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1.
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
2.
Natural 15N abundance values were measured in needles, twigs, wood, soil, bulk precipitation, throughfall and soil water in a Douglas
fir (Pseudotsuga menziesii (Mirb.) and a Scots pine (Pinus sylvestris L.) stand receiving high loads of nitrogen in throughfall (>50 kg N ha−1 year−1). In the Douglas fir stand δ15N values of the vegetation ranged between −5.7 and −4.2‰ with little variation between different compartments. The vegetation
of the Scots pine stand was less depleted in 15N and varied from −3.3 to −1.2‰δ15N. At both sites δ15N values increased with soil depth, from −5.7‰ and −1.2‰ in the organic layer to +4.1‰ and +4.7‰ at 70 cm soil depth in the
Douglas fir and Scots pine stand, respectively. The δ15N values of inorganic nitrogen in bulk precipitation showed a seasonal variation with a mean in NH4
+-N of −0.6‰ at the Douglas fir stand and +10.8‰ at the Scots pine stand. In soil water below the organic layer NH4
+-N was enriched and NO3
−-N depleted in 15N, which was interpreted as being caused by isotope fractionation accompanying high nitrification rates in the organic layers.
Mean δ15N values of NH4
+ and NO3
− were very similar in the drainage water at 90 cm soil depth at both sites (−7.1 to −3.8‰). A dynamic N cycling model was
used to test the sensitivity of the natural abundance values for the amount of N deposition, the 15N ratio of atmospheric N deposited and for the intrinsic isotope discrimination factors associated with N transformation processes.
Simulated δ15N values for the N saturated ecosystems appeared particularly sensitive to the 15N ratio of atmospheric N inputs and discrimination factors during nitrification and mineralization. The N-saturated coniferous
forest ecosystems studied were not characterized by elevated natural 15N abundance values. The results indicated that the natural 15N abundance values can only be used as indicators for the stage of nitrogen saturation of an ecosystem if the δ15N values of the deposited N and isotope fractionation factors are taken into consideration. Combining dynamic isotope models
and natural 15N abundance values seems a promising technique for interpreting natural 15N abundance values found in these forest ecosystems.
Received: 5 May 1996 / Accepted: 10 April 1997 相似文献
3.
E. Wada R. Imaizumi Y. Kabaya T. Yasuda T. Kanamori G. Saito A. Nishimune 《Plant and Soil》1986,93(2):269-286
Summary Plants from agricultural and natural upland ecosystem were investigated for15N content to evaluate the role of symbiotic N2-fixation in the nitrogen nutrition of soybean. Increased yields and lower δ15N values of nodulating soybeansvs, non-nodulating isolines gave semi-quantitative estimates of N2 fixation. A fairly large discrepancy was found between estimations by δ15N and by N yield at 0 kg N/ha of fertilizer. More precise estimates were made by following changes in plant δ15N when fertilizer δ15N was varied near15N natural abundance level. Clearcut linear relationships between δ15N values of whole plants and of fertilizer were obtained at 30 kg N/ha of fertilizer for three kinds of soils. In experimental
field plots, nodulating soybeans obtained 13±1% of their nitrogen from fertilizer, 66±8% from N2 fixation and 21±10% from soil nitrogen in Andosol brown soil; 30%, 16% and 54% in Andosol black soil; 7%, 77% and 16% in
Alluvial soil, respectively. These values for N2 fixation coincided with each corresponding estimation by N yield method.
Other results include: 1)15N content in upland soils and plants was variable, and may reflect differences in the mode of mineralization of soil organics,
and 2) nitrogen isotopic discrimination during fertilizer uptake (δ15N of plant minus fertilizer) ranged from −2.2 to +4.9‰ at 0–30 kg N/ha of fertilizer, depending on soil type and plant species.
The proposed method can accurately and relatively simply establish the importance of symbiotic nitrogen fixation for soybeans
growing in agricultural settings. 相似文献
4.
The natural abundance of 15N in plant biomass has been used to infer how N dynamics change with elevated atmospheric CO2 and changing water availability. However, it remains unclear if atmospheric CO2 effects on plant biomass 15N are driven by CO2-induced changes in soil moisture. We tested whether 15N abundance (expressed as δ15N) in plant biomass would increase with increasing soil moisture content at two atmospheric CO2 levels. In a greenhouse experiment we grew sunflower (Helianthus annuus) at ambient and elevated CO2 (760 ppm) with three soil moisture levels maintained at 45, 65, and 85% of field capacity, thereby eliminating potential
CO2-induced soil moisture effects. The δ15N value of total plant biomass increased significantly with increased soil moisture content at both CO2 levels, possibly due to increased uptake of 15N-rich organic N. Although not adequately replicated, plant biomass δ15N was lower under elevated than under ambient CO2 after adjusting for plant N uptake effects. Thus, increases in soil moisture can increase plant biomass δ15N, while elevated CO2 can decrease plant biomass δ15N other than by modifying soil moisture. 相似文献
5.
Correlations between foliar δ15N and nitrogen concentrations may indicate plant-mycorrhizal interactions 总被引:1,自引:0,他引:1
Nitrogen isotope measurements may provide insights into changing interactions among plants, mycorrhizal fungi, and soil processes
across environmental gradients. Here, we report changes in δ15N signatures due to shifts in species composition and nitrogen (N) dynamics. These changes were assessed by measuring fine
root biomass, net N mineralization, and N concentrations and δ15N of foliage, fine roots, soil, and mineral N across six sites representing different post-deglaciation ages at Glacier Bay,
Alaska. Foliar δ15N varied widely, between 0 and –2‰ for nitrogen-fixing species, between 0 and –7‰ for deciduous non-fixing species, and between
0 and –11‰ for coniferous species. Relatively constant δ15N values for ammonium and generally low levels of soil nitrate suggested that differences in ammonium or nitrate use were
not important influences on plant δ15N differences among species at individual sites. In fact, the largest variation among plant δ15N values were observed at the youngest and oldest sites, where soil nitrate concentrations were low. Low mineral N concentrations
and low N mineralization at these sites indicated low N availability. The most plausible mechanism to explain low δ15N values in plant foliage was a large isotopic fractionation during transfer of nitrogen from mycorrhizal fungi to plants.
Except for N-fixing plants, the foliar δ15N signatures of individual species were generally lower at sites of low N availability, suggesting either an increased fraction
of N obtained from mycorrhizal uptake (f), or a reduced proportion of mycorrhizal N transferred to vegetation (T
r). Foliar and fine root nitrogen concentrations were also lower at these sites. Foliar N concentrations were significantly
correlated with δ15N in foliage of Populus, Salix, Picea, and Tsuga heterophylla, and also in fine roots. The correlation between δ15N and N concentration may reflect strong underlying relationships among N availability, the relative allocation of carbon
to mycorrhizal fungi, and shifts in either f or T
r.
Received: 14 December 1998 / Accepted: 16 August 1999 相似文献
6.
Variations in crop grain and soil N isotope composition (δ15N) in relation to liquid hog manure (δ15N of total N was +5.1‰), solid cattle manure (+7.9‰) and chemical fertilizer (+0.7‰ for urea and −1.9‰ for ammonium phosphate)
applications, and control (no fertilizer application) were examined through a 4-year crop rotation under field conditions.
Canola (Brassica napus), hull-less barley (Hordeum vulgare), wheat (Triticum aestivum), and canola were grown sequentially from 2000 (year 1) to 2003 (year 4). From year 2, hog manure or chemical fertilizers,
but not cattle manure, treatments increased grain N concentrations over the control. Grain δ15N (+0.3 to +2.5‰) of crops applied with chemical fertilizers was lower than those in the other treatments, reflecting the
effects of the N source with a lower δ15N, while the manure treatments tended to increase grain δ15N. The higher grain δ15N of crops applied with hog manure (+5.6 to +8.4‰) than those applied with cattle manure (+2.2 to +4.1‰) reflected the higher
N availability of liquid hog manure (up to 70% as NH
4
+
) than solid cattle manure (99% organic N) and higher potentials for ammonia volatilization loss in hog manure rather than
differences in manure δ15N signatures. Soil total- and extractable-N concentrations and δ15N tended to vary with the application of N sources with different N isotope composition and availability. Our study expanded
the application of the δ15N technique for detecting N source (organic vs chemical) effects on N isotopic composition to field conditions and across
a 4-year rotation, and revealed that N availability played a greater role than the δ15N signature of N sources in determining crop δ15N under the studied conditions.
Section Editor: H. Lambers 相似文献
7.
Tracing the Sources of Exported Nitrate in the Turkey Lakes Watershed Using 15N/14N and 18O/16O isotopic ratios 总被引:3,自引:0,他引:3
John Spoelstra Sherry L. Schiff Richard J. Elgood Ray G. Semkin Dean S. Jeffries 《Ecosystems》2001,4(6):536-544
Nitrate produced by bacterially mediated nitrification in soils is isotopically distinct from atmospheric nitrate in precipitation.
15N/14N and 18O/16O isotopic ratios of nitrate can therefore be used to distinguish between these two sources of nitrate in surface waters and
groundwaters. Two forested catchments in the Turkey Lakes Watershed (TLW) near Sault Ste. Marie, Ontario, Canada were studied
to determine the relative contributions of atmospheric and microbial nitrate to nitrate export. The TLW is reasonably undisturbed
and receives a moderate amount of inorganic nitrogen bulk deposition (8.7 kg N · ha−1· yr−1) yet it exhibits unusually low inorganic nitrogen retention (average = 65% of deposition). The measured isotopic ratios for
nitrate in precipitation ranged from +35 to +59‰ (VSMOW) for δ18O and −4 to +0.8‰ (AIR) for δ15N. Nitrate produced from nitrification at the TLW is expected to have an average isotope value of approximately −1.0‰ for
δ18O and a value of about 0 to +6‰ for δ15N, thus, the isotopic separation between atmospheric and soil sources of nitrate is substantial. Nitrate produced by nitrification
of ammonium appears to be the dominant source of the nitrate exported in both catchments, even during the snowmelt period.
These whole catchment results are consistent with the results of small but intensive plot scale studies that have shown that
the majority of the nitrate leached from these catchments is microbial in origin. The isotopic composition of stream nitrate
provides information about N-cycling in the forested upland and riparian zones on a whole catchment basis.
Received 5 October 1999; accepted 18 August 2000 相似文献
8.
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
9.
Since the middle of the 19th century, the area covered by forests in France has doubled. These new forests grow on previous
agricultural lands. We have studied the influence of this agricultural history on the 15N abundance of present-day forests planted on farmlands in the Vosges mountains (north-eastern France) between 1898 and 1930.
Different types of land use were identified from old cadastres (1814–1836) of 16 farms. Ancient forests adjacent to farmlands
were used as controls. Former pastures, meadows, croplands, gardens and ancient forests were compared for soil δ15N (fraction <50 μm and total soil), C/N, P and N content and fern (Dryopteris carthusiana) δ15N. The mean δ15N of soil increased in the order ancient forests (+0.0‰)<pastures (+1.4‰)<croplands (+1.6‰)<meadows (+2.5‰)<gardens (+3.8‰).
This increase in soil δ15N with the intensity of former land use was related to the former input of 15N-enriched manure, and to an activation of soil nitrification leading to 15N-depleted nitrate export on previously manured parcels. Fern δ15N increased in the same order as soil δ15N in relation to past land use. The mean δ15N of fern in ancient forests (–4.4‰) and former pastures (–3.4‰) was 5‰ lower than soil δ15N and the two variables were strongly correlated. The δ15N of fern in formerly manured parcels varied little (cropland: –2.7‰, meadows: –2.6‰ and gardens: –2.2‰) and independently
of soil δ15N, suggesting that the soil sources of fern N differed between unmanured and manured parcels. Understorey plant δ15N and soil δ15N appear to be excellent tracers of previous land use in forests, and could be used in historical studies. The persistence
of high isotopic ratios in previously manured parcels, almost a century after afforestation, suggests a long-term influence
of former land use on the N cycle in forest soils.
Received: 22 January 1999 / Accepted: 22 July 1999 相似文献
10.
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
11.
Nitrogen and carbon isotope responses of Chinese cabbage and chrysanthemum to the application of liquid pig manure 总被引:2,自引:0,他引:2
Sang-Sun Lim Woo-Jung Choi Jin-Hyeob Kwak Jae-Woon Jung Scott X. Chang Han-Yong Kim Kwang-Sik Yoon Soo-Myung Choi 《Plant and Soil》2007,295(1-2):67-77
The effects of the liquid pig manure (LM) used in organic farming on the natural abundance of 15N and 13C signatures in plant tissues have not been studied. We hypothesized that application of LM will (1) increase δ15N of plant tissues due to the high δ15N of N in LM as compared with soil N or inorganic fertilizer N, and (2) increase δ13C of plant tissues as a result of high salt concentration in LM that decreases stomatal conductance of plants. To test these
hypotheses, variations in the δ15N and δ13C of Chinese cabbage (Brassica campestris L.) and chrysanthemum (Chrysanthemum morifolium Ramatuelle) with two different LMs (with δ15N of +15.6 and +18.2‰) applied at two rates (323 and 646 kg N ha-1 for cabbage and 150 and 300 kg N ha-1 for chrysanthemum), or urea (δ15N = -2.7‰) applied at the lower rate above for the respective species, in addition to the control (no N input) were investigated
through a 60-day pot experiment. Application of LM significantly increased plant tissue δ15N (range +9.4 to +14.9‰) over the urea (+3.2 to +3.3‰) or control (+6.8 to 7.7‰) treatments regardless of plant species, strongly
reflecting the δ15N of the N source. Plant tissue δ13C were not affected by the treatments for cabbage (range −30.8 to −30.2‰) or chrysanthemum (−27.3 to −26.8‰). However, cabbage
dry matter production decreased while its δ13C increased with increasing rate of LM application or increasing soil salinity (P < 0.05), suggesting that salinity stress caused by high rate of LM application likely decreased stomatal conductance and
limited growth of cabbage. Our study expanded the use of the δ15N technique in N source (organic vs. synthetic fertilizer) identification and suggested that plant tissue δ13C maybe a sensitive indicator of plant response to salinity stress caused by high LM application rates. 相似文献
12.
We used the natural abundance of 15N in soils in forests, pastures and cultivated lands in the Menagesha and Wendo-Genet areas of Ethiopia to make inferences
about the N cycles in these ecosystems. Since we have described the history of these sites based on variations in 13C natural abundance, patterns of δ15N and δ13C values were compared to determine if shifts of 15N correlate with shifts of vegetation. At Menagesha, a > 500-yr-old planted forest, we found δ15N values from −8.8 to +3.5‰ in litter, from −3.5 to +4.5‰ in 0–10 cm soil layer, and from −1.5 to +6.8‰ at >20 cm soil depth.
The low δ15N in litter and surface mineral soils suggests that a closed N cycle has operated for a long time. At this site, the low δ13C of the surface horizon and the high δ13C of the lower soil horizons is clear evidence of a long phase of C4 grass dominance or cultivation of C4 crops before the establishment of the forest >500 years ago. In contrast, at Wendo-Genet, high δ13C of soils reveals that most of the land has been uncovered by forests until recently. Soil δ15N was high throughout (3.4–9.8‰), and there were no major differences between forested, cultivated and pasture soils in δ15N values of surface mineral soils. The high δ15N values suggest that open N cycles operate in the Wendo-Genet area. From the points of view of soil fertility management,
it is interesting that tall forest ecosystems with relatively closed N cycling could be established on the fairly steep slopes
at Menagesha after a long period of grass vegetation cover or cultivation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
13.
Monitoring plant physiological characteristics to evaluate mine site revegetation: A case study from the wet-dry tropics of northern Australia 总被引:1,自引:0,他引:1
Biologically driven markers or monitors were used to evaluate plant and ecosystem health of uranium-mining affected sites.
Plant water, nitrogen (N) and phosphorus (P) status were used to measure physiological characteristics of tree and shrub species
at sites perturbed by mining activities (waste rock dumps: WRD 1, WRD 2; mine wastewater irrigated woodland) and of species
at undisturbed woodland (tropical savanna). Plant water status was evaluated by measuring leaf relative water content (RWC)
and carbon isotope discrimination (δ13C). Leaf RWC varied significantly (P<0.0001) between wet and dry season in species at the woodland sites with higher RWC in
the wet season compared to the dry season. No seasonal differences were observed in RWC in species at the WRDs. Leaf δ13C was similar in species at woodland sites and WRD 2 (−28.8 to −28.1‰) but was significantly (P<0.05) lower in species at
WRD 1 (−27.6‰). This suggests that species at WRD 1 had a lower water availability and/or lower water use compared to species
at all other sites. WRD substrate had an up to 4-orders of magnitude greater availability of inorganic phosphate (Pi) compared
to woodland soil as determined using in situ ion exchange resin. Pi concentrations in xylem sap of species at WRDs were 2-
to 3-fold higher compared to species at woodland sites. Plant nitrate reductase (NR) activity was low in most species at woodland
and WRD 1. In contrast, Eucalyptus and Acacia species had high NR activities of up to 300–700 pkat g-1 fw at WRD 2 indicating that these species had greater nitrate use than species at all other sites. Nitrate availability in
the top five cm of the profile, as determined using in situ ion exchange resins, increased at all sites in the wet season,
but no significant differences were observed between sites using this method. However, traditional soil analysis revealed
that WRD substrate had a 2-times higher nitrate content (0 to 1000 mm depth) compared to woodland soil. Thus, it is likely
that plants at WRD2 accessed nitrate from deeper parts of the profile. Proline, an indicator of plant stress, was found in
appreciable quantities in leaves of herbaceous species but not in woody species. Soil and leaf δ15N were measured to investigate N-cycling and the contribution of diazotrophic N2 fixation to plant N nutrition. Soil δ15N values were highest and most variable at WRD 2 (6.2‰) compared to all other sites (irrigated woodland 3.1‰, undisturbed
woodland 2.5‰, WRD 1 0.9‰). This may indicate that N-turnover and nitrification was greatest at WRD 2 leading to greater 15N enrichment of soil N. At all sites, Acacia species were nodulated and putatively fixing N2. With the exception of WRD 2 where leaf δ15N of Acacia species averaged 0.9‰, Acacia species had 15N depleted values characteristic of species that receive N derived from N2 fixation (−0.8 to −0.6‰).
Eucalyptus species at the woodland also had 15N depleted values (average −0.4‰) but 15N enriched values (0.3 to 1.8‰) at the three mining affected sites. The results show that for the plants studied foliar δ15N could not be used as an unequivocal measure of plant N sources. The results suggest that biomonitoring of plant and ecosystem
health has potential in evaluating performance of mine site revegetation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
15N abundances of current needles of Norway spruce collected during 23 yrs of a forest fertilization experiment were studied
in order to follow ecosystem gains and losses of N. Unlabelled ammonium nitrate at four rates (N0–N3), phosphorus at three
rates (P0–P2), and potassium plus other elements including micronutrients at two rates (K0–K1), had been applied to plots
in a complete factorial design. Nitrogen had been applied annually at average rates of 0, 34, 68 and 102 kg N ha-1 yr-1. Tree growth had responded positively to additions of N, but the response was remarkably more positive to the N2P2K1 treatment.
In N1 treatments, δ15N (‰) declined over time. This was consistent with an earlier study, and should reflect a change in 15N abundance towards that of fertilizer N (minus discrimination during uptake), which in turn means accretion of most of the
N added. As in the earlier study, in which N3 plots lost most of the N added, the present N3 plots showed an increasing δ15N (‰). This pattern was not significantly affected by additions of P and K plus other elements, although a weak negative effect
of P on N accretion was indicated, i.e. there was a tendency δ15N (‰) to be higher when P was added. This, and another recent result based on an N budget, shows that so-called revitalization
fertilization may well increase growth of trees, but also promotes losses of N from the ecosystem. As in the previous study,
a decline in δ15N (‰) on control plots provided evidence of contamination. Given a removal of 100 kg N ha-1 at stem harvest and a leaching of 2 kg N ha-1 yr-1, our data on 15N suggest that a load of 9 kg N ha-1 yr-1 would saturate the ecosystem after 100 years. This load is only about twice the annual deposition at the site. 相似文献
15.
Abstract
Stable isotope ratios of terrestrial ecosystem nitrogen (N) pools reflect internal processes and input–output balances. Disturbance
generally increases N cycling and loss, yet few studies have examined ecosystem δ15N over a disturbance-recovery sequence. We used a chronosequence approach to examine N distribution and δ15N during forest regrowth after agricultural abandonment. Site ages ranged from 10 to 115 years, with similar soils, climate,
land-use history, and overstory vegetation (white pine Pinus strobus). Foliar N and δ15N decreased as stands aged, consistent with a progressive tightening of the N cycle during forest regrowth on agricultural
lands. Over time, foliar δ15N became more negative, indicating increased fractionation along the mineralization–mycorrhizal–plant uptake pathway. Total
ecosystem N was constant across the chronosequence, but substantial internal N redistribution occurred from the mineral soil
to plants and litter over 115 years (>25% of ecosystem N or 1,610 kg ha−1). Temporal trends in soil δ15N generally reflected a redistribution of depleted N from the mineral soil to the developing O horizon. Although plants and
soil δ15N are coupled over millennial time scales of ecosystem development, our observed divergence between plants and soil suggests
that they can be uncoupled during the disturbance-regrowth sequence. The approximate 2‰ decrease in ecosystem δ15N over the century scale suggests significant incorporation of atmospheric N, which was not detected by traditional ecosystem
N accounting. Consideration of temporal trends and disturbance legacies can improve our understanding of the influence of
broader factors such as climate or N deposition on ecosystem N balances and δ15N.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
16.
The importance of facilitative processes due to the presence of nitrogen-fixing legumes in temperate grasslands is a contentious
issue in biodiversity experiments. Despite a multitude of studies of fertilization effects of legumes on associated nonfixers
in agricultural systems, we know little about the dynamics in more diverse systems. We hypothesised that the identity of target
plant species (phytometers) and the diversity of neighbouring plant species would affect the magnitude of such positive species
interactions. We therefore sampled aboveground tissues of phytometers planted into all plots of a grassland biodiversity–ecosystem
functioning experiment and analysed their N concentrations, δ15N values and biomasses. The four phytometer species (Festuca pratensis, Plantago lanceolata, Knautia arvensis and Trifolium pratensis) each belonged to one of the four plant functional groups used in the experiment and allowed the effects of diversity on
N dynamics in individual species to be assessed. We found significantly lower δ15N values and higher N concentrations and N contents (amount of N per plant) in phytometer species growing with legumes, indicating
a facilitative role for legumes in these grassland ecosystems. Our data suggest that the main driving force behind these facilitative
interactions in plots containing legumes was reduced competition for soil nitrate (“nitrate sparing”), with apparent N transfer
playing a secondary role. Interestingly, species richness (and to a lesser extent functional group number) significantly decreased
δ15N values, N concentrations and N content irrespective of any legume effect. Possible mechanisms behind this effect, such as
increased N mineralisation and nitrate uptake in more diverse plots, now need further investigation. The magnitude of the
positive interactions depended on the identity of the phytometer species. Evidence for increased N uptake in communities containing
legumes was found in all three nonlegume phytometer species, with a subsequent strong increase in biomass in the grass F. pratensis across all diversity levels, and a lesser biomass gain in P. lanceolata and K. arvensis. In contrast, the legume phytometer species T. pratense was negatively affected when other legumes were present in their host communities across all diversity levels. 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.
El Amin Yousif Raddad Ahmed Ali Salih Mohamed Ahmed El Fadl Vesa Kaarakka Olavi Luukkanen 《Plant and Soil》2005,275(1-2):261-269
The symbiotic biological N2fixation by Acacia senegal was estimated using the 15N natural abundance (δ
15N) procedure on eight provenances collected from different environments and soil types grown in a clay soil in the Blue Nile
region, Sudan. Balanites aegyptiaca (a non-legume) was used as a non-N2-fixing reference plant to allow 15N-based estimates of the proportion of the Acacia N derived from atmospheric N2 (Ndfa) to be calculated. Results show variation in leaf δ
15N between A. senegal and the reference plant and among years. The relative δ
15N values (‰) were higher in B. aegyptiaca than in the N2-fixing acacia provenances. Provenances originally collected from clay soils fixed little N in the first year, but the amount
fixed increased as the trees aged. All provenances showed a decrease in δ
15N with age. The Ndfa varied between 24% (Mazmoom provenance) and 61% (Rahad provenance) 4 years after planting. There was no significant difference
in δ
15N between provenance groups based on soil type or rainfall at original growing site. The amount of Ndfa increased significantly with age in all provenances. The above-ground contribution of fixed N to foliage growth in a 4-year-old
A. senegal was highest in the Rahad sand–soil provenance (46.7 kg N ha−1) and lowest in the Mazmoom clay-soil provenance (28.7 kg N ha−1). Our study represents the first use of the δ
15N method for estimating the N input by A. senegal to the clay plain soils of the gum belt in the Sudan. 相似文献
19.
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
20.
15N natural abundances and N use by tundra plants 总被引:2,自引:0,他引:2
Plant species collected from tundra ecosystems located along a north-south transect from central Alaska to the north coast of Alaska showed large and consistent differences in 15N natural abundances. Foliar 15N values varied by about 10% among species within each of two moist tussock tundra sites. Differences in 15N contents among species or plant groups were consistent across moist tussock tundra at several other sites and across five other tundra types at a single site. Ericaceous species had the lowest 15N values, ranging between about –8 to –6. Foliar 15N contents increased progressively in birch, willows and sedges to maximum 15N values of about +2 in sedges. Soil 15N contents in tundra ecosystems at our two most intensively studied sites increased with depth and 15N values were usually higher for soils than for plants. Isotopic fractionations during soil N transformations and possibly during plant N uptake could lead to observed differences in 15N contents among plant species and between plants and soils. Patterns of variation in 15N content among species indicate that tundra plants acquire nitrogen in extremely nutrient-poor environments by competitive partitioning of the overall N pool. Differences in plant N sources, rooting depth, mycorrhizal associations, forms of N taken up, and other factors controlling plant N uptake are possible causes of variations in 15N values of tundra plant species. 相似文献