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1.
The ability of an ecosystem to retain anthropogenic nitrogen (N) deposition is dependent upon plant and soil sinks for N,
the strengths of which may be altered by chronic atmospheric N deposition. Sugar maple (Acer saccharum Marsh.), the dominant overstory tree in northern hardwood forests of the Lake States region, has a limited capacity to take
up and assimilate NO3−. However, it is uncertain whether long-term exposure to NO3− deposition might induce NO3− uptake by this ecologically important overstory tree. Here, we investigate whether 10 years of experimental NO3− deposition (30 kg N ha−1 y−1) could induce NO3− uptake and assimilation in overstory sugar maple (approximately 90 years old), which would enable this species to function
as a direct sink for atmospheric NO3− deposition. Kinetic parameters for NH4+ and NO3− uptake in fine roots, as well as leaf and root NO3− reductase activity, were measured under conditions of ambient and experimental NO3− deposition in four sugar maple-dominated stands spanning the geographic distribution of northern hardwood forests in the
Upper Lake States. Chronic NO3− deposition did not alter the V
max or K
m for NO3− and NH4+ uptake nor did it influence NO3− reductase activity in leaves and fine roots. Moreover, the mean V
max for NH4+ uptake (5.15 μmol 15N g−1 h−1) was eight times greater than the V
max for NO3− uptake (0.63 μmol 15N g−1 h−1), indicating a much greater physiological capacity for NH4+ uptake in this species. Additionally, NO3− reductase activity was lower than most values for woody plants previously reported in the literature, further indicating
a low physiological potential for NO3− assimilation in sugar maple. Our results demonstrate that chronic NO3− deposition has not induced the physiological capacity for NO3− uptake and assimilation by sugar maple, making this dominant species an unlikely direct sink for anthropogenic NO3− deposition. 相似文献
2.
The kinetics of NH4
+ and NO3
− uptake in young Douglas fir trees (Pseudotsuga menziesii [Mirb.] Franco) were studied in solutions, containing either one or both N species. Using solutions containing a single N
species, the Vmax of NH4
+ uptake was higher than that of NO3
− uptake. The Km of NH4
+ uptake and Km of NO3
− uptake differed not significantly. When both NH4
+ and NO3
− were present, the Vmax for NH4
+ uptake became slightly higher, and the Km for NH4
+ uptake remained in the same order. Under these conditions the NO3
− uptake was almost totally inhibited over the whole range of concentrations used (10–1000 μM total N). This inhibition by NH4
+ occurred during the first two hours after addition. ei]{gnA C}{fnBorstlap} 相似文献
3.
Eva Ritter 《Plant and Soil》2007,295(1-2):239-251
Afforestation has become an important tool for soil protection and land reclamation in Iceland. Nevertheless, the harsh climate
and degraded soils are growth-limiting for trees, and little is know about changes in soil nutrients in maturing forests planted
on the volcanic soils. In the present chronosequence study, changes in C, N and total P in soil (0–10 and 10–20 cm depth)
and C and N in foliar tissue were investigated in stands of native Downy birch (Betula pubescens Enrh.) and the in Iceland introduced Siberian larch (Larix sibirica Ledeb.). The forest stands were between 14 and 97 years old and were established on heath land that had been treeless for
centuries. Soils were Andosols derived from basaltic material and rhyolitic volcanic ash. A significant effect of tree species
was only found for the N content in foliar tissue. Foliar N concentrations were significantly higher and foliar C/N ratios
significantly lower in larch needles than in birch leaves. There was no effect of stand age. Changes in soil C and the soil
nutrient status with time after afforestation were little significant. Soil C concentrations in 0–10 cm depth in forest stands
older than 30 years were significantly higher than in heath land and forest stands younger than 30 years. This was attributed
to a slow accumulation of organic matter. Soil N concentrations and soil Ptot were not affected by stand age. Nutrient pools in the two soil layers were calculated for an average weight of soil material
(400 Mg soil ha−1 in 0–10 cm depth and 600 Mg soil ha−1 in 10–20 cm depth, respectively). Soil nutrient pools did not change significantly with time. Soil C pools were in average
23.6 Mg ha−1 in the upper soil layer and 16.9 Mg ha−1 in the lower soil layer. The highest annual increase in soil C under forest compared to heath land was 0.23 Mg C ha−1 year−1 in 0–10 cm depth calculated for the 53-year-old larch stand. Soil N pools were in average 1.0 Mg N ha−1 in both soil layers and did not decrease with time despite a low N deposition and the uptake and accumulation of N in biomass
of the growing trees. Soil Ptot pools were in average 220 and 320 kg P ha−1 in the upper and lower soil layer, respectively. It was assumed that mycorrhizal fungi present in the stands had an influence
on the availability of N and P to the trees.
Responsible Editor: Hans Lambers. 相似文献
4.
Plant and microbial nitrogen use and turnover: Rapid conversion of nitrate to ammonium in soil with roots 总被引:2,自引:0,他引:2
Immobilization of ammonium (NH
4
+
) by plants and microbes, a controlling factor of ecosystem nitrogen (N) retention, has usually been measured based on uptake
of15NH
4
+
solutions injected into soil. To study the influence of roots on N dynamics without stimulating consumption of NH
4
+
, we estimated gross nitrification in the presence or absence of live roots in an agricultural soil. Tomato (Lycopersicon esculentum var. Peto76) plants were grown in microcosms containing root exclosures. When the plants were 7 weeks old,15N enriched nitrate (NO
3
−
) was applied in the 0–150 mm soil layer. After 24 h, > 30 times more15NH
4
+
was found in the soil with roots than in the soil of the root exclosures. At least 18% of the NH
4
+
-N present at this time in the soil with roots had been converted from NO
3
−
. We estimated rates of conversion of NO
3
−
to NH
4
+
, and rates ofNH
4
+
immobilization by plants and microbes, by simulating N-flow of14+15N and15N in three models representing mechanisms that may be underlying the experimental data: Dissimilatory NO
3
−
reduction to NH
4
+
(DNRA), plant N efflux, and microbial biomass nitrogen (MBN) turnover. Compared to NO
3
−
uptake, plant NH
4
+
uptake was modest. Ammonium immobilization by plants and microbes was equal to at least 35% of nitrification rates. The rapid
recycling of NO
3
−
to NH
4
+
via plants and/or microbes contributes to ecosystem N retention and may enable plants growing in agricultural soils to capture
more NH
4
+
than generally assumed. 相似文献
5.
T. Rütting D. Huygens C. Müller O. Van Cleemput R. Godoy P. Boeckx 《Biogeochemistry》2008,90(3):243-258
Nitrite (NO2
−) is an intermediate in a variety of soil N cycling processes. However, NO2
− dynamics are often not included in studies that explore the N cycle in soil. Within the presented study, nitrite dynamics
were investigated in a Nothofagus betuloides forest on an Andisol in southern Chile. We carried out a 15N tracing study with six 15N labeling treatments, including combinations of NO3
−, NH4
+ and NO2
−. Gross N transformation rates were quantified with a 15N tracing model in combination with a Markov chain Monte Carlo optimization routine. Our results indicate the occurrence of
functional links between (1) NH4
+ oxidation, the main process for NO2
− production (nitritation), and NO2
− reduction, and (2) oxidation of soil organic N, the dominant NO3
− production process in this soil, and dissimilatory NO3
− reduction to NH4
+ (DNRA). The production of NH4
+ via DNRA was approximately ten times higher than direct mineralization from recalcitrant soil organic matter. Moreover, the
rate of DNRA was several magnitudes higher than the rate of other NO3
− reducing processes, indicating that DNRA is able to outcompete denitrification, which is most likely not an important process
in this ecosystem. These functional links are most likely adaptations of the microbial community to the prevailing pedo-climatic
conditions of this Nothofagus ecosystem. 相似文献
6.
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
7.
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
8.
Intact amino acid uptake by northern hardwood and conifer trees 总被引:1,自引:0,他引:1
Anne Gallet-Budynek Edward Brzostek Vikki L. Rodgers Jennifer M. Talbot Sharon Hyzy Adrien C. Finzi 《Oecologia》2009,160(1):129-138
Empirical and modeling studies of the N cycle in temperate forests of eastern North America have focused on the mechanisms
regulating the production of inorganic N, and assumed that only inorganic forms of N are available for plant growth. Recent
isotope studies in field conditions suggest that amino acid capture is a widespread ecological phenomenon, although northern
temperate forests have yet to be studied. We quantified fine root biomass and applied tracer-level quantities of U–13C2–15N-glycine, 15NH4
+ and 15NO3
− in two stands, one dominated by sugar maple and white ash, the other dominated by red oak, beech, and hemlock, to assess
the importance of amino acids to the N nutrition of northeastern US forests. Significant enrichment of 13C in fine roots 2 and 5 h following tracer application indicated intact glycine uptake in both stands. Glycine accounted for
up to 77% of total N uptake in the oak–beech–hemlock stand, a stand that produces recalcitrant litter, cycles N slowly and
has a thick, amino acid-rich organic horizon. By contrast, glycine accounted for only 20% of total N uptake in the sugar maple
and white ash stand, a stand characterized by labile litter and rapid rates of amino acid production and turnover resulting
in high rates of mineralization and nitrification. This study shows that amino acid uptake is an important process occurring
in two widespread, northeastern US temperate forest types with widely differing rates of N cycling. 相似文献
9.
Isotopic signature of nitrate in two contrasting watersheds of Brush Brook,Vermont, USA 总被引:2,自引:0,他引:2
We used the dual isotope method to study differences in nitrate export in two subwatersheds in Vermont, USA. Precipitation,
soil water and streamwater samples were collected from two watersheds in Camels Hump State Forest, located within the Green
Mountains of Vermont. These samples were analyzed for the δ15N and δ18O of NO3−. The range of δ15N–NO3− values overlapped, with precipitation −4.5‰ to +2.0‰ (n = 14), soil solution −10.3‰ to +6.2‰ (n = 12) and streamwater +0.3‰ to +3.1‰ (n = 69). The δ18O of precipitation NO3− (mean 46.8 ± 11.5‰) was significantly different (P < 0.001) from that of the stream (mean 13.2 ± 4.3‰) and soil waters (mean 14.5 ± 4.2‰) even during snowmelt periods. Extracted
soil solution and streamwater δ18O of NO3− were similar and within the established range of microbially produced NO3−, demonstrating that NO3− was formed by microbial processes. The δ15N and δ18O of NO3− suggests that although the two tributaries have different seasonal NO3− concentrations, they have a similar NO3− source. 相似文献
10.
Donald R. Zak William E. Holmes Matthew J. Tomlinson Kurt S. Pregitzer Andrew J. Burton 《Ecosystems》2006,9(2):242-253
Sugar maple (Acer saccharum Marsh.)-dominated northern hardwood forests in the upper Lakes States region appear to be particularly sensitive to chronic
atmospheric NO3− deposition. Experimental NO3− deposition (3 g NO3− N m−2 y−1) has significantly reduced soil respiration and increased the export of DOC/DON and NO3− across the region. Here, we evaluate the possibility that diminished microbial activity in mineral soil was responsible for
these ecosystem-level responses to NO3− deposition. To test this alternative, we measured microbial biomass, respiration, and N transformations in the mineral soil
of four northern hardwood stands that have received 9 years of experimental NO3− deposition. Microbial biomass, microbial respiration, and daily rates of gross and net N transformations were not changed
by NO3− deposition. We also observed no effect of NO3− deposition on annual rates of net N mineralization. However, NO3− deposition significantly increased (27%) annual net nitrification, a response that resulted from rapid microbial NO3− assimilation, the subsequent turnover of NH4+, and increased substrate availability for this process. Nonetheless, greater rates of net nitrification were insufficient
to produce the 10-fold observed increase in NO3− export, suggesting that much of the exported NO3− resulted directly from the NO3− deposition treatment. Results suggest that declines in soil respiration and increases in DOC/DON export cannot be attributed
to NO3−-induced physiological changes in mineral soil microbial activity. Given the lack of response we have observed in mineral
soil, our results point to the potential importance of microbial communities in forest floor, including both saprotrophs and
mycorrhizae, in mediating ecosystem-level responses to chronic NO3− deposition in Lake States northern hardwood forests. 相似文献
11.
Massive anthropogenic acceleration of the global nitrogen (N) cycle has stimulated interest in understanding the fate of excess
N loading to aquatic ecosystems. Nitrate (NO3
−) is traditionally thought to be removed mainly by microbial respiratory denitrification coupled to carbon (C) oxidation,
or through biomass assimilation. Alternatively, chemolithoautotrophic bacterial metabolism may remove NO3
− by coupling its reduction with the oxidation of sulfide to sulfate (SO4
2−). The NO3
− may be reduced to N2 or to NH4
+, a form of dissimilatory nitrate reduction to ammonium (DNRA). The objectives of this study were to investigate the importance
of S oxidation as a NO3
− removal process across diverse freshwater streams, lakes, and wetlands in southwestern Michigan (USA). Simultaneous NO3
− removal and SO4
2− production were observed in situ using modified “push-pull” methods in nine streams, nine wetlands, and three lakes. The
measured SO4
2− production can account for a significant fraction (25–40%) of the overall NO3
− removal. Addition of 15NO3
− and measurement of 15NH4
+ production using the push–pull method revealed that DNRA was a potentially important process of NO3
− removal, particularly in wetland sediments. Enrichment cultures suggest that Thiomicrospira denitrificans may be one of the organisms responsible for this metabolism. These results indicate that NO3
−-driven SO4
2− production could be widespread and biogeochemically important in freshwater sediments. Removal of NO3
− by DNRA may not ameliorate problems such as eutrophication because the N remains bio-available. Additionally, if sulfur (S)
pollution enhances NO3
− removal in freshwaters, then controls on N processing in landscapes subject to S and N pollution are more complex than previously
appreciated.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
12.
15N labelled (NH4)2SO4 was applied to barley at 5 g N m−2 (50 kg N ha−1) in microplots at sowing to study the timing of the N losses and the contribution of soil and fertilizer N to the plant.
Water treatments included rainfed and irrigation at 45–50 mm deficit beginning in the spring.
Recovery of15N in the plant increased to a maximum of about 20% within 91 days after sowing (DAS 91) and then remained constant. Approximately
16% (0.8 g N m−2) of the fertilizer was in the stem and leaves at DAS 91 and this N was subsequently redistributed to the head. At maturity,
approximately 75% of the15N assimilated by the tops was recovered in the grain. Soil N contributed 3.6 g N m−2 to the head; 2.2 g N m−2 was remobilized from the stem and leaves, and the balance, approximately 1.4 g N m−2, was taken up from the soil between DAS 69 to 91. Effects of irrigation treatments on N accumulation were not significant.
Residual15N fertilizer in the soil decreased with time from sowing, and at maturity 40% of the applied N was recovered in the surface
0.15 m.15N movement to depth was limited and less than 5% of the fertilizer was recovered below 0.15 m. Irrigation had no effect on
the15N recovery at depth.
Total recovery of the15N varied between 60 and 67% and implies that 33–40% was lost from the soil-plant system. The total recovery in the soil and
plant was not affected by time or irrigation in the interval DAS 39 to 134. Losses occurred before DAS 39 when crop uptake
of N was small and soil mineral N content was high. There was an apparent loss of 1.9 g fertilizer N m−2 (i.e. 38% of that applied) between DAS 1 and 15. This loss occurred before crop emergence when rainfall provided conditions suitable
for denitrification. 相似文献
13.
Carbon isotopic composition of soils subjected to C3–C4 vegetation change can be used to estimate C turnover in bulk soil and in soil organic matter (SOM) pools with fast and intermediate
turnover rates. We hypothesized that the biological availability of SOM pools is inversely proportional to their thermal stability,
so that thermogravimetry can be used to separate SOM pools with contrasting turnover rates. Soil samples from a field plot
cultivated for 10.5 years with the perennial C4 plant Miscanthus×gigantheus were analyzed by thermogravimetry coupled with differential scanning calorimetry (DSC). Three SOM fractions were distinguished
according to the differential weight losses and exothermic or endothermic reactions measured by DSC. The δ13C and δ15N values of these three fractions obtained by gradual soil heating were measured by IRMS. The weight losses up to 190 °C mainly
reflected water evaporation because no significant C and N losses were detected and δ13C and δ15N values of the residual SOM remained unchanged. The δ13C values (−16.4‰) of SOM fraction decomposed between 190 and 390 °C (containing 79% of total soil C) were slightly closer
to that of the Miscanthus plant tissues (δ13C = −11.8‰) compared to the δ13C values (−16.8‰) of SOM fraction decomposed above 390 °C containing the residual 21% of SOM. Thus, the C turnover in the
thermally labile fraction was faster than that in thermally stable fractions, but the differences were not very strong. Therefore,
in this first study combining TG-DSC with isotopic analysis, we conclude that the thermal stability of SOM was not very strongly
related to biological availability of SOM fractions. In contrast to δ13C, the δ15N values strongly differed between SOM fractions, suggesting that N turnover in the soil was different from C turnover. More
detailed fractionation of SOM by thermal analysis with subsequent isotopic analysis may improve the resolution for δ13C. 相似文献
14.
Plant and Soil N Response of Southern Californian Semi-arid Shrublands After 1 Year of Experimental N Deposition 总被引:1,自引:0,他引:1
Large inputs of atmospheric N from dry deposition accumulate on vegetation and soil surfaces of southern Californian chaparral
and coastal sage scrub (CSS) ecosystems during the late-summer and early-fall and become available as a pulse following winter
rainfall; however, the fate of this dry season atmospheric N addition is unknown. To assess the potential for dry season atmospheric
N inputs to be incorporated into soil and/or vegetation N pools, an in situ N addition experiment was initiated in a post-fire
chaparral and a mature CSS stand where 10 × 10 m plots were exposed to either ambient N deposition (control) or ambient +50 kg
N ha−1 (added N) added as NH4NO3 during a single application in October 2003. After 1 year of N addition, plots exposed to added N had significantly higher
accumulation of extractable inorganic N (NH4−N + NO3−N) on ion exchange resins deployed in the 0–10 cm mineral soil layer and higher soil extractable N in the subsurface (30–40 cm)
mineral soil than plots exposed to ambient N. Chaparral and CSS shrubs exposed to added N also exhibited a significant increase
in tissue N concentration and a decline in the tissue C:N ratio, and added N significantly altered the shrub tissue δ
15N natural abundance. Leaching of inorganic N to 1 m below the soil surface was on average 2–3 times higher in the added N
plots, but large within treatment variability cause these differences to be statistically insignificant. Although a large
fraction of the added N could not be accounted for in the shrub and soil N pools investigated, these observations suggest
that dry season N inputs can significantly and rapidly alter N availability and shrub tissue chemistry in Mediterranean-type
chaparral and CSS shrublands of southern California. 相似文献
15.
Katja Pörtl Sophie Zechmeister-Boltenstern Wolfgang Wanek Per Ambus Torsten W. Berger 《Plant and Soil》2007,295(1-2):79-94
Natural 15N abundance measurements of ecosystem nitrogen (N) pools and 15N pool dilution assays of gross N transformation rates were applied to investigate the potential of δ15N signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure
spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil δ15N values of both forest sites increased with depth to 50 cm, but then decreased below this zone. δ15N values of microbial biomass (mixed stand: 4.7 ± 0.8‰, spruce stand: 5.9 ± 0.9‰) and of dissolved organic N (DON; mixed stand:
5.3 ± 1.7‰, spruce stand: 2.6 ± 3.3‰) were not significantly different; these pools were most enriched in 15N of all soil N pools. Denitrification represented the main N2O-producing process in the mixed forest stand as we detected a significant 15N enrichment of its substrate NO3− (3.6 ± 4.5‰) compared to NH4+ (−4.6 ± 2.6‰) and its product N2O (−11.8 ± 3.2‰). In a 15N-labelling experiment in the spruce stand, nitrification contributed more to N2O production than denitrification. Moreover, in natural abundance measurements the NH4+ pool was slightly 15N-enriched (−0.4 ± 2.0 ‰) compared to NO3− (−3.0 ± 0.6 ‰) and N2O (−2.1 ± 1.1 ‰) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N2O. The more positive δ15N values of N2O in the spruce stand than in the mixed stand point to extensive microbial N2O reduction in the spruce stand. Combining natural 15N abundance and 15N tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately. 相似文献
16.
Patricia Torres-Cañabate Eric A. Davidson Ekaterina Bulygina Roberto García-Ruiz Jose A. Carreira 《Biogeochemistry》2008,91(1):1-11
Evidence for abiotic immobilization of nitrogen (N) in soil is accumulating, but remains controversial. Identifying the fate
of N from atmospheric deposition is important for understanding the N cycle of forest ecosystems. We studied soils of two
Abies pinsapo fir forests under Mediterranean climate seasonality in southern Spain—one with low N availability and the other with symptoms
of N saturation. We hypothesized that biotic and abiotic immobilization of nitrate (NO3
−) would be lower in soils under these forests compared to more mesic temperate forests, and that the N saturated stand would
have the lowest rates of NO3
− immobilization. Live and autoclaved soils were incubated with added 15NO3
− (10 μg N g−1 dry soil; 99% enriched) for 24 h, and the label was recovered as total dissolved-N, NO3
−, ammonium (NH4
+), or dissolved organic-N (DON). To evaluate concerns about possible iron interference in analysis of NO3
− concentrations, both flow injection analysis (FIA) and ion chromatography (IC) were applied to water extracts, soluble iron
was measured in both water and salt extracts, and standard additions of NO3
− to salt extracts were analyzed. Good agreement between FIA and IC analysis, low concentrations of soluble Fe, and 100% (±3%)
recovery of NO3
− standard additions all pointed to absence of an interference problem for NO3
− quantification. On average, 85% of the added 15NO3
− label was recovered as 15NO3
−, which supports our hypothesis that rates of immobilization were generally low in these soils. A small amount (mean = 0.06 μg N g−1 dry soil) was recovered as 15NH4
+ in live soils and none in sterilized soils. Mean recovery as DO15N ranged from 0.6 to 1.5 μg N g−1 dry soil, with no statistically significant effect of sterilization or soil type, indicating that this was an abiotic process
that occurred at similar rates in both soils. These results demonstrate a detectable, but modest rate of abiotic immobilization
of NO3
− to DON, supporting our first hypothesis. These mineral soils may not have adequate carbon availability to support the regeneration
of reducing microsites needed for high rates of NO3
− reduction. Our second hypothesis regarding lower expected abiotic immobilization in soils from the N-saturated site was not
supported. The rates of N deposition in this region may not be high enough to have swamped the capacity for soil NO3
− immobilization, even in the stand showing some symptoms of N saturation. A growing body of evidence suggests that soil abiotic
NO3
− immobilization is common, but that rates are influenced by a combination of factors, including the presence of plentiful
available carbon, reduced minerals in anaerobic microsites and adequate NO3
− supply. 相似文献
17.
In this study we show that the natural abundance of the nitrogen isotope 15, δ15N, of plants in heath tundra and at the tundra-forest ecocline is closely correlated with the presence and type of mycorrhizal
association in the plant roots. A total of 56 vascular plant species, 7 moss species, 2 lichens and 6 species of fungi from
four heath and forest tundra sites in Greenland, Siberia and Sweden were analysed for δ15N and N concentration. Roots of vascular plants were examined for mycorrhizal colonization, and the soil organic matter was
analysed for δ15N, N concentration and soil inorganic, dissolved organic and microbial N. No arbuscular mycorrhizal (AM) colonizations were
found although potential host plants were present in all sites. The dominant species were either ectomycorrhizal (ECM) or
ericoid mycorrhizal (ERI). The δ15N of ECM or ERI plants was 3.5–7.7‰ lower than that of non-mycorrhizal (NON) species in three of the four sites. This corresponds
to the results in our earlier study of mycorrhiza and plant δ15N which was limited to one heath and one fellfield in N Sweden. Hence, our data suggest that the δ15N pattern: NON/AM plants > ECM plants ≥ ERI plants is a general phenomenon in ecosystems with nutrient-deficient organogenic
soils. In the fourth site, a␣birch forest with a lush herb/shrub understorey, the differences between functional groups were
considerably smaller, and only the ERI species differed (by 1.1‰) from the NON species. Plants of all functional groups from
this site had nearly twice the leaf N concentration as that found in the same species at the other three sites. It is likely
that low inorganic N availability is a prerequisite for strong δ15N separation among functional groups. Both ECM roots and fruitbodies were 15N enriched compared to leaves which suggests that the difference in δ15N between plants with different kinds of mycorrhiza could be due to isotopic fractionation at the␣fungal-plant interface.
However, differences in δ15N between soil N forms absorbed by the plants could also contribute to the wide differences in plant δ15N found in most heath and forest tundra ecosystems. We hypothesize that during microbial immobilization of soil ammonium the
microbial N pool could become 15N-depleted and the remaining, plant-available soil ammonium 15N-enriched. The latter could be a main source of N for NON/AM plants which usually have high δ15N. In contrast, amino acids and other soil organic N compounds presumably are 15N-depleted, similar to plant litter, and ECM and ERI plants with high uptake of these N forms hence have low leaf δ15N. Further indications come from the δ15N of mosses and lichens which was similar to that of ECM plants. Tundra cryptogams (and ECM and ERI plants) have previously
been shown to have higher uptake of amino acid than ammonium N; their low δ15N might therefore reflect the δ15N of free amino acids in the soil. The concentration of dissolved organic N was 3–16 times higher than that of inorganic N
in the sites. Organic nitrogen could be an important N source for ECM and, in particular, ERI plants in heath and forest tundra
ecosystems with low release rate of inorganic N from the soil organic matter.
Received: 8 June 1997 / Accepted: 28 February 1998 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.
Robert G. Björk Leif Klemedtsson Ulf Molau Jan Harndorf Anja Ödman Reiner Giesler 《Plant and Soil》2007,294(1-2):247-261
The spatial distribution of organic soil nitrogen (N) in alpine tundra was studied along a natural environmental gradient,
covering five plant communities, at the Latnjajaure Field Station, northern Swedish Lapland. The five communities (mesic meadow,
meadow snowbed, dry heath, mesic heath, and heath snowbed) are the dominant types in this region and are differentiated by
soil pH. Net N mineralization, net ammonification, and net nitrification were measured using 40-day laboratory incubations
based on extractable NH4+ and NO3−. Nitrification enzyme activity (NEA), denitrification enzyme activity (DEA), amino acid concentrations, and microbial respiration
were measured for soils from each plant community. The results show that net N mineralization rates were more than three times
higher in the meadow ecosystems (mesic meadow 0.7 μg N g−1 OM day−1 and meadow snowbed 0.6 μg N g−1 OM day−1) than the heath ecosystems (dry heath 0.2 μg N g−1 OM day−1, mesic heath 0.1 μg N g−1 OM day−1 and heath snowbed 0.2 μg N g−1 OM day−1). The net N mineralization rates were negatively correlated to organic soil C/N ratio (r = −0.652, P < 0.001) and positively correlated to soil pH (r = 0.701, P < 0.001). Net nitrification, inorganic N concentrations, and NEA rates also differed between plant communities; the values
for the mesic meadow were at least four times higher than the other plant communities, and the snowbeds formed an intermediate
group. Moreover, the results show a different pattern of distribution for individual amino acids across the plant communities,
with snowbeds tending to have the highest amino acid N concentrations. The differences between plant communities along this
natural gradient also illustrate variations between the dominant mycorrhizal associations in facilitating N capture by the
characteristic functional groups of plants.
Responsible Editor: Bernard Nicolardot 相似文献
20.
Effect of activated charcoal and 6-benzyladenine on in vitro nitrogen uptake by Lagerstroemia indica 总被引:1,自引:0,他引:1
A sterile hydroponic culture system suitable for studying nitrogen (N) uptake ofLagerstroemia indica L.in vitro was developed. Four different treatments were assayed: with and without activated charcoal (AC and NAC, respectively), with
and without 50 μM of 6-benzyladenine (+BA and −BA, respectively). Medium pH, electrical conductivity (EC), NO3
− and NH4
+ concentrations were measured weekly. At the end of the culture, propagules were sampled and SPAD indices, and shoot and root
fresh weights were determined. Explants grown in media with activated charcoal were able to take up both NO3
− and NH4
+, although NH4
+ uptake was lower. Subsequently the pH of the media was maintained between 5.5–6.0. In treatments with no addition of activated
charcoal, NH4
+ uptake was preferential and the pH dropped to 3.1. Explants in these conditions were unable to raise the pH by taking up
NO3
−, especially when root morphogenesis was inhibited by addition of BA. Supply of this PGR produced root growth inhibition,
which was almost complete in the treatment without activated charcoal. This component significantly reduced the inhibitory
effect of 50 μM BA on root growth.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献