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1.
The influence of land use on potential fates of nitrate (NO3
−) in stream ecosystems, ranging from denitrification to storage in organic matter, has not been documented extensively. Here,
we describe the Pacific Northwest component of Lotic Intersite Nitrogen eXperiment, phase II (LINX II) to examine how land-use
setting influences fates of NO3
− in streams. We used 24 h releases of a stable isotope tracer (15NO3-N) in nine streams flowing through forest, agricultural, and urban land uses to quantify NO3
− uptake processes. NO3
− uptake lengths varied two orders of magnitude (24–4247 m), with uptake rates (6.5–158.1 mg NO3-N m−2 day−1) and uptake velocities (0.1–2.3 mm min−1) falling within the ranges measured in other LINX II regions. Denitrification removed 0–7% of added tracer from our streams.
In forest streams, 60.4 to 77.0% of the isotope tracer was exported downstream as NO3
−, with 8.0 to 14.8% stored in wood biofilms, epilithon, fine benthic organic matter, and bryophytes. Agricultural and urban
streams with streamside forest buffers displayed hydrologic export and organic matter storage of tracer similar to those measured
in forest streams. In agricultural and urban streams with a partial or no riparian buffer, less than 1 to 75% of the tracer
was exported downstream; much of the remainder was taken up and stored in autotrophic organic matter components with short
N turnover times. Our findings suggest restoration and maintenance of riparian forests can help re-establish the natural range
of NO3
− uptake processes in human-altered streams. 相似文献
2.
Shifts in allochthonous input and autochthonous production in streams along an agricultural land-use gradient 总被引:2,自引:0,他引:2
Elizabeth M. Hagen Matthew E. McTammany Jackson R. Webster Ernest F. Benfield 《Hydrobiologia》2010,655(1):61-77
Relative contributions of allochthonous inputs and autochthonous production vary depending on terrestrial land use and biome.
Terrestrially derived organic matter and in-stream primary production were measured in 12 headwater streams along an agricultural
land-use gradient. Streams were examined to see how carbon (C) supply shifts from forested streams receiving primarily terrestrially
derived C to agricultural streams, which may rely primarily on C derived from algal productivity. We measured allochthonous
input, chlorophyll a concentration, and periphyton biomass in each stream, and whole-stream metabolism in six streams. Our results suggest a threshold
between moderate- and heavy-agriculture land uses in which terrestrially derived C is replaced by in-stream algal productivity
as the primary C source for aquatic consumers. A shift from allochthonous to autochthonous production was not evident in all
heavy-agriculture streams, and only occurred in heavy-agriculture streams not impacted by livestock grazing. We then compared
our findings to rates of allochthonous input and GPP in streams with minimal human influences in multiple biomes to assess
how land-use practices influence C sources to stream ecosystems. The proportion of C derived from allochthonous versus autochthonous
sources to heavy-agriculture streams was most similar to grassland and desert streams, while C sources to forested, light-,
and moderate-agriculture streams were more similar to deciduous and montane coniferous forest streams. We show that C source
to streams is dependent on land use, terrestrial biome, and degradation of in-stream conditions. Further, we suggest that
within a biome there seems to be a compensation such that total C input is nearly equal whether it is from allochthonous or
autochthonous sources. 相似文献
3.
Jes Jessen Rasmussen Annette Baattrup-Pedersen Tenna Riis Nikolai Friberg 《Aquatic Ecology》2011,45(2):231-242
We surveyed macrophyte community structure and measured community metabolism and nutrient uptake along a temperature gradient
(9.7–17.4°C) in four Icelandic streams influenced by geothermal heating. The study streams are part of the geothermal area
in Hengill that is uniquely characterised by streams with comparable water chemistry despite the geothermal influence. Stream
metabolism was studied applying the diurnal upstream–downstream dissolved oxygen change technique. Nutrient uptake was studied
by adding solutions of nitrogen and phosphorus together with a conservative tracer. Rates of primary production (GPP) and
uptake of nitrate–N and phosphate-P increased with increasing stream temperature. GPP was 20 times higher (up to 12.99 g O2 m−2 day−1) and rates of nutrient uptake were up to 30-times higher (up to 22.99, 13.31 and 7.94 mg m−2 h−1 for ammonium, nitrate and phosphate, respectively) in the warmest streams compared with the coldest. Furthermore, macrophytes,
when present, were strongly controlling ecosystem processes. Our study implies that temperature may affect stream ecosystem
processes both directly (i.e. physiologically) and indirectly (i.e. by changing other structural parameters). 相似文献
4.
Urban streams often contain elevated concentrations of nitrogen (N) which can be amplified in systems receiving effluent from
wastewater treatment plants (WWTP). In this study, we evaluated the importance of denitrification in a stream draining urban
Greensboro, NC, USA, using two approaches: (1) natural abundance of 15N–NO3− in conjunction with background NO3−–N concentrations along a 7 km transect downstream of a WWTP; and (2) C2H2 block experiments at three sites and at three habitat types within each site. Overall lack of a longitudinal pattern of δ15N–NO3− and NO3−–N, combined with high concentrations of NO3−–N suggested that other factors were controlling NO3−–N flux in the study transect. However, denitrification did appear to be significant along one portion of the transect. C2H2 block experiments showed that denitrification rates were much higher downstream of the WWTP compared to upstream, and showed
that denitrification rates were highest in erosional and depositional areas downstream of the WWTP and in erosional areas
upstream of the plant. Thus, the combination of the two methods for evaluating denitrification provided more insight into
the spatial dynamics of denitrification activity than either approach alone. Denitrification appeared to be a significant
sink for NO3−–N upstream of the WWTP, but not downstream. Approximately 46% of the total NO3−–N load was removed via denitrification in the upstream, urban section of the stream, while only 2.3% of NO3−–N was lost downstream of the plant. This result suggests that controlling NO3−–N loading from the plant could result in considerable improvement of downstream water quality. 相似文献
5.
We assessed the effect of whole-stream nitrate enrichment on decomposition of three substrates differing in nutrient quality
(alder and oak leaves and balsa veneers) and associated fungi and invertebrates. During the 3-month nitrate enrichment of
a headwater stream in central Portugal, litter was incubated in the reference site (mean NO3-N 82 μg l−1) and four enriched sites along the nitrate gradient (214–983 μg NO3-N l−1). A similar decomposition experiment was also carried out in the same sites at ambient nutrient conditions the following
year (33–104 μg NO3-N l−1). Decomposition rates and sporulation of aquatic hyphomycetes associated with litter were determined in both experiments,
whereas N and P content of litter, associated fungal biomass and invertebrates were followed only during the nitrate addition
experiment. Nitrate enrichment stimulated decomposition of oak leaves and balsa veneers, fungal biomass accrual on alder leaves
and balsa veneers and sporulation of aquatic hyphomycetes on all substrates. Nitrate concentration in stream water showed
a strong asymptotic relationship (Michaelis–Menten-type saturation model) with temperature-adjusted decomposition rates and
percentage initial litter mass converted into aquatic hyphomycete conidia for all substrates. Fungal communities did not differ
significantly among sites but some species showed substrate preferences. Nevertheless, certain species were sensitive to nitrogen
concentration in water by increasing or decreasing their sporulation rate accordingly. N and P content of litter and abundances
or richness of litter-associated invertebrates were not affected by nitrate addition. It appears that microbial nitrogen demands
can be met at relatively low levels of dissolved nitrate, suggesting that even minor increases in nitrogen in streams due
to, e.g., anthropogenic eutrophication may lead to significant shifts in microbial dynamics and ecosystem functioning.
Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . 相似文献
6.
The kinetics of ammonium and nitrate uptake by young rice plants 总被引:13,自引:0,他引:13
Summary An important process which affects the fate of fertilizer nitrogen (N) applied to a rice crop is crop N uptake. This uptake
rate is controlled by many factors including the N-ion species and its concentration. In this study the relation between N
concentration at the root surface and N uptake was characterized using Michaelis-Menten kinetics.
The equation considers two parameters, Vmax and Km, which are measures of the maximum rate of uptake and the affinity of the
uptake sites for the nutrient, respectively.
Uptake rates of intact rice plants growing in a continuously flowing nutrient solution system were fitted to the Michaelis-Menten
model using a weighted regression analysis. For NH4−N the Km values for 4- and 9-week-old rice plants indicated a high affinity for the ammonium ions relative to concentrations
reported for rice soils after fertilization. The Vmax values expressed on a unit-root-mass basis decreased with plant age,
indicating a reduction in the average density of uptake sites on the root surface.
The kinetics of NO3−N uptake was similar to that of NH4−N when NO3−N was the only N source. However, if NH4−N and NO3−N were present simultaneously in the solution the Vmax for the uptake of NO3−N was severely reduced, while the Km was affected very little. This inhibition appears to be noncompetitive.
Fertilization of young rice plants leading to concentration of N at the root surface above approximately 900 μM will not increase crop uptake and may contribute to inefficient N recovery by the crop. The existence of NH4−N and NO3−N simultaneously at the root surface may also lead to inefficient N recovery because of reduced uptake of NO3−N. 相似文献
7.
Piped streams, or streams that run underground, are often associated with urbanization. Despite the fact that they are ubiquitous in many urban watersheds, there is little empirical evidence regarding the ecological structure and function of piped stream reaches. This study measured ecosystem metabolism, nutrient uptake, and related characteristics of Pettee Brook—an urban stream that flows through several piped sections in Durham, New Hampshire, USA. Pettee Brook had high chloride and nutrient concentrations, low benthic biomass, and low rates of gross primary productivity (GPP), ecosystem respiration (ER), and nutrient uptake along its entire length during summer. Spring was a period of elevated biological activity, as increased light availability in the un-piped sections of the stream led to substantially higher GPP, ER, NH4 uptake, and PO4 uptake in these open reaches. Piped reaches of Pettee Brook were similar to open reaches in terms of water quality, dissolved O2 concentration, temperature, and discharge. Piped reaches did, however, have significantly less light, shallower sediments, and no debris dams. The absence of light inhibited autotrophic activity in piped reaches, resulting in the complete loss of GPP as well as a significant reduction in benthic AFDM and chlorophyll a biomass. Heterotrophic activity in piped reaches was not impaired to the same extent as autotrophic activity. Reduced ER was observed in piped reaches during the summer, but we failed to find significantly lower DOC or nutrient uptake rates in piped reaches than in open reaches. Carbon consumption in piped reaches, which do not have significant autochthonous or allochthonous carbon replenishment, must rely primarily on upstream inputs of organic matter. These results suggest that although ecological conditions in piped streams may be degraded beyond the extent of other urban stream reaches, piped reaches may still sustain some measurable ecosystem function. 相似文献
8.
Stream export of nitrogen (N) as nitrate (NO3−; the most mobile form of N) from forest ecosystems is thought to be controlled largely by plant uptake of inorganic N, such
that reduced demand for plant N during the non-growing season and following disturbances results in increased stream NO3− export. The roles of microbes and soils in ecosystem N retention are less clear, but are the dominant controls on N export
when plant uptake is low. We used a mass balance approach to investigate soil N retention during winter (December through
March) at the Hubbard Brook Experimental Forest by comparing NO3− inputs (atmospheric deposition), internal production (soil microbial nitrification), and stream output. We focused on months
when plant N uptake is nearly zero and the potential for N export is high. Although winter months accounted for only 10–15%
of annual net nitrification, soil NO3− production (0.8–1.0 g N m−2 winter−1) was much greater than stream export (0.03–0.19 N m−2 winter−1). Soil NO3− retention in two consecutive winters was high (96% of combined NO3− deposition and soil production; year 1) even following severe plant disturbance caused by an ice-storm (84%; year 2) We show
that soil NO3− retention is surprisingly high even when N demand by plants is low. Our study highlights the need to better understand mechanisms
of N retention during the non-growing season to predict how ecosystems will respond to high inputs of atmospheric N, disturbance,
and climate change. 相似文献
9.
Nitrification and Denitrification in Lake and Estuarine Sediments Measured by the 15N Dilution Technique and Isotope Pairing 总被引:1,自引:0,他引:1 下载免费PDF全文
Sren Rysgaard Nils Risgaard-Petersen Lars Peter Nielsen Niels Peter Revsbech 《Applied microbiology》1993,59(7):2093-2098
The transformation of nitrogen compounds in lake and estuarine sediments incubated in the dark was analyzed in a continuous-flowthrough system. The inflowing water contained 15NO3-, and by determination of the isotopic composition of the N2, NO3-, and NH4+ pools in the outflowing water, it was possible to quantify the following reactions: total NO3- uptake, denitrification based on NO3- from the overlying water, nitrification, coupled nitrification-denitrification, and N mineralization. In sediment cores from both lake and estuarine environments, benthic microphytes assimilated NO3- and NH4+ for a period of 25 to 60 h after darkening. Under steady-state conditions in the dark, denitrification of NO3- originating from the overlying water accounted for 91 to 171 μmol m-2 h-1 in the lake sediments and for 131 to 182 μmol m-2 h-1 in the estuarine sediments, corresponding to approximately 100% of the total NO3- uptake for both sediments. It seems that high NO3- uptake by benthic microphytes in the initial dark period may have been misinterpreted in earlier investigations as dissimilatory reduction to ammonium. The rates of coupled nitrification-denitrification within the sediments contributed to 10% of the total denitrification at steady state in the dark, and total nitrification was only twice as high as the coupled process. 相似文献
10.
Jirko Holst Chunyan Liu Nicolas Brüggemann Klaus Butterbach-Bahl Xunhua Zheng Yuesi Wang Shenghui Han Zhisheng Yao Jin Yue Xingguo Han 《Ecosystems》2007,10(4):623-634
Gross rates of N mineralization and nitrification, and soil–atmosphere fluxes of N2O, NO and NO2 were measured at differently grazed and ungrazed steppe grassland sites in the Xilin river catchment, Inner Mongolia, P. R.
China, during the 2004 and 2005 growing season. The experimental sites were a plot ungrazed since 1979 (UG79), a plot ungrazed
since 1999 (UG99), a plot moderately grazed in winter (WG), and an overgrazed plot (OG), all in close vicinity to each other.
Gross rates of N mineralization and nitrification determined at in situ soil moisture and soil temperature conditions were
in a range of 0.5–4.1 mg N kg−1 soil dry weight day−1. In 2005, gross N turnover rates were significantly higher at the UG79 plot than at the UG99 plot, which in turn had significantly
higher gross N turnover rates than the WG and OG plots. The WG and the OG plot were not significantly different in gross ammonification
and in gross nitrification rates. Site differences in SOC content, bulk density and texture could explain only less than 15%
of the observed site differences in gross N turnover rates. N2O and NO
x
flux rates were very low during both growing seasons. No significant differences in N trace gas fluxes were found between
plots. Mean values of N2O fluxes varied between 0.39 and 1.60 μg N2O-N m−2 h−1, equivalent to 0.03–0.14 kg N2O-N ha−1 y−1, and were considerably lower than previously reported for the same region. NO
x
flux rates ranged between 0.16 and 0.48 μg NO
x
-N m−2 h−1, equivalent to 0.01–0.04 kg NO
x
-N ha−1 y−1, respectively. N2O fluxes were significantly correlated with soil temperature and soil moisture. The correlations, however, explained only
less than 20% of the flux variance. 相似文献
11.
During summer and autumn 1988, benthic fluxes of nutrients and oxygen were measured in the Bay of Cadiz. The study was carried
out using benthic chambers and in addition by determining gradients of nutrient concentration in interstitial water. Fluxes
ranged between 13.5–24.3, 3.4–7.8, 6.1–28.4 and (− 99.4)−(− 188.5) mmol m− 2 d−1 for NH4
+ , o-P, SiO2 and O2 respectively. These values are far higher than those reported by other authors for locations at similar latitudes. The stoichiometry
of O, N and P transference suggest that benthic degradation of principally allochthonous organic matter takes place mainly
through anaerobic pathways. 相似文献
12.
Headwater streams are key sites of nutrient and organic matter processing and retention, but little is known about temporal
variability in gross primary production (GPP) and ecosystem respiration (ER) rates as a result of the short duration of most
metabolism measurements in lotic ecosystems. We examined temporal variability and controls on ecosystem metabolism by measuring
daily rates continuously for 2 years in Walker Branch, a first-order deciduous forest stream. Four important scales of temporal
variability in ecosystem metabolism rates were identified: (1) seasonal, (2) day-to-day, (3) episodic (storm-related), and
(4) inter-annual. Seasonal patterns were largely controlled by the leaf phenology and productivity of the deciduous riparian
forest. Walker Branch was strongly net heterotrophic throughout the year with the exception of the open-canopy spring when
GPP and ER rates were co-equal. Day-to-day variability in weather conditions influenced light reaching the streambed, resulting
in high day-to-day variability in GPP particularly during spring (daily light levels explained 84% of the variance in daily
GPP in April). Episodic storms depressed GPP for several days in spring, but increased GPP in autumn by removing leaves shading
the streambed. Storms depressed ER initially, but then stimulated ER to 2–3 times pre-storm levels for several days. Walker
Branch was strongly net heterotrophic in both years of the study, with annual GPP being similar (488 and 519 g O2 m−2 y−1 or 183 and 195 g C m−2 y−1) but annual ER being higher in 2004 than 2005 (−1,645 vs. −1,292 g O2 m−2 y−1 or −617 and −485 g C m−2 y−1). Inter-annual variability in ecosystem metabolism (assessed by comparing 2004 and 2005 rates with previous measurements)
was the result of the storm frequency and timing and the size of the spring macroalgal bloom. Changes in local climate can
have substantial impacts on stream ecosystem metabolism rates and ultimately influence the carbon source and sink properties
of these important ecosystems. 相似文献
13.
Rafiqa Améziane Céline Richard-Molard Eliane Deléens Jean-François Morot-Gaudry Anis M. Limami 《Planta》1997,202(3):303-312
In chicory, we examined how NO3
− supply affected NO3
− uptake, N partitioning between shoot and root and N accumulation in the tuberized root throughout the vegetative period.
Plants were grown at two NO3
− concentrations: 0.6 and 3 mM. We used 15N-labelling/chase experiments for the quantification of N fluxes between shoot and root and for determining whether N stored
in the tuberized root originates from N remobilized from the shoot or from recently absorbed NO3
−. The rate of 15NO3
− uptake was decreased by low NO3
− availability at all stages of growth. In young plants (10–55 days after sowing; DAS), in both NO3
− treatments the leaves were the strongest sink for 15N. In mature (tuberizing) plants, (55–115 DAS), the rate of 15NO3
− uptake increased as well as the amount of exogenous N allocated to the root. In N-limited plants, N allocation to the tuberized
root relied essentially on recent N absorption, while in N-replete plants, N remobilized from the shoot contributed more to
N-reserve accumulation in the root. In senescing plants (115–170 DAS) the rate of 15NO3
− uptake decreased mainly in N-replete plants whereas it remained almost unchanged in N-limited plants. In both NO3
− treatments the tuberized root was the strongest sink for recently absorbed N. Remobilization of previously absorbed N from
shoot to tuberized root increased greatly in N-limited plants, whereas it increased slightly in N-replete plants. As a consequence,
accumulation of the N-storage compounds vegetative storage protein (VSP) and arginine was delayed until later in the vegetative
period in N-limited plants. Our results show that although the dynamics of N storage was affected by NO3
− supply, the final content of total N, VSP and arginine in roots was almost the same in N-limited and N-replete plants. This
indicates that chicory is able to build up a store of available N-reserves, even when plants are grown on low N. We also suggest
that in tuberized roots there is a maximal capacity for N accumulation, which was reached earlier (soon after 100 DAS) in
N-replete plants. This hypothesis is supported by the fact that in N-replete plants despite NO3
− availability, N accumulation ceased and significant amounts of N were lost due to N efflux.
Received: 14 October 1996 / Accepted: 4 February 1997 相似文献
14.
Site-dependent N uptake from N-form mixtures by arctic plants,soil microbes and ectomycorrhizal fungi 总被引:1,自引:0,他引:1
Soil microbes constitute an important control on nitrogen (N) turnover and retention in arctic ecosystems where N availability
is the main constraint on primary production. Ectomycorrhizal (ECM) symbioses may facilitate plant competition for the specific
N pools available in various arctic ecosystems. We report here our study on the N uptake patterns of coexisting plants and
microbes at two tundra sites with contrasting dominance of the circumpolar ECM shrub Betula nana. We added equimolar mixtures of glycine-N, NH4+–N and NO3−–N, with one N form labelled with 15N at a time, and in the case of glycine, also labelled with 13C, either directly to the soil or to ECM fungal ingrowth bags. After 2 days, the vegetation contained 5.6, 7.7 and 9.1% (heath
tundra) and 7.1, 14.3 and 12.5% (shrub tundra) of the glycine-, NH4+- and NO3−–15N, respectively, recovered in the plant–soil system, and the major part of 15N in the soil was immobilized by microbes (chloroform fumigation-extraction). In the subsequent 24 days, microbial N turnover
transferred about half of the immobilized 15N to the non-extractable soil organic N pool, demonstrating that soil microbes played a major role in N turnover and retention
in both tundra types. The ECM mycelial communities at the two tundras differed in N-form preferences, with a higher contribution
of glycine to total N uptake at the heath tundra; however, the ECM mycelial communities at both sites strongly discriminated
against NO3−. Betula nana did not directly reflect ECM mycelial N uptake, and we conclude that N uptake by ECM plants is modulated by the N uptake
patterns of both fungal and plant components of the symbiosis and by competitive interactions in the soil. Our field study
furthermore showed that intact free amino acids are potentially important N sources for arctic ECM fungi and plants as well
as for soil microorganisms.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
15.
Jonathan M. O’Brien Walter K. Dodds Kymberly C. Wilson Justin N. Murdock Jessica Eichmiller 《Biogeochemistry》2007,84(1):31-49
We conducted 15NO3− stable isotope tracer releases in nine streams with varied intensities and types of human impacts in the upstream watershed
to measure nitrate (NO3−) cycling dynamics. Mean ambient NO3− concentrations of the streams ranged from 0.9 to 21,000 μg l−1 NO3−–N. Major N-transforming processes, including uptake, nitrification, and denitrification, all increased approximately two
to three orders of magnitude along the same gradient. Despite increases in transformation rates, the efficiency with which
stream biota utilized available NO3−-decreased along the gradient of increasing NO3−. Observed functional relationships of biological N transformations (uptake and nitrification) with NO3− concentration did not support a 1st order model and did not show signs of Michaelis–Menten type saturation. The empirical
relationship was best described by a Efficiency Loss model, in which log-transformed rates (uptake and nitrification) increase
with log-transformed nitrate concentration with a slope less than one. Denitrification increased linearly across the gradient
of NO3− concentrations, but only accounted for ∼1% of total NO3− uptake. On average, 20% of stream water NO3− was lost to denitrification per km, but the percentage removed in most streams was <5% km−1. Although the rate of cycling was greater in streams with larger NO3− concentrations, the relative proportion of NO3− retained per unit length of stream decreased as NO3− concentration increased. Due to the rapid rate of NO3− turnover, these streams have a great potential for short-term retention of N from the landscape, but the ability to remove
N through denitrification is highly variable. 相似文献
16.
17.
Late-successional forests in the upper Great Lakes region are susceptible to nitrogen (N) saturation and subsequent nitrate
(NO3−) leaching loss. Endemic wind disturbances (i.e., treefall gaps) alter tree uptake and soil N dynamics; and, gaps are particular
susceptible to NO3− leaching loss. Inorganic N was measured throughout two snow-free periods in throughfall, forest floor leachates, and mineral
soil leachates in gaps (300–2,000 m2, 6–9 years old), gap-edges, and closed forest plots in late-successional northern hardwood, hemlock, and northern hardwood–hemlock
stands. Differences in forest water inorganic N among gaps, edges, and closed forest plots were consistent across these cover
types: NO3− inputs in throughfall were significantly greater in undisturbed forest plots compared with gaps and edges; forest floor leachate
NO3− was significantly greater in gaps compared to edges and closed forest plots; and soil leachate NO3− was significantly greater in gaps compared to the closed forest. Significant differences in forest water ammonium and pH
were not detected. Compared to suspected N-saturated forests with high soil NO3− leaching, undisturbed forest plots in these late-successional forests are not losing NO3− (net annual gain of 2.8 kg ha−1) and are likely not N-saturated. Net annual NO3− losses were observed in gaps (1.3 kg ha−1) and gap-edges (0.2 kg ha−1), but we suspect these N leaching losses are a result of decreased plant uptake and increased soil N mineralization associated
with disturbance, and not N-saturation. 相似文献
18.
Estimating the uptake of traffic-derived NO2 from 15N abundance in Norway spruce needles 总被引:1,自引:0,他引:1
The 15N ratio of nitrogen oxides (NOx) emitted from vehicles, measured in the air adjacent to a highway in the Swiss Middle Land, was very high [δ15N(NO2) = +5.7‰]. This high 15N abundance was used to estimate long-term NO2 dry deposition into a forest ecosystem by measuring δ15N in the needles and the soil of potted and autochthonous spruce trees [Picea abies (L.) Karst] exposed to NO2 in a transect orthogonal to the highway. δ15N in the current-year needles of potted trees was 2.0‰ higher than that of the control after 4 months of exposure close to
the highway, suggesting a 25% contribution to the N-nutrition of these needles. Needle fall into the pots was prevented by
grids placed above the soil, while the continuous decomposition of needle litter below the autochthonous trees over previous
years has increased δ15N values in the soil, resulting in parallel gradients of δ15N in soil and needles with distance from the highway. Estimates of NO2 uptake into needles obtained from the δ15N data were significantly correlated with the inputs calculated with a shoot gas exchange model based on a parameterisation
widely used in deposition modelling. Therefore, we provide an indication of estimated N inputs to forest ecosystems via dry
deposition of NO2 at the receptor level under field conditions.
Received: 7 November 1997 / Accepted: 16 September 1998 相似文献
19.
Oxygen and CO2 fluxes were measured in hydroponically grown mycorrhizal and non-mycorrhizal Triticum aestivum L. cv. Hano roots. The NO3
– uptake of the plants was used to estimate the amount of root respiration attributable to ion uptake. Plants were grown at
4 mM N and 10 μM P, where a total and viable mycorrhizal root colonisation of 48% and 18%, respectively, by Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) was observed. The O2 consumption and NO3
– uptake rates were similar and the CO2 release was higher in mycorrhizal than in non-mycorrhizal wheat. This resulted in a significantly higher respiratory quotient
(RQ, mol CO2 mol–1 O2) in mycorrhizal (1.27±0.13) than in non-mycorrhizal (0.79±0.05) wheat. As the biomass and N and P concentrations in mycorrhizal
and non-mycorrhizal wheat were the same, the higher RQ resulted from the mycorrhizal colonisation and not differences in nutrition
per se.
Accepted: 26 March 1999 相似文献
20.
Emission and plant uptake of atmospheric nitrogen oxides (NO + NO2) significantly influence regional climate change by regulating the oxidative chemistry of the lower atmosphere, species composition
and the recycling of carbon and nutrients, etc. Plant uptake of nitrogen dioxide (NO2) is concentration-dependent and species-specific, and covaries with environmental factors. An important factor determining
NO2 influx into leaves is the replenishment of the substomatal cavity. The apoplastic chemistry of the substomatal cavity plays
crucial roles in NO2 deposition rates and the tolerance to NO2, involving the reactions between NO2 and apoplastic antioxidants, NO2-responsive germin-like proteins, apoplastic acidification, and nitrite-dependent NO synthesis, etc. Moreover, leaf apoplast
is a favorable site for the colonization by microbes, which disturbs nitrogen metabolism of host plants. For most plant species,
NO2 assimilation in a leaf primarily depends on the nitrate (NO3
−) assimilation pathway. NO2–N assimilation is coupled with carbon and sulfur (sulfate and SO2) assimilation as indicated by the mutual needs for metabolic intermediates (or metabolites) and the NO2-caused changes of key metabolic enzymes such as phosphoenolpyruvate carboxylase (PEPc) and adenosine 5′-phosphosulfate sulfotransferase,
organic acids, and photorespiration. Moreover, arbuscular mycorrhizal (AM) colonization improves the tolerance of host plants
to NO2 by enhancing the efficiency of nutrient absorption and translocation and influencing foliar chemistry. Further progress is
proposed to gain a better understanding of the coordination between NO2–N, S and C assimilation, especially the investigation of metabolic checkpoints, and the effects of photorespiratory nitrogen
cycle, diverse PEPc and the metabolites such as cysteine, O-acetylserine (OAS) and glutathione. 相似文献