共查询到20条相似文献,搜索用时 15 毫秒
1.
Concentrations of sediment organic nitrogen, dissolved inorganic nitrogen (ammonium, nitrite and nitrate), and dissolved organic
nitrogen (DON) in sediments were measured at two sites in a eutrophic estuarine lagoon. One is a shallow aerobic site where
macrobenthos are abundant and the other is a deep anaerobic site devoid of macrobenthos. Four species of macrobenthos (Bivalvia:
Corbicula japonica, Annelida: Notomastus sp., Neanthes japonica and Oligochaeta sp.) were found in 8 sandy sediment cores
collected at a shallow site in three succcessive summers. DON (170–1500 μg atom N l-1) was the major constituent of dissolved
nitrogen with 10 times greater concentration than ammonium (55–180 μg atom N l-1) and 1000 times greater than nitrate (0.14–5.9
μg atom N l-1) and nitrite (0.21–1.4 μg atom N l-1). The ammonium content in anaerobic muddy sediments at the deep site (210–350
μg atom N l-1) was higher than in aerobic sandy sediments, whereas DON was higher in aerobic sediments than anaerobic sediments
(90–240 μg atom N l-1). In aerobic sediments, depth profiles of DIN were nearly constant whereas DON was mostly highest at
the surface. On the other hand, the increase of DON and ammonium was observed where macrobenthos was found. The occurrence
of macrobenthos and high content of DON and ammonium content in the layers of sediment may suggest the influence of macrobenthos
in the partitioning of nitrogen species through their motion and excretion.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Temporal and spatial distributions of dissolved organic carbon and nitrogen in two small lakes on the Southwestern China Plateau 总被引:6,自引:0,他引:6
Wen Li Fengchang Wu Congqiang Liu Pingqing Fu Jing Wang Yi Mei Liying Wang Jianyang Guo 《Limnology》2008,9(2):163-171
Temporal and spatial distributions of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), chlorophyll-a and inorganic nitrogen were investigated in two small mountainous lakes (Lake Hongfeng and Baihua), on the Southwestern China
Plateau, based on almost 2 years’ field observation. DOC concentrations ranged from 163 μM to 248 μM in Lake Hongfeng and
from 143 μM to 308 μM in Lake Baihua, respectively, during the study period. DON concentrations ranged from 7 μM to 26 μM
in Lake Hongfeng and from 14 μM to 47 μM in Lake Baihua. DOC showed vertical heterogeneity with higher concentrations in the
epilimnion than in the hypolimnion during the stratification period. The DON concentration profiles appeared to be more variable
than the DOC profiles. Apparent DON maxima occurred in the upper layer of water. In Lake Hongfeng, DOC concentration in the
surface water was highest at the end of spring and early summer. DON concentration was 2–5 μM higher in May 2003 and in June
2004 than in adjacent months. DOC and chlorophyll-a concentrations were significantly correlated (r = 0.79, P < 0.05). The period of highest concentrations of DOC in Lake Hongfeng was also the season of concentrated rainfall. Algae
activity and allochthonous input might result in an increase of DOC and DON concentrations together. In Lake Baihua, the maximum
concentrations of DOC and DON in the surface water occurred simultaneously in May 2003 and February 2004. DOC concentrations
were significantly correlated with DON (r = 0.90, P < 0.01), indicating the common sources. Allochthonous input, biological processes, stratification and mixing were the most
important factors controlling the distributions and cycling of dissolved organic matter (DOM) and inorganic nitrogen in these
two lakes. Inference from the corresponding vertical distributions of DOM and inorganic nitrogen indicated that DOM played
potential roles in the internal loading of nitrogen and metabolism in the water body in these small lakes. The carbon/nitrogen
(C/N) ratio showed a potential significance for tracing the source and biogeochemical processes of DOM in the lakes. These
results are of significance in the further understanding of biogeochemical cycling and environmental effects of DOM and nitrogen
in lake ecosystems. 相似文献
3.
Seasonal Variations of Dissolved Nitrogen and DOC:DON Ratios in an Intermittent Mediterranean Stream
Seasonal variations of dissolved inorganic nitrogen (DIN) (NO3–N and NH4–N) and dissolved organic nitrogen (DON) were determined in Fuirosos, an intermittent stream draining an unpolluted Mediterranean
forested catchment (10.5 km2) in Catalonia (Spain). The influence of flow on streamwater concentrations and seasonal differences in quality and origin
of dissolved organic matter, inferred from dissolved organic carbon to nitrogen ratios (DOC:DON ratios), were examined. During
baseflow conditions, nitrate and ammonium had opposite behaviour, probably controlled by biological processes such as vegetation
uptake and mineralization activity. DON concentrations did not have a seasonal trend. During storms, nitrate and DON increased
by several times but discharge was not a good predictor of nutrient concentrations. DOC:DON ratios in streamwater were around
26, except during the months following drought when DOC:DON ratios ranged between 42 and 20 during baseflow and stormflow
conditions, respectively. Annual N export during 2000–2001 was 70 kg km−1 year−1, of which 75% was delivered during stormflow. The relative contribution of nitrogen forms to the total annual export was
57, 35 and 8% as NO3–N, DON and NH4–N, respectively. 相似文献
4.
The Long-term Effects of Disturbance on Organic and Inorganic Nitrogen Export in the White Mountains, New Hampshire 总被引:22,自引:8,他引:14
Traditional biogeochemical theories suggest that ecosystem nitrogen retention is controlled by biotic N limitation, that stream
N losses should increase with successional age, and that increasing N deposition will accelerate this process. These theories
ignore the role of dissolved organic nitrogen (DON) as a mechanism of N loss. We examined patterns of organic and inorganic
N export from sets of old-growth and historically (80–110 years ago) logged and burned watersheds in the northeastern US,
a region of moderate, elevated N deposition. Stream nitrate concentrations were strongly seasonal, and mean (± SD) nitrate
export from old-growth watersheds (1.4 ± 0.6 kg N ha−1 y−1) was four times greater than from disturbed watersheds (0.3 ± 0.3 kg N ha−1 y−1), suggesting that biotic control over nitrate loss can persist for a century. DON loss averaged 0.7 (± 0.2) kg N ha−1 y−1 and accounted for 28–87% of total dissolved N (TDN) export. DON concentrations did not vary seasonally or with successional
status, but correlated with dissolved organic carbon (DOC), which varied inversely with hardwood forest cover. The patterns
of DON loss did not follow expected differences in biotic N demand but instead were consistent with expected differences in
DOC production and sorption. Despite decades of moderate N deposition, TDN export was low, and even old-growth forests retained
at least 65% of N inputs. The reasons for this high N retention are unclear: if due to a large capacity for N storage or biological
removal, N saturation may require several decades to occur; if due to interannual climate variability, large losses of nitrate
may occur much sooner.
Received 27 April 1999; accepted 30 May 2000. 相似文献
5.
Rubén J. Lara Sucharit B. Neogi Mohammad S. Islam Zahid H. Mahmud Shafiqul Islam Debasish Paul Biniam B. Demoz Shinji Yamasaki Gopinath B. Nair Gerhard Kattner 《Wetlands Ecology and Management》2011,19(1):109-119
Wetland dynamics are probably linked to cholera endemicity in South Asia. We focus on links between Vibrio cholerae abundance, chitin content and suspended particle load in size fractions of suspended particulate matter (SPM) along the salinity
gradient of Sunderban mangrove waters. SPM decreased downstream, while salinity increased from 0.2 to 4. Particulate organic
carbon (90 ± 25 μM) and nitrogen (9.1 ± 3.3 μM) highly correlated with SPM and turbidity, suggesting a significant contribution
of fine particles to organic matter. Total chitin ranged 1–2 mg/l and decreased downstream. The distribution among size fractions
of SPM, chitin and V. cholerae O1 (the bacterial serogroup mainly associated with cholera epidemics) was similar, with ~98% of the total in the fraction
<20 μm. In comparison, the number of V. cholerae O1 attached to zooplankton and microplankton size classes >20 μm was almost negligible, in contrast to usual assumptions.
Thus, microdetritus, nanoplankton and fungal cells in size classes <20 μm represent a chitinaceous substrate on which V. cholerae can grow and survive. Total bacteria, cultivable vibrios and V. cholera O1 increased 5–10 times downstream, together with salinity and nitrite concentration. Overall, nitrate and silicate concentrations
were relatively constant (>22 μM N and 100 μM Si). However, nitrite increased ~9 times in the outer sector, reaching ~1.2 μM
N, probably as a result of increased abundance of nitrate-reducing vibrios. A characterization of Vibrio habitats that takes account of the presence of nitrate-reducing bacteria could improve the understanding of both mangrove
nitrogen cycling and cholera seasonality. 相似文献
6.
7.
Y. Tanaka T. Miyajima A. Watanabe K. Nadaoka T. Yamamoto H. Ogawa 《Coral reefs (Online)》2011,30(2):533-541
Dissolved organic matter (DOM) concentrations in a fringing coral reef were measured for both carbon and nitrogen with the
analytical technique of high-temperature catalytic oxidation. Because of high precision of the analytical system, not only
the concentrations of dissolved organic carbon and nitrogen (DOC and DON, respectively) but the C:N ratio was also determined
from the distribution of DOC and DON concentrations. The observed concentrations of DOC and DON ranged 57–76 and 3.8–5.6 μmol l−1, respectively. The C:N ratios of the DOM that was produced on the reef flat were very similar between seagrass- and coral-dominated
areas; the C:N ratio was 10 on average. The C:N ratio of DOM was significantly higher than that of particulate organic matter
(POM) that was produced on the reef flat. Production rates of DOC were measured on the reef flat during stagnant periods and
accounted for 3–7% of the net primary production, depending on the sampling site. The production rate of DON was estimated
to be 10–30% of the net uptake of dissolved inorganic N in the reef community. Considering that the DOM and POM concentrations
were not correlated with each other, a major source of the reef-derived DOM may be the benthic community and not POM such
as phytoplankton. It was concluded that a widely distributed benthic community in the coral reef released C-rich DOM to the
overlying seawater, conserving N in the community. 相似文献
8.
Patterns in the Chemical Fractionation of Organic Nitrogen in Rocky Mountain Streams 总被引:8,自引:2,他引:6
The intraannual dynamics of particulate organic nitrogen (PON) and two fractions of dissolved organic nitrogen (DON) were investigated in two Rocky Mountain streams draining watersheds with low rates of N deposition. Organic nitrogen accounted for over 60% of the total annual nitrogen export and consisted mostly of DON. Nitrate peaked during winter months and declined considerably during the growing season (less than 10 µg/L) suggesting the importance of biotic uptake. Concentrations of PON, total DON, and two DON fractions (humic and non-humic) peaked during spring runoff and were positively related to discharge, indicating hydrologic influence. Total DON and its two fractions showed significant inverse relationships to nitrate, indicating that DON and nitrate followed different intraannual patterns. Despite its seasonal fluctuations in concentration, PON showed a consistent carbon–nitrogen (C:N) ratio suggesting that it was relatively uniform in composition. Fractionation studies indicated that DON was primarily of non-humic origin, whereas dissolved organic carbon (DOC) was mainly derived from humic sources. The two DON fractions differed from each other in seasonal patterns of concentration and C:N ratio. The proportion of humic DON increased during snowmelt, and there were diverging seasonal patterns in the C:N ratio of the two fractions implying variations in bioavailability. Although organic nitrogen is commonly treated as a single pool in ecological studies, our results indicated that DON consists of fractions that undergo large intraannual changes in proportions and chemical composition. Treatment of DON as a single pool may be misleading from the viewpoint of understanding ecosystem processes directly related to changes in its sources and biological reactivity. 相似文献
9.
《Harmful algae》2014
Diatom blooms in Thau lagoon are always related to rain events leading to inputs of inorganic nutrients such as phosphate, ammonium and nitrate through the watershed with time lags of about 1 week. In contrast, blooms of Alexandrium catenella/tamarense can occur following periods of 3 weeks without precipitation and no significant input of conventional nutrients such as nitrate and phosphate. Field results also indicate a significant drop (from 22–25 to 15–16 μM over 3 days) in dissolved organic nitrogen (DON) at the bloom peak, as well as a significant inverse relationship between A. catenella/tamarense cell density and DON concentrations that is not apparent for diatom blooms. Such dinoflagellate blooms are also associated with elevated (6–9 μM) ammonium concentrations, a curious feature also observed by other investigators, possibly the results of ammonium excretion by this organism during urea or other organic nitrogen assimilation.The potential use of DON by this organism represents short cuts in the nitrogen cycle between plants and nutrients and requires a new model for phytoplankton growth that is different from the classical diatom bloom model. In contrast to such diatom blooms that are due to conventional (nitrate, phosphate) nutrient pulses, Alexandrium catenella/tamarense blooms on the monthly time scale are due to organic nutrient enrichment, a feature that allows net growth rates of about 1.3 d−1, a value higher than that generally attributed to such organisms. 相似文献
10.
Klaus Martin Meiners S. Papadimitriou D. N. Thomas L. Norman G. S. Dieckmann 《Polar Biology》2009,32(7):1055-1065
Physical, biogeochemical and photosynthetic parameters were measured in sea ice brine and ice core bottom samples in the north-western
Weddell Sea during early spring 2006. Sea ice brines collected from sackholes were characterised by cold temperatures (range
−7.4 to −3.8°C), high salinities (range 61.4–118.0), and partly elevated dissolved oxygen concentrations (range 159–413 μmol kg−1) when compared to surface seawater. Nitrate (range 0.5–76.3 μmol kg−1), dissolved inorganic phosphate (range 0.2–7.0 μmol kg−1) and silicic acid (range 74–285 μmol kg−1) concentrations in sea ice brines were depleted when compared to surface seawater. In contrast, NH4
+ (range 0.3–23.0 μmol kg−1) and dissolved organic carbon (range 140–707 μmol kg−1) were enriched in the sea ice brines. Ice core bottom samples exhibited moderate temperatures and brine salinities, but high
algal biomass (4.9–435.5 μg Chl a l−1 brine) and silicic acid depletion. Pulse amplitude modulated fluorometry was used for the determination of the photosynthetic
parameters F
v/F
m, α, rETRmax and E
k. The maximum quantum yield of photosystem II, F
v/F
m, ranged from 0.101 to 0.500 (average 0.284 ± 0.132) and 0.235 to 0.595 (average 0.368 ± 0.127) in the sea ice internal and
bottom communities, respectively. The fluorometric measurements indicated medium ice algal photosynthetic activity both in
the internal and bottom communities of the sea ice. An observed lack of correlation between biogeochemical and photosynthetic
parameters was most likely due to temporally and spatially decoupled physical and biological processes in the sea ice brine
channel system, and was also influenced by the temporal and spatial resolution of applied sampling techniques. 相似文献
11.
Federico A. Gutiérrez-Miceli Lourdes Arias Nicolás Juarez-Rodríguez Miguel Abud-Archila Aldo Amaro-Reyes Luc Dendooven 《In vitro cellular & developmental biology. Plant》2010,46(1):57-63
This paper reports on the optimum concentrations of naphthalene acetic acid (NAA) and 6-benzyladenine (BA) to stimulate callus
growth and NAA; kinetin and silver nitrate (AgNO3) for callus redifferentiation in Dianthus caryophyllus L. Meristems were excised and placed in MS medium with 30 g l−1 sucrose and 9.0 μM 2,4-d. Callus clusters were transferred to MS medium containing NAA (0, 1.7, 3.3, and 5.0 μM) and BA (0, 1.7, 3.3, and 5.0 μM)
for proliferation and to MS medium with 30 g l−1 sucrose, 2.5 g l−1 phytagel, kinetin (0, 33, and 66 μM); NAA (0, 7.95, and 15.9 μM) and AgNO3 (0, 23.54 and 47.08 μM) for shoot and root induction. Treatments were applied according to a Box–Behnken design. After callus
growth and redifferentiation, plants were incubated in the greenhouse at 18 ± 2°C for 4 wk and at 20–26°C for 4 wk. Finally,
plants were changed to near-commercial greenhouse conditions with different day (30–35°C) and night (16–24°C) temperatures.
Results showed better callus growth at higher NAA concentrations. A maximum callus weight was found with 5.0 μM NAA but without
BA. A maximum of 78% calluses with shoots was obtained with 15.9 μM NAA, 47.08 μM AgNO3, and 0.74 μM kinetin and 58% with roots with 15.7 μM NAA and 47.08 μM AgNO3, but without kinetin. The shoots obtained showed little hyperhydricity. Vigorous plants were obtained after gradual acclimatization
with an 80% survival rate under nursery conditions. 相似文献
12.
Mechanisms underlying export of N from high-elevation catchments during seasonal transitions 总被引:4,自引:4,他引:0
James O. Sickman Al Leydecker Cecily C.Y. Chang Carol Kendall John M. Melack Delores M. Lucero Joshua Schimel 《Biogeochemistry》2003,64(1):1-24
Mechanisms underlying catchment export of nitrogen (N) during seasonal transitions (i.e., winter to spring and summer to autumn) were investigated in high-elevation catchments of the Sierra Nevada using stable isotopes of nitrate and water, intensive monitoring of stream chemistry and detailed catchment N-budgets. We had four objectives: (1) determine the relative contribution of snowpack and soil nitrate to the spring nitrate pulse, (2) look for evidence of biotic control of N losses at the catchment scale, (3) examine dissolved organic nitrogen ( DON) export patterns to gain a better understanding of the biological and hydrological controls on DON loss, and (4) examine the relationship between soil physico-chemical conditions and N export. At the Emerald Lake watershed, nitrogen budgets and isotopic analyses of the spring nitrate pulse indicate that 50 to 70% of the total nitrate exported during snowmelt (ca. April to July) is derived from catchment soils and talus; the remainder is snowpack nitrate. The spring nitrate pulse occurred several weeks after the start of snowmelt and was different from export patterns of less biologically labile compounds such as silica and DON suggesting that: (1) nitrate is produced and released from soils only after intense flushing has occurred and (2) a microbial N-sink is operating in catchment soils during the early stages of snowmelt. DON concentrations varied less than 20–30% during snowmelt, indicating that soil processes tightly controlled DON losses. 相似文献
13.
Christine L. Goodale Steven A. Thomas Guinevere Fredriksen Emily M. Elliott Kathryn M. Flinn Thomas J. Butler M. Todd Walter 《Biogeochemistry》2009,93(3):197-218
Atmospheric deposition contributes a large fraction of the annual nitrogen (N) input to the basin of the Susquehanna River,
a river that provides two-thirds of the annual N load to the Chesapeake Bay. Yet, there are few measurements of the retention
of atmospheric N in the Upper Susquehanna’s forested headwaters. We characterized the amount, form (nitrate, ammonium, and
dissolved organic nitrogen), isotopic composition (δ15N- and δ18O-nitrate), and seasonality of stream N over 2 years for 7–13 catchments. We expected high rates of N retention and seasonal
nitrate patterns typical of other seasonally snow-covered catchments: dormant season maxima and growing season minima. Coarse
estimates of N export indicated high rates of inorganic N retention (>95%), yet streams had unexpected seasonal nitrate patterns,
with summer peaks (14–96 μmol L−1), October crashes (<1 μmol L−1), and modest rebounds during the dormant season (<1–20 μmol L−1). Stream δ18O-nitrate values indicated microbial nitrification as the primary source of stream nitrate, although snowmelt or other atmospheric
source contributed up to 47% of stream nitrate in some March samples. The autumn nitrate crash coincided with leaffall, likely
due to in-stream heterotrophic uptake of N. Hypothesized sources of the summer nitrate peaks include: delayed release of nitrate
previously flushed to groundwater, weathering of geologic N, and summer increases in net nitrate production. Measurements
of shale δ15N and soil-, well-, and streamwater nitrate within one catchment point toward a summer increase in soil net nitrification
as the driver of this pattern. Rather than seasonal plant demand, processes governing the seasonal production, retention,
and transport of nitrate in soils may drive nitrate seasonality in this and many other systems. 相似文献
14.
Nitrate accumulation in leaves of vegetation of a forested ecosystem receiving high amounts of atmospheric ammonium sulfate 总被引:2,自引:0,他引:2
Vegetation of an acid woodland, receiving an atmospheric ammonium input of about 3 kmol (40 kg N) per hectare per year, was
analyzed on the content of organic nitrogen, ammonium and nitrate. A high nitrate content (50–320 μmol g−1 dry weight) was found in bird-cherry, black-berry and bracken, whereas only low amounts (up to 2 μmol g−1 dry weight) of nitrate were present in mountain-ash, hazel and the two dominant tree species oak and birch. The impact of
this nitrate uptake and nitrate accumulation on soil pH and autotrophic nitrification is discussed. 相似文献
15.
Concentrations of deoxynivalenol (DON) and deepoxy deoxynivalenol (DOM-1) in animal blood are important parameters for studies
in toxicology and biological detoxification of DON. Clean-up methods, using either immunoaffinity chromatography (IAC) or
solid phase extraction (SPE), were compared in order to determine the free form of DON or DOM-1 and the sum amount (free form
plus glucuronide conjugated form of DON or DOM-1), respectively, in swine serum. Detection was achieved by high performance
liquid chromatography with ultraviolet detection (HPLC-UV). Compared with the SPE-HPLC method, the IAC-HPLC method provided
lower quantitation limit (DON: 18 vs 42 ng/ml; DOM-1: 21 vs 30 ng/ml) and higher recoveries (DON: 93.4–102.7% vs 63.7–85.3%;
DOM-1: 85.5–91.1% vs 68.0–82.6%). Compared with previously published methods, the developed IAC-HPLC method removed analytical
interferences from swine serum in one quick and easy step, and eliminated steps of extraction with organic solvent and/or
pre-purification using SPE cartridges. This IAC-HPLC method was used to analyze swine serum samples collected from pigs that
were evaluated in a feeding trial of a microbiological detoxification of DON. No DON or DOM-1 were detected in serum samples
from pigs given a toxin-free diet or a microbial control diet. In serum samples from pigs given a DON diet (5 mg/kg of DON),
free form DON and sum free DON + conjugated DON were 38.8 ± 13.7 and 49.8 ± 14.1 ng/ml, respectively. In serum samples from
those given a detoxified-DON diet (DON was transformed to DOM-1), free form DOM-1 was detected but not quantified, and the
sum DOM-1 was found as 47.5 ± 6.3 ng/ml. 相似文献
16.
Fate and Transport of Organic Nitrogen in Minimally Disturbed Montane Streams of Colorado,USA 总被引:1,自引:0,他引:1
In two montane watersheds that receive minimal deposition of atmospheric nitrogen, 15–71% of dissolved organic nitrogen (DON)
was bioavailable in stream water over a 2-year period. Discharge-weighted concentrations of bulk DON were between 102 and
135 μg/l, and the C:N ratio differed substantially between humic and non-humic fractions of DON. Approximately 70% of DON export
occurred during snowmelt, and 40% of that DON was biologically available to microbes in stream sediments. Concentrations of
bioavailable DON in stream water were 2–16 times greater than dissolved inorganic nitrogen (DIN) during the growing season,
and bioavailable DON was depleted within 2–14 days during experimental incubations. Uptake of DON was influenced by the concentration
of inorganic N in stream water, the concentration of non-humic DON in stream water, and the C:N ratio of the non-humic fraction
of dissolved organic matter (DOM). Uptake of DON declined logarithmically as the concentration of inorganic N in stream water
increased. Experimental additions of inorganic N also caused a decline in uptake of DON and net production of DON when the
C:N ratio of non-humic DOM was high. This study indicates that the relative and absolute amount of bioavailable DON can vary
greatly within and across years due to interactions between the availability of inorganic nutrients and composition of DOM.
DOM has the potential to be used biotically at a high rate in nitrogen-poor streams, and it may be generated by heterotrophic
microbes when DIN and labile DOM with low relative nitrogen content become abundant. 相似文献
17.
Andreas Gutzwiller 《Mycotoxin Research》2010,26(3):211-215
A diet contaminated with 2.8 mg deoxynivalenol (DON)/kg was fed at 6 kg per day to 32 mycotoxin-exposed pluriparous sows (M)
during lactation. The 31 control sows (C) received 6 kg of an uncontaminated diet. Although more contaminated diet was refused
(P = 0.05), DON exposure had no effect (P > 0.1) on body weight loss of the sows during lactation (M: 27.9 ± 12.3 kg; C: 29.7 ± 10.2 kg), the number of weaned piglets
(M: 9.8 ± 1.4; C: 9.7 ± 1.6) and their daily weight gain (M: 266 ± 70 g; C: 272 ± 64 g). Several sows were culled after weaning
for reasons unrelated to the experiment. Compared with the remaining 21 C sows, the remaining 26 M sows had an identical interval
between weaning and the next farrowing (M: 120 ± 1 days; C: 120 ± 1 days) and a similar litter size (M: 14.5 ± 2.7; C: 14.9 ± 3.0;
P > 0.10). The daily intake of 17 mg DON during lactation thus did not affect the reproductive performance of the sows. 相似文献
18.
Renata Matraszek 《Acta Physiologiae Plantarum》2008,30(3):361-370
The author studied the effect of different nickel concentrations (0, 0.4, 40 and 80 μM Ni) on the nitrate reductase (NR) activity
of New Zealand spinach (Tetragonia expansa Murr.) and lettuce (Lactuca sativa L. cv. Justyna) plants supplied with different nitrogen forms (NO3
−–N, NH4
+–N, NH4NO3). A low concentration of Ni (0.4 μM) did not cause statistically significant changes of the nitrate reductase activity in
lettuce plants supplied with nitrate nitrogen (NO3
−–N) or mixed (NH4NO3) nitrogen form, but in New Zealand spinach leaves the enzyme activity decreased and increased, respectively. The introduction
of 0.4 μM Ni in the medium containing ammonium ions as a sole source of nitrogen resulted in significantly increased NR activity
in lettuce roots, and did not cause statistically significant changes of the enzyme activity in New Zealand spinach plants.
At a high nickel level (Ni 40 or 80 μM), a significant decrease in the NR activity was observed in New Zealand spinach plants
treated with nitrate or mixed nitrogen form, but it was much more marked in leaves than in roots. An exception was lack of
significant changes of the enzyme activity in spinach leaves when plants were treated with 40 μM Ni and supplied with mixed
nitrogen form, which resulted in the stronger reduction of the enzyme activity in roots than in leaves. The statistically
significant drop in the NR activity was recorded in the aboveground parts of nickel-stressed lettuce plants supplied with
NO3
−–N or NH4NO3. At the same time, there were no statistically significant changes recorded in lettuce roots, except for the drop of the
enzyme activity in the roots of NO3
−-fed plants grown in the nutrient solution containing 80 μM Ni. An addition of high nickel doses to the nutrient solution
contained ammonium nitrogen (NH4
+–N) did not affect the NR activity in New Zealand spinach plants and caused a high increase of this enzyme in lettuce organs,
especially in roots. It should be stressed that, independently of nickel dose in New Zealand spinach plants supplied with
ammonium form, NR activity in roots was dramatically higher than that in leaves. Moreover, in New Zealand spinach plants treated
with NH4
+–N the enzyme activity in roots was even higher than in those supplied with NO3
−–N. 相似文献
19.
Sampling of the central region of the North Sea was carried out to study the spatial and seasonal changes of dissolved and
particulate organic C (DOC and POC, respectively). The surface waters were collected during four cruises over a year (Autumn
2004–Summer 2005). DOC and POC concentrations were measured using high temperature catalytic oxidation methods. The surface
water concentrations of DOC and POC were spatially and temporally variable. There were significantly different concentrations
of DOC and POC between the inshore and offshore waters in winter and summer only, with no clear trend in autumn and spring.
Highest mean concentrations of DOC were measured in spring with lower and similar mean concentrations for other seasons. POC
showed a clear seasonal cycle throughout the year with highest surface mean concentrations found in autumn and spring, but
lowest in winter and summer. The DOC distributions during autumn and spring were strongly correlated with chlorophyll suggesting
extracellular release from phytoplankton was an important DOC source during these two seasons. The lower concentrations of
DOC in summer were probably due to the heterotrophic uptake of labile DOC. The seasonal changes in the C:N molar ratios of
surface DOM (dissolved organic matter) resulted in higher mean C:N molar ratios in spring and lower ratios in winter. These
high ratios may indicate nutrient limitation of heterotrophic uptake immediately after the spring bloom. There is limited
data available for DOC cycling in these productive shelf seas and these results show that DOC is a major component of the
C cycle with partial decoupling of the DOC and DON cycling in the central North Sea during the spring bloom.
Handling editor: Luigi Naselli-Flores 相似文献
20.
Landscape Controls on Organic and Inorganic Nitrogen Leaching across an Alpine/Subalpine Ecotone,Green Lakes Valley,Colorado Front Range 总被引:5,自引:0,他引:5
Here we report measurements of organic and inorganic nitrogen (N) fluxes from the high-elevation Green Lakes Valley catchment
in the Colorado Front Range for two snowmelt seasons (1998 and 1999). Surface water and soil samples were collected along
an elevational gradient extending from the lightly vegetated alpine to the forested subalpine to assess how changes in land
cover and basin area affect yields and concentrations of ammonium-N (NH4-N), nitrate-N (NO3-N), dissolved organic N (DON), and particulate organic N (PON). Streamwater yields of NO3-N decreased downstream from 4.3 kg ha−1 in the alpine to 0.75 kg ha−1 at treeline, while yields of DON were much less variable (0.40–0.34 kg ha−1). Yields of NH4-N and PON were low and showed little variation with basin area. NO3-N accounted for 40%–90% of total N along the sample transect and was the dominant form of N at all but the lowest elevation
site. Concentrations of DON ranged from approximately 10% of total N in the alpine to 45% in the subalpine. For all sites,
volume-weighted mean concentrations of total dissolved nitrogen (TDN) were significantly related to the DIN:DON ratio (R
2 = 0.81, P < 0.001) Concentrations of NO3-N were significantly higher at forested sites that received streamflow from the lightly vegetated alpine reaches of the catchment
than in a control catchment that was entirely subalpine forest, suggesting that the alpine may subsidize downstream forested
systems with inorganic N. KCl-extractable inorganic N and microbial biomass N showed no relationship to changes in soil properties
and vegetative cover moving downstream in catchment. In contrast, soil carbon–nitrogen (C:N) ratios increased with increasing
vegetative cover in catchment and were significantly higher in the subalpine compared to the alpine (P < 0.0001) Soil C:N ratios along the sample transect explained 78% of the variation in dissolved organic carbon (DOC) concentrations
and 70% of the variation in DON concentrations. These findings suggest that DON is an important vector for N loss in high-elevation
ecosystems and that streamwater losses of DON are at least partially dependent on catchment soil organic matter stoichiometry.
Received 26 July 2001; accepted 6 May 2002. 相似文献