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1.
Understanding the phosphate oxygen isotope (δ18O‐PO4) composition of bedrock phosphate sources is becoming ever more important, especially in areas of soil research which use this isotope signature as a proxy for biological cycling of phosphorus (P). For many of these studies, obtaining a sample of the source bedrock or applied mineral fertiliser for isotope analysis is impossible; meaning there is now a demand for a comprehensive characterisation of global bedrock δ18O‐PO4 to support this work. Here we compile δ18O‐PO4 data from a wide range of global bedrocks, including 56 new values produced as part of this study and a comprehensive overview of those within the previously existing literature. We present δ18O‐PO4 data from the range of major phosphatic lithologies alongside as much metadata for the samples as could be gathered. Much of the data comes from bedrocks of marine sedimentary origin (< 1 Ma = > +22‰, > 540 Ma = ≈ +12‰), but we also present data from bedrocks associated with guano (range: +19.5 to +15‰) and igneous deposits (range: +12 to –0.8‰), both of which have distinct δ18O‐PO4 signatures due to their formation mechanisms. We show that where repeat measurements of the same formation have been undertaken, regardless of method or exact sample location, there is an average within formation error of ± 1.25‰. This is important, as is constitutes a reasonable level of uncertainty for phosphorus cycling studies which need to estimate bedrock δ18O‐PO4 composition based on the literature. In combination, this data set presents 284 δ18O‐PO4 values from 56 countries; a comprehensive starting point for researchers interested in understanding bedrock end member δ18O‐PO4.  相似文献   

2.
Land application of animal wastes from intensive grassland farming has caused growing environmental problems during the last decade. This study aimed to elucidate the short‐term sequestration of slurry‐derived C and N in a temperate grassland soil (Southwest England) using natural abundance 13C and 15N stable isotope techniques. Slurry was collected from cows fed either on perennial ryegrass (C3) or maize (C4) silages. 50 m3 ha—1 of each of the obtained C3 or C4 slurries (δ13C = —30.7 and —21.3‰, δ15N = +12.2 and + 13.8 ‰, respectively) were applied to a C3 soil with δ13C and δ15N values of —30.0 ± 0.2‰ and + 4.9 ± 0.3‰, respectively. Triplicate soil samples were taken from 0—2, 2—7.5, and 7.5—15 cm soil depth 90 and 10 days before, at 2 and 12 h, as well as at 1, 2, 4, 7, and 14 days after slurry application and analyzed for total C, N, δ13C, and δ15N. No significant differences in soil C and N content were observed following slurry application using conventional C and N analysis techniques. However, natural abundance 13C and 15N isotope analysis allowed for a sensitive temporal quantification of the slurry‐derived C and N sequestration in the grassland soil. Our results showed that within 12 hours more than one‐third of the applied slurry C was found in the uppermost soil layer (0—2 cm), decreasing to 18% after 2 days, but subsequently increasing to 36% after 2 weeks. The tentative estimate of slurry‐derived N in the soil suggested a decrease from 50% 2 hours after slurry application to only 26% after 2 weeks, assuming that the increase in δ15N of the slurry plots compared to the control is proportional to the amount of slurry‐incorporated N. We conclude that the natural abundance tracer technique can provide a rapid new clue to the fate of slurry in agricultural C and N budgets, which is important for environmental impacts, farm waste management, and climate change studies.  相似文献   

3.
Phosphorus (P) cycles rapidly in lowland tropical forest soils, but the process have been proven difficult to quantify. Recently it was demonstrated that valuable data on soil P transformations can be derived from the natural abundance of stable oxygen isotopes in phosphate (δ18OP). Here, we measured the δ18OP of soils that had received long-term nutrient additions (P, nitrogen, and potassium) or litter manipulations in lowland tropical forest in Panama and performed controlled incubations of fresh soils amended with a single pulse of P. To detect whether δ18OP values measured in the incubations apply also for soils in the field, we examined the δ18OP values after rewetting dry soils. In the incubations, resin-P δ18OP values converged to ∼3.5‰ above the expected isotopic equilibrium with soil water. This contrasts with extra-tropical soils in which the δ18OP of resin-P matches the expected equilibrium with soil water. Identical above-equilibrium resin-P δ18OP values were also found in field soils that did not receive P additions or extra litter. We suggest that the 3.5‰ above-equilibrium δ18OP values reflect a steady state between microbial uptake of phosphate (which enriches the remaining phosphate with the heavier isotopologues) and the release of isotopically equilibrated cell internal phosphate back to the soil. We also found that soil nutrient status affected the microbial turnover rate because in soils that had received chronic P addition, the original δ18OP signature of the fertilizer was preserved for at least eight weeks, indicating that the off-equilibrium δ18OP values produced during microbial phosphate turnover was not imprinted in these soils. Overall, our results demonstrate that ongoing microbial turnover of phosphate mediates its biological availability in lowland tropical soils.  相似文献   

4.
Soil phosphates exchange oxygen atoms rapidly with soil water once recycled by intracellular enzymes, thereby approaching an equilibrium δ18OP signature that depends on ambient temperature and the δ18OW signature of soil water. We hypothesized that in the topsoil, phosphates reach this equilibrium δ18OP signature even if amended by different fertilizers. In the subsoil, however, there might be phosphates with a smaller δ18OP value than that represented by the isotopic equilibrium value, a condition that could exist in the case of limited biological P cycling only. We tested these hypotheses for the HCl‐extractable P pool of the Hedley fractionation scheme of arable soil in Germany, which integrates over extended time‐scales of the soil P cycle. We sampled several types of fertilizer, the surface soil that received these fertilizer types and composites from a Haplic Luvisol depth profile under long‐term agricultural practice. Organic fertilizers had significantly smaller δ18OP values than mineral fertilizers. Intriguingly, the fields fertilized organically also tended to have smaller δ18OP signatures than other types of surface soil, which calls into question full isotopic equilibrium at all sites. At depths below 50 cm, the soil δ18OP values were even depleted relative to the values calculated for isotopic equilibrium. This implies that HCl‐extractable phosphates in different soil horizons are of different origins. In addition, it supports the assumption that biological cycling of P by intracellular microbial enzymes might have been relatively inefficient in the deeper subsoil. At depths of 50–80 cm, there was a transition zone of declining δ18OP values, which might be regarded as the first evidence that the degree of biological P cycling changed at this depth interval.  相似文献   

5.
Soils comprise a critical interface between the atmosphere, lithosphere, hydrosphere and biosphere, and play a major role in the cycling of nitrogen (N), an element crucial to plant growth. Isotope techniques constitute a powerful tool to study the origin and fate of N compounds (e.g. NO3−) within the environment including soils. The objective of our study was to test the usefulness of the isotope composition of soil NO3− extracted with 2 M KCl (soil NO3) as a tool to investigate the origin and fate of NO3− in the environment. Specifically issues related to repeat extractions, crop type, length of fertilization, and soil depth were addressed. Soils from four contrasting agricultural management regimes were sampled. Within the relatively confined study area (4 ha), the isotopic compositions of soil NO3 differed markedly due to management treatments (up to 6 and 17‰ for δ15N and δ18O, respectively), but were repeatable among replicate plots (±1‰). Differences in both δ15N and δ18O values were observed between legume and non-legume treatments, as well as fertilized versus non-fertilized treatments, which were larger than the variability observed between replicate plots. Differences in the isotopic composition of extractable soil nitrate were not limited to the surface layer, but also occurred within deeper soil layers. This study indicates that the analysis of the natural abundance stable isotope composition of soil NO3 may provide a promising additional tool for tracing the origin and fate of NO3− in the soil zone.  相似文献   

6.
The availability of C and N to the soil microbial biomass is an important determinant of the rates of soil N transformations. Here, we present evidence that changes in C and N availability affect the 15N natural abundance of the microbial biomass relative to other soil N pools. We analysed the 15N natural abundance signature of the chloroform‐labile, extractable, NO3–, NH4+ and soil total N pools across a cattle manure gradient associated with a water reservoir in semiarid, high‐desert grassland. High levels of C and N in soil total, extractable, NO3–, NH4+ and chloroform‐labile fractions were found close to the reservoir. The δ15N value of chloroform‐labile N was similar to that of extractable (organic + inorganic) N and NO3– at greater C availability close to the reservoir, but was 15N‐enriched relative to these N‐pools at lesser C availability farther away. Possible mechanisms for this variable 15N‐enrichment include isotope fractionation during N assimilation and dissimilation, and changes in substrate use from a less to a more 15N‐enriched substrate with decreasing C availability.  相似文献   

7.
Laser spectroscopy is an emerging technique to analyze the stable isotopic composition of soil-respired CO2 (δ13Cresp, δ18Oresp) in situ and at high temporal resolution. Here we present the first application of a quantum cascade laser-based spectrometer (QCLS) in a closed soil-chamber system to determine simultaneously δ13Cresp and δ18Oresp. In a Swiss beech forest, a total of 90 chamber measurements with 20 min sampling time each were performed. The instrument measured the δ13C and δ18O of the CO2 in the chamber headspace at every second with a precision of 0.25‰, resulting in Keeling plots with 1200 data points. In addition, we calculated δ13Cresp directly from the flux ratio of 13CO2 and 12CO2. The flux-ratio values were 0.8‰ lower than the Keeling plot intercepts when the flux rates were derived from quadratic curve fits of the CO2 increase. The δ18O-Keeling plots showed a significant bending very likely due to the equilibration of chamber CO2 with the 18O of surface soil water. Therefore, we used a quadratic curve fit of the Keeling plots to estimate δ18Oresp. Our results also revealed that δ13Cresp was not constant throughout the CO2 accumulation in the closed soil chambers: there were significant but non-systematic variations in δ13Cresp for the first 10 min, and systematic shifts in δ13Cresp of on average 1.9 ‰ in the second part of the 20-min measurements. These biases were probably caused by non-steady-state conditions in the soil-chamber system. Our study illustrates that the high temporal resolution of QCLS measurements allows the detection of non-linearities in the isotopic effluxes of CO2 from the soil due to soil-chamber feedbacks. This information can be used to improve the estimates for δ13Cresp and δ18Oresp.  相似文献   

8.
Abstract

Isotopic nitrogen (N) research techniques may be required in watershed studies to determine the impact of landscape position on fertilizer efficiency and the soil supplying power. However, traditional approaches using I5N labeled fertilizer may not be suitable when farmer equipment is used. The δ15N natural abundance isotopic approach has been used to evaluate N cycling in watersheds. The objectives of this study were to measure the precision of the δ15N measurement by the Europa 20–20 ratio mass spectrometer (Europa Scientific Ltd, UK), and to compare the difference and δ15N approaches for measuring fertilizer use by maize (Zea mays). A replicated field study containing two different N rates (0 and 15.7 g N m‐2) were used for the study. Maize samples were collected at the 8th‐leaf, silking, and plant maturity in 1992 and 1993. Samples were dried (80°C), ground (<1‐mm), weighed (stover 12 mg and grain 3 mg), and analyzed fortotal N and δ15N. Fertilizer utilization at the three growth stages was determined using the natural abundance δ15N and nonisotopic difference (fertilizer‐control) techniques. During the study, the Europa 20–20 ratio mass spectrometer (Europa Scientific Ltd, UK) analyzed over a 100 samples a day and had consumable costs of less than $2.00 per sample. The standard deviations of the mean were less than 0.11 and 0.21 %o in 51 and 77% of the stover samples, respectively. In 1992, grain yields were not influenced by N fertilizer additions, while in 1993 grain yields were increased by N fertilizer. The difference method estimated that in 1992, 16% of the N fertilizer was utilized by the crop, while the natural abundance δ15N approach estimated that 36% of the fertilizer N was used by the crop. Differences between calculated values by the two techniques resulted from the difference method calculating net fertilizer use, while the δ15N approach calculated fertilizer contained in the plant. Because the δ15N approach estimates fertilizer use, this approach can be used to calculate soil N contained in the plant. In watershed studies, this information may provide the tools needed to evaluate N use in responsive and nonresponsive sites within a field. This research shows that the δ15N method compliments the difference method, can be used to measure actual fertilizer use when farmer equipment is used, and that the Europa 20–20 ratio mass spectro‐meter (Europa Scientific Ltd, UK) has acceptable precision for the δ15N natural abundance approach.  相似文献   

9.
To determine whether NO3 ? concentration pulses in surface water in early spring snowmelt discharge are due to atmospheric NO3 ?, we analyzed stream δ15N-NO3 ? and δ18O-NO3 ? values between February and June of 2001 and 2002 and compared them to those of throughfall, bulk precipitation, snow, and groundwater. Stream total Al, DOC and Si concentrations were used to indicate preferential water flow through the forest floor, mineral soil, and ground water. The study was conducted in a 135-ha subcatchment of the Arbutus Watershed in the Huntington Wildlife Forest in the Adirondack Region of New York State, U.S.A. Stream discharge in 2001 increased from 0.6 before to 32.4 mm day?1 during snowmelt, and element concentrations increased from 33 to 71 μmol L?1 for NO3 ?, 3 to 9 μmol L?1 for total Al, and 330 to 570 μmol L?1 for DOC. Discharge in 2002 was variable, with a maximum of 30 mm day?1 during snowmelt. The highest NO3 ?, Al, and DOC concentrations were 52, 10, and 630 μmol L?1, respectively, and dissolved Si decreased from 148 μmol L?1 before to 96 μmol L?1 during snowmelt. Values of δ15N and δ18O of NO3 ? in stream water were similar in both years. Stream water, atmospherically-derived solutions, and groundwaters had overlapping δ15N-NO3 ? values. In stream and ground water, δ18O-NO3 ? values ranged from +5.9 to +12.9‰ and were significantly lower than the +58.3 to +78.7‰ values in atmospheric solutions. Values of δ18O-NO3 ? indicating nitrification, increase in Al and DOC, and decrease in dissolved Si concentrations indicating water flow through the soil suggested a dilution of groundwater NO3 ? by increasing contributions of forest floor and mineral soil NO3 ? during snowmelt.  相似文献   

10.
Photosynthetically derived rhizodeposits are an important source of carbon (C) for microbes in root vicinity and can influence the microbial community dynamics. Pulse labeling of carbon dioxide (13CO2) coupled with stable isotope probing techniques have potential to track recently fixed photosynthate into rhizosphere microbial taxa. Therefore, the present investigation assessed the microbial community change associated with the rhizosphere and bulk soil in Jatropha curcas L. (a biofuel crop) by combining phospholipid fatty acid (13C-PLFA) profiling using a stable isotope 13CO2 labeling approach. The labeling (13C) took place after 45 days of germination, PLFAs were extracted from both soils (rhizosphere and bulk) after 1 and 20 days pulse labeling and analyzed by gas chromatography-isotope ratio mass spectrometry. There was no significant temporal effect on the PLFA profiles in the bulk soil, but significantly increased abundance of Gram positive (i15:0) and Gram negative (16:1ω7c and 16:1ω5c) biomarkers was observed in the rhizosphere soil from day 1 to day 20 after labeling. The Gram negative (16:1ω7c) decreased and fungal (18:2ω6,9c) increased significantly in rhizospheric soil compared to bulk soil after day 1 of labeling. Whereas, after 20 days of labeling, the Gram negative biomarker (16:1ω7c and 18:1ω7c) decreased and Gram positive (a15:0) increased significantly in rhizospheric soil compared to bulk soil. One day following labeling, i15:0, a15:0, i16:0, 16:1ω5c, 16:0, i17:0, a17:0, 18:2ω6,9c, 18:1ω9c, and 18:0 PLFAs were significantly more enriched in δ13C in the rhizosphere than in the bulk soil. Twenty days after labeling, 16:1ω5c (Gram negative) and 18:2ω6,9c (fungal) were significantly more enriched in δ13C in the rhizosphere than in the bulk soil. These results shows the effectives of PLFA coupled using the pulse chase labeling technique to examine the microbial community changes in response to recently fixed photosynthetic C flow in rhizodeposits.  相似文献   

11.
Amino sugars are useful indicators for the accumulation of microbial residues. A 14-day incubation experiment with C4 and C3 sucrose additions was carried out to investigate the relationships between amino sugar-specific shifts in δ13C values and those of CO2 production, microbial biomass C, K2SO4 extractable C and soil organic C (SOC). High performance anion exchange chromatography (HPAEC-IRMS) was able to measure amino-sugar specific δ13C values for muramic acid (MurN), galactosamine (GalN), and glucosamine (GlcN) in the range of natural abundance. At day 7, the initial application of C4 sucrose significantly increased the δ13C value of MurN by 1.0‰ in comparison with the non-amended control treatment, whereas that of GalN and GlcN remained unchanged. This significant increase had disappeared by day 14. This means that the HPAEC-IRMS method is not useful for short-term incubation experiments in the natural abundance range, as the pool size, especially of GalN and GlcN, was too large for a significant response in δ13C values. The δ13C values significantly decreased in the order MurN (−23.2‰) > GalN (−25.7‰) > GlcN (−26.5‰) in the control treatment. Similar δ13C values were measured in GlcN, microbial biomass C, and SOC. MurN exhibited δ13C values similar to the K2SO4 extractable fraction. These results may be caused by differences in the access of bacteria and fungi to different SOC fractions or differences in metabolic fractionation in bacteria and fungi. C3 sucrose application without further nutrient supply seven days after C4 sucrose application together with N and P led to strong mineralization of freshly formed microbial residues.  相似文献   

12.
Phosphorus (P) tracing in natural environments is challenging, lacking stable P isotopes Oxygen isotope ratios in phosphate (δ18OP) represent a novel tool for tracing the biological cycling of P from the global scale down to hotspots at the micro‐scale and within particular soil compartments such as aggregates or pores. Despite the small number of studies available so far, existing data indicate that δ18OP values point to where, at what extent and how efficiently P is recycled in soils.  相似文献   

13.
Abstract

A study was carried out to compare the difference or N-yield method with the 15N natural abundance method for the estimation of the fractional contribution of biological N2 fixation in the different plant parts of nodulating and non-nodulating isolines of soybeans. The results indicated that the δ15N values of most plant parts of soybeans were significantly lower (p<0.05) in the nodulating than in the non-nodulating isoline. However, in the case of the root+nodule component, the δ15N value was higher in the nodulating than in the non-nodulating isoline possibly due to isotopic discrimination of 15N over 14N which may have occurred in the nodules. Inoculation of soybeans with the Bradyrhizobium japonicum strain CB 1809 increased significantly (p<0.05) the δ15N value of the root+nodule component implying that the effectiveness of the soybean-rhizobium symbiosis had increased by inoculation.

Percentage of plant N derived from atmospheric N2 fixation (%Ndfa) estimated by the 15N natural abundance method was highly correlated (r=0.762, p<0.01) with that by the difference or N-yield method and the differences between the two methods were not statistically significant. The agreement between the two methods was closer at maturity than at the early reproductive stage.

The %Ndfa obtained by the difference method ranged from 48.4 to 92.6% whereas the %Ndfa obtained by the 15N natural abundance method ranged from 43.2 to 92.4% in the different plant parts. Based on the 15N natural abundance method, approximately 15% of the N in pod, shoot, grain, and shell was derived from the soil but in the case of stover, this fraction was about 55%.  相似文献   

14.
The present study determined the influence of initial moisture conditions on the production and consumption of nitrous oxide (N2O) during denitrification and on the isotopic fingerprint of soil-emitted N2O. Sieved arable soil was pre-incubated at two different moisture contents: pre-wet at 75% and pre-dry at 20% water-filled pore space. After wetting to 90% water-filled pore space the soils were amended with glucose (400 kg C ha−1) and KNO3 (80 kg N ha−1) and incubated for 10 days under a He/O2-atmosphere. Antecedent moisture conditions affected denitrification. N2 + N2O fluxes and the N2O-to-N2 ratio were higher in soils which were pre-incubated under dry conditions, probably because mobilization of organic C during the pre-treatment enhanced denitrification. Gaseous N fluxes showed similar time patterns of production and reduction of N2O in both treatments, where N2O fluxes were initially increasing and maximised 3-4 days after fertilizer application, and N2 fluxes were delayed by 1-2 days. Time courses of δ15Nbulk-N2O and δ18O-N2O exhibited in both treatments increasing trends until maximum N2 fluxes occurred, reflecting isotope fractionation during intense NO3− reduction. Later this trend slowed down in the pre-dry treatment, while δ18O-N2O was constant and δ15Nbulk-N2O decreased in the pre-wet treatment. We explain these time patterns by non-homogenous distribution of NO3− and denitrification activity, resulting from application of NO3− and glucose to the surface of the soil. We assume that several process zones were thus created, which affected differently the isotopic signature of N2O and the N2O and N2 fluxes during the different stages of the process. We modelled the δ15Nbulk-N2O using process rates and associated fractionation factors for the pre-treated soils, which confirmed our hypothesis. The site preference (SP) initially decreased while N2O reduction was absent, which we could not explain by the N-flux pattern. During the subsequent increase in N2 flux, SP and δ18O-N2O increased concurrently, confirming that this isotope pattern is indicative for N2O reduction to N2. The possible effect of the antecedent moisture conditions of the soil on N2O emissions was shown to be important.  相似文献   

15.
The 15N natural abundance in Pinus densiflora Sieb. et Zucco that had been inoculated and not inoculated with ectomycorrhizal fungi (Suillus granulatus (L.:Fr.) O. Kuntze) was compared. The inoculated pine needles showed a lower δ15N value, while the uninoculated ones showed a higher δ15N value. Higher δ15N values in the mycelial mat of the ectomycorrhizal fungi compared to those of the inoculated pine needles were also observed. These facts indicate that nitrogen isotope fractionation occurred during the nitrogen transport from mycorrhizal fungi to the host plants.  相似文献   

16.
Abstract

The isotopic composition of water extracted from various parts of alfalfa (Medicago saliva) plants was compared with that transpired by the plants to validate water extraction procedures, and to define the degree of alteration of the isotopic composition of water that occurred in different plant parts. The mean δ2H and δ18O values of water extracted from the upper tap root and lower crown regions were < 1‰ and 0.3‰ different from that of water transpired, respectively, with an analytical precision similar to that found in previous studies on soils and trees. Water from other plant parts closer to the leaves was enriched in 2H (up to 12.6 in upper stems) and 18O (4.2‰) with respect to that transpired. The enrichment was associated with a greater variability in δ2H values between replicate plants. δ2H‐δ18O data indicated that the isotopic enrichment was due to evaporation during transpiration. The study showed that azeotropic distillation is an accurate means of extracting water from alfalfa, although care is required when obtaining plant samples for comparison with water from the root‐zone.  相似文献   

17.
Soil carbon dioxide (CO2) efflux is an important component of the carbon (C) cycle but the biological and physical processes involved in soil CO2 production and transport are not fully understood. To improve our knowledge, we present a new approach to measure simultaneously soil CO2 concentrations and efflux, and their respective isotopic signatures (δ13C‐CO2). To quantify soil air 13CO2 and 12CO2 concentrations, we adapted a method based on CO2 diffusion from soil pores into tubes with a highly gas‐permeable membrane wall. These tubes were placed horizontally at different depths in the soil. Air was sampled automatically from the tubes and injected through a diluting system into a tuneable diode laser absorption spectrometer. The CO2 and δ13C‐CO2 vertical profiles were thus obtained at hourly intervals. Our tests demonstrated the absence of fractionation in the membrane tubes for δ13C‐CO2. Subsequently, we set up field experiments for two forest soils, which showed that natural soil CO2 concentrations and δ13C‐CO2 were not affected significantly by the measurement system. While δ13C‐CO2 in air‐filled pores below 5 cm was constant over 3 days, we observed large diurnal variations in δ13C‐CO2 efflux. However, the average difference between the two measurements was close to ?4.4‰, which supports steady‐state diffusion over this 3‐day period. This new method seems to be a very effective way to measure the δ13C‐CO2 profile of the soil atmosphere, and demonstrates that the fractionation that occurs during diffusion is the main transport process that affects the δ13C‐CO2 of the soil CO2 efflux on a daily timescale while advection may account for within‐day variations.  相似文献   

18.
Nitrous oxide (N2O) is a greenhouse gas that is destroying the stratospheric ozone to an increasing degree. Because of nitrogenous fertilizer application, agricultural soil is an important contributor of global N2O. In Japan, tea fields are amended with the highest level of N fertilizers among agricultural soils, causing soil acidification and large N2O flux. In soil, microbes play key roles in producing and consuming N2O. A previous study investigated net N2O production in tea fields using N2O flux measurement and soil incubation, which are indirect methods to analyze relevant processes of N2O production and consumption in soil. In the present study, to analyze N2O concentrations and isotopomer ratios (bulk nitrogen and oxygen isotope ratios, δ15Nbulk and δ18O, and intramolecular 15N site preference, SP) and to reveal most probable microbial production processes and consumption (N2O reduction to N2) process of N2O, soil gas was collected from a tea field (pH 3.1–4.5) at 10–50 cm depths using a silicone tube. The combination of fertilization, precipitation, and temperature rise produced significantly high N2O concentrations. During the period of high N2O concentration (above 5.7 ppmv), SP, the difference in 15N/14N ratio between central (α) and terminal (β) nitrogen position in the linear N2O molecule (βNαNO) showed low values of 1.4‰–9.8‰, suggesting that the contribution of bacterial denitrification (nitrifier-denitrification and bacterial denitrifier-denitrification) was greater than that of bacterial nitrification or fungal denitrification. High SP values of 15.0‰–20.1‰ obtained at 10, 35, and 50 cm depths on 31 May 2011 (after one of fertilizations) during which soil temperatures were 15.8 °C–17.9 °C and water-filled pore space (WFPS) was 0.73–0.89 suggest that fungal denitrification and bacterial nitrification contributed to N2O production to a degree equivalent to that of bacterial denitrification.  相似文献   

19.
The distribution and natural abundance isotopic (δ15N) content of whole tissue and individual amino acids in plants in a temperate grassland were determined using ion chromatography (IC), continuous flow‐isotope ratio mass spectrometry (CF‐IRMS), and gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS). The results showed that the selected plants (Lolium perenne, Juncus effusus, and Brachythecium rutabulum) differed in their amino acid content and distribution from the parent grassland soil. Bulk and individual amino acid δ15N isotope signatures were different between the plants, which concurred with their functional strategy in relation to the relative acquisition of available N sources. The individual amino acid δ15N values of histidine and phenylalanine could be used to differentiate between the three plant species.  相似文献   

20.
There is an increasing demand to develop a means to trace phosphorus (P) movement through the environment as excessive inputs of P have led to the eutrophication of many fresh water bodies. 18O labeled phosphate has been suggested as a potential tool for tracing P, and other researchers are using information from natural abundance 18O levels of phosphate to study phosphorus cycling. The objective of this research was to determine the rate of biological de-labeling of 18O in soils. This objective was achieved using a laboratory incubation study in which three silt-loam textured soils were incubated with 250 mg kg−1 P18O4-P for a period of 3, 10, 30, or 50 d. The incubations were conducted on both sterilized and unsterilized soils. Following incubation, phosphate from soils was extracted with a modified Bray extractant and analyzed using electrospray ionization mass spectrometry to determine the distribution of labeled phosphate species. The half-life of P18O4 in the non-sterile soils ranged from 15 to 22 d, while there was no observed P18O4 de-labeling in sterile soils after 50 d. A parameterized numerical model was developed which provided insight into the dynamics of the individual labeled phosphate species, including their half-lives and relative concentrations across the incubation period. The use of P18O4 may be useful in areas where use of radioisotopes of P is restricted, and P18O4 has potential to be useful to elucidate the dynamics of the P cycle in soils.  相似文献   

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