We quantified differences in algal biomass and community
structure between periphyton mats in 5 short and 6 long-hydroperiod marshes in Everglades National Park (ENP) in October 2000.
We related differences to water depth and total phosphorus (TP) concentration in the water, periphyton and soils. Long and
short-hydroperiod marshes differed in water depth (73 cm vs. 13 cm), periphyton TP concentrations (172μg g−1 vs. 107 μg g−1, respectively) and soil TP (284 μg g−1 vs. 145 μg g−1). Periphyton was abundant in both marshes, with short-hydroperiod sites having greater biomass than long-hydroperiod sites
(2936 vs. 575 grams ash-free dry mass m−2). A total of 156 algal taxa were identified and separated into diatom (68 species from 21 genera) and “soft algae” (88 non-diatom
species from 47 genera) categories for further analyses. Although diatom total abundance was greater in long-hydroperiod mats,
diatom species richness was significantly greater in short- hydroperiod periphyton mats (62 vs. 47 diatom taxa). Soft algal
species richness was greater in long-hydroperiod sites (81 vs. 67 soft algae taxa). Relative abundances of individual taxa
were significantly different among the two site types, with soft algal distributions being driven by water depth, and diatom
distributions by water depth and TP concentration in the water and periphyton. Periphyton communities differ between short
and long-hydroperiod marshes, but because they share many taxa, alterations in hydroperiod could rapidly promote the alternate
community.
Electronic supplementary material Electronic supplementary material is available for this article at
and accessible for authorised users. 相似文献
14.
The effect of the fungicide, chlorothalonil, on vesicular-arbuscular mycorrhizal (VAM) symbiosis was studied in a greenhouse
using Leucaena leucocephala as test plant. Chlorothalonil was applied to soil at 0, 50, 100 and 200 μg g−1. The initial soil solution P levels were 0.003 μg mL−1 (sub-optimal) and 0.026 μg mL−1 (optimal). After 4 weeks, the sub-optimal P level was raised to 0.6 μg mL−1 (high). The soil was either uninoculated or inoculated with the VAM fungus, Glomus aggregatum. The fungicide reduced mycorrhizal colonization of roots, development of mycorrhizal effectiveness, shoot P concentration
and uptake and dry matter yields at all concentrations tested, although the highest inhibitory effect was noted as the concentration
of the fungicide was increased from 50 to 100 μg g−1. Phosphorus applied after four weeks tended to partially offset the deleterious effects of chlorothalonil in plants grown
in the inoculated and uninoculated soil which suggests that the fungicide was interfering with plant P uptake. The results
suggest that the use of chlorothalonil should be restricted to levels below 50 μg g−1 if the benefits of mycorrhizal symbiosis are to be expected.
Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 3464.
Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 3464. 相似文献
15.
Opposing effects of elevated CO2 and N deposition on Lymantria monacha larvae feeding on spruce trees 总被引:4,自引:0,他引:4
The effects of elevated atmospheric CO2 and increased wet N deposition on leaf quality and insect herbivory were evaluated in nine model ecosystems composed of 7-year-old
spruce trees (Picea abies) and three understorey species established on natural forest soil. Each model ecosystem was grown in a simulated montane
climate, and was exposed to one of three CO2 concentrations (280, 420, and 560 μl l−1), and to one of three levels of N deposition (0, 30, and 90 kg ha−1 year−1) for 3 years. In the 3rd year of the experiment second to third instars of the nun moth (Lymantria monacha) were allowed to feed directly on current-year needles of top canopy branches of each tree for 12 days. Specific leaf area
(SLA), water content, and N concentration decreased in needles exposed to elevated CO2, whereas the concentrations of starch, condensed tannins, and total phenolics increased. Increased N deposition had no significant
effect on SLA, and water content, but the concentrations of starch, condensed tannins, and total phenolics decreased, and
sugar and N concentrations increased. Despite higher relative consumption rates (RCRs) larvae consumed 33% less N per unit
larval biomass and per day at the two high CO2 treatments, compared to those feeding on 280 μl l−1-needles, but they maintained similar N accumulation rates due to increased N utilization efficiencies (NUE). However, over
the 12-day experimental period larvae gained less N overall and reached a 35% lower biomass in the two high-CO2 treatments compared to those at 280 μl l−1. The effects of increased N deposition on needle quality and insect performance were generally opposite to those of CO2 enrichment, but were lower in magnitude. We conclude that altered needle quality in response to elevated CO2 will impair the growth and development of L. monacha larvae. Increasing N deposition may mitigate these effects, which could lead to altered insect herbivore distributions depending
on regional patterns of N deposition.
Received: 8 June 1998 / Accepted: 27 October 1998 相似文献
16.
Luis Arigita Ma Jesús Cañal Ricardo Sánchez Tamés Aida González 《In vitro cellular & developmental biology. Plant》2010,46(3):312-322
In traditional in vitro culture, the low CO2 concentration inside the vessels restricts photosynthesis and necessitates the addition of sucrose to the culture medium
as the main energy source, thus bringing about changes in the absorption of mineral elements from the culture medium. In this
study, we investigated macronutrient absorption and sugar consumption in Actinidia deliciosa Chevalier Liang and Ferguson cv. Hayward (kiwi), cultured on medium supplemented with varying amounts of sucrose (0, 10,
and 20 g l−1) under both heterotrophy and autotrophy, flushed with different concentrations of CO2 (non-ventilation, 300, 600, and 2,000 μl l−1). In ventilated systems with 20 g l−1 of sucrose, sucrose absorption was less than under non-ventilation. The lowest rate of sucrose absorption was recorded when
the explants were cultured on medium supplemented with 20 g l−1 of sucrose and flushed with 600 μl l−1 CO2. Absorption of NO3
−, PO4
3−, and Mg2+ were high (maximum) at the end of the culture period (40 d) in explants flushed with 600 μl l−1 CO2 that have been cultured 20 d in the presence of sucrose and then transferred to a sucrose-free medium. These autotrophic
conditions promoted maximum plant growth in terms of both fresh and dry mass as well as the length and number of shoots and
leaves. The study shows that to maintain an optimum regime of mineral nutrition for prolonged culture of kiwi in vitro, an increased amount of these three ions should be supplemented in Murashige and Skoog’s medium. 相似文献
17.
Ciliate and bacterial densities and their link with eutrophication were studied in fourteen shallow lakes in northwest Spain.
Total phosphorus (TP) in these lakes varied between 30 μg l−1 and 925 μg l−1 and chlorophyll a concentration (chla) between 0.5 μg l−1 and 107 μg l−1. Bacterial abundance ranged from 1 × 106 to 14 × 106 cells ml−1, while ciliate abundance ranged from 0.6 cells ml−1 to 229 cells ml−1. Lakes were classified into three trophic types from their TP and chla concentrations. Bacterial abundance was significantly
correlated with trophic type, as well as with TP and with chla separately, whereas ciliate abundance was only correlated with
chla. No significant relationship could be established between bacterial and ciliate abundance across the trophic gradient.
A general pattern was observed in the ratios of bacterial abundance to TP and chla concentrations, of decreasing ratios with
increases in the nutrient loading. This pattern was not found for ciliates. The dominant zooplankton group in 13 of the 14
lakes studied was Rotifera, which accounted for a mean of 71% of total zooplankton abundance (41% of zooplankton biomass).
The positive correlation between bacteria and ciliates with this group, and the absence of any relationship with Cladocera
suggest that top down control by cladocerans was weaker in our lakes than previously shown in northern European shallow lakes.
Rotifers could be important predators of bacteria in the high-nutrient lakes of our study. Higher slopes of regressions on
bacterial abundance towards the hypertrophic range indicate that top-down control was weaker in our lakes than in northern
European shallow lakes. 相似文献
18.
Natural Occurrence of Mycotoxins in Staple Cereals from Ethiopia 总被引:1,自引:0,他引:1
The occurrence of mycotoxins in barley, sorghum, teff (Eragrostis tef) and wheat from Ethiopia has been studied. Samples were analyzed for aflatoxin B1 (AFB1), ochratoxin A (OTA), deoxynivalenol (DON), nivalenol (NIV) and zearalenone (ZEN) using high performance liquid chromatography
(HPLC) and for fumonisins (FUM) using enzyme linked immunosorbent assay (ELISA). AFB1 and OTA were detected in samples of
all the four crops. AFB1 was detected in 8.8% of the 352 samples analyzed at concentrations ranging from trace to 26 μg kg−1. OTA occurred in 24.3% of 321 samples at a mean concentration of 54.1 μg kg−1 and a maximum of 2106 μg kg−1. DON occurred in barley, sorghum and wheat at 40–2340 μg kg−1 with an overall incidence of 48.8% among the 84 mainly ‘suspect’ samples analyzed; NIV was co-analyzed with DON and was detected
at 40 μg kg−1 in a wheat sample and at 50, 380, and 490 μg kg−1 in three sorghum samples. FUM and ZEN occurred only in sorghum samples with low frequencies at concentrations reaching 2117
and 32 μg kg−1, respectively. The analytical results indicate higher mycotoxin contamination in sorghum, which could be related to the widespread
storage of sorghum grain in underground pits leading to elevated seed moisture contents. This is the first report on the occurrence
of OTA in teff. 相似文献
19.
The isolation, identification and quantification of exometabolites from culture media of the cyanobacterium Nostoc insulare are described. Besides the known exometabolite 4,4′-dihydroxybiphenyl (I), two more compounds, the β-carboline 9H-pyrido(3,4-b)indole
(norharmane, II) and N,N′-(4,5-dimethyl-1,2-phenylene)bis-acetamide (III), were discovered. Concentrations of all three compounds
in media and biomass of five 250 L cultures of N. insulare were determined. Culture medium values for I ranged between 200 and 1,250 μg L−1 (1.1–6.7 μmol L−1), for III between 115 and 390 μg L−1 (0.5–1.8 μmol L−1), whereas concentrations of II were conspicuously lower (2–16 μg L−1 or 0.014–0.094 μmol L−1). Amounts of III per volume of culture medium were about tenfold higher than in the biomass contained in an equal culture
volume. This difference is an indication for an active excretion of III. Amounts of I and II in biomass and media were of
no significant difference. In the neutral red uptake assay, I and II were found to be toxic against eukaryotic cells as follows:
I was of considerable cytotoxicity in concentrations from 1,000 to 10 mg L−1 and of lower cytotoxicity (causing a 27 % decrease of cell viability) in a concentration of 1,000 μg L−1, whereas II was merely of considerable cytotoxicity in concentrations from 1,000 to 100 mg L−1. Because of the cytotoxicity of I and because of the many known pharmacological effects of II there is a possibility that
a certain amount of risk to humans and livestock comes from cultures or even from biomass- free culture media of N. insulare. The natural function of the examined exometabolites is discussed. 相似文献
20.
Primary production of phytoplankton and secondary production of a daphnid and a chaoborid were studied in a small eutrophic
pond. The gross primary production of phytoplankton was 290 gC m−2 per 9 months during April–December. Regression analysis showed that the gross primary production was related to the incident
solar radiation and the chlorophylla concentration and not to either total phosphorus or total inorganic nitrogen concentration. The mean chlorophylla concentration (14.2 mg m−3), however, was about half the expected value upon phosphorus loading of this pond. The mean zooplankton biomass was 1.60
g dry weight m−2, of whichDaphnia rosea and cyclopoid copepods amounted to 0.69 g dry weight m−2 and 0.61 g dry weight m−2, respectively. The production ofD. rosea was high during May–July and October and the level for the whole 9 months was 22.6 g dry weight m−2.Chaoborus flavicans produced 10 complete and one incomplete cohorts per year. Two consecutive cohorts overlapped during the growing season. The
maximum density, the mean biomass, and the production were 19,100 m−2, 0.81 g dry weight m−2, and 11.7 g dry weight m−2yr−1, respectively. As no fish was present in this pond, the emerging biomass amounted to 69% of larval production. The production
ofC. flavicans larvae was high in comparison with zooplankton production during August–September, when the larvae possibly fed not only
on zooplankton but also algae. 相似文献