1,721,157 research outputs found
Isotope fractionation factors of N(2)O diffusion
No full textIsotopic signatures of N(2)O are increasingly used to constrain the total global flux and the relative contribution of nitrification and denitrification to N(2)O emissions. Interpretation of isotopic signatures of soil-emitted N(2)O can be complicated by the isotopic effects of gas diffusion. The aim of our study was to measure the isotopic fractionation factors of diffusion for the isotopologues of N(2)O and to estimate the potential effect of diffusive fractionation during N(2)O fluxes from soils using simple simulations. Diffusion experiments were conducted to monitor isotopic signatures of N(2)O im reservoirs that lost N(2)O by defined diffusive fluxes. Two different mathematical approaches were used to derive diffusive isotope fractionation factors for (18)O (epsilon(180)), average (15)N (epsilon(bulk)) and (15)N of the central (alpha-) and peripheral (beta-) position within the linear N(2)O molecule (epsilon(15N alpha,) epsilon(15N beta)). The measured r(180) was -7.79 +/- 0.27 parts per thousand and thus higher than the theoretical value of -8.7 parts per thousand. Conversely, the measured epsilon(bulk) (-5.23 +/- 0.27 parts per thousand) was lower than the theoretical value (-4.4 parts per thousand). The measured site-specific (15)N fractionation factors were not equal, giving a difference between epsilon(15N alpha) and epsilon(15N beta) (epsilon(SP)) of 1.55 +/- 0.28 parts per thousand. Diffusive fluxes of the N(2)O isotopologues from the soil pore space to the atmosphere were simulated, showing that isotopic signatures of N(2)O source pools and emitted N(2)O can be substantially different during periods of non-steady state fluxes. Our results show that diffusive isotope fractionation should be taken into account when interpreting natural abundance isotopic signatures of N(2)O fluxes from soils. Copyright (C) 2008 John Wiley & Sons, Ltd
Effects of beech (Fagus sylvatica), ash (Fraxinus excelsior) and lime (Tilia spec.) on soil chemical properties in a mixed deciduous forest
Full text linkAims We aimed to determine the influence of the distribution of different broadleaved tree species on soil chemical properties in a mature deciduous forest in Central Germany. Methods Triangles of three neighboring trees (tree clusters) that consisted of either one or two species of European beech (Fagus sylvatica L.), European ash (Fraxinus excelsior L.) or lime (Tilia cordata Mill. or Tilia platyphyllos Scop.) were selected and analyzed for their litterfall chemistry and chemical properties of the forest floor and mineral soil (0-10 cm and 10-20 cm). Results Base saturation, pH-value and the stock of exchangeable Mg2+ (0-10 cm) were highest under ash and lowest under beech. The proportion of exchangeable Al3+ was smallest under ash and highest under beech. The stock of exchangeable Mg2+ and Ca2+ correlated positively with the annual input of the respective nutrient from leaf litterfall. Ash leaf litterfall contained highest amounts of Mg and Ca. Beech leaf litterfall showed the highest C:N ratio and lignin: N ratio. Soil pH, stocks of organic C, total N and exchangeable Mg2+ and Ca2+ correlated positively with increasing proportions of ash leaf litter to total leaf litterfall. Conclusions Our results indicate that the abundance of ash in beech dominated forests on loess over limestone had a positive effect on soil chemical properties and reduced soil acidification. The intermixture and distribution of ash in beech-dominated stands resulted in an increase of the horizontal and vertical diversity of the soil habitat.Deutsche Forschungsgemeinschaft (DFG) [1086
Allocation and dynamics of C and N within plant-soil system of ash and beech
No full textForest management requires a profound understanding of how tree species affect C and N cycles in ecosystems. The large C and N stocks in forest soils complicate research on the effects of tree species on C and N pools. In-situ C-13 and N-15 labeling in undisturbed, natural forests enable not only tracing of C and N fluxes, but also reveal insight into the interactions at the plant-soil-atmosphere interface. In-situ dual C-13 and N-15 pulse labeling of 20 beeches (Fagus sylvatica L.) and 20 ashes (Fraxinus excelsior L.) allowed tracing the fate of assimilated C and N in trees and soils in an unmanaged forest system in the Hainich National Park (Germany). Leaf, stem, root, and soil samples as well as microbial biomass were analyzed to quantify the allocation of 13C and N-15 for 60 d after labeling and along spatial gradients in the soil with increasing distance from the stem. For trees of similar heights (approximate to 4 m), beech (20%) assimilated twice as much as ash (9%) of the applied (CO2)-C-13, but beech and ash incorporated similar N-15 amounts (45%) into leaves. The photosynthates were transported belowground through the phloem more rapidly in beech than in ash. Ash preferentially accumulated N-15 and C-13 in the roots. In contrast, beech released more of this initially assimilated C-13 (2.0% relative C-13 allocation) and N-15 (0.1% relative N-15 allocation) via rhizodeposition into the soil than ash (0.2% relative C-13, 0.04% relative N-15 allocation), which was also subsequently recovered in microbial biomass. These results on C and N partitioning contribute to an improved understanding of the effects of European beech and ash on the C and N cycles in deciduous broad-leaved forest. Differences in C and N allocation patterns between ash and beech are one mechanism of niche differentiation in forests containing both species.German Research Foundation (DFG); DFG Graduiertenkolleg 108
Isotopomer signatures of soil-emitted N2O under different moisture conditions - A microcosm study with arable loess soil
No full textSoils represent the major source of the atmospheric greenhouse gas nitrous oxide (N2O) and there is a need to better constrain the total global flux and the relative contribution of the microbial source processes. The aim of our study was to evaluate isotopomer analysis of N2O (intramolecular distribution of N-15) as well as conventional nitrogen and oxygen isotope ratios (i) as a tool to identify N2O production processes in soils and (ii) to constrain the isotopic fingerprint of soil-derived N2O. We conducted a microcosm study with arable loess soil fertilized with 20 mg N kg(-1) of (NO3-)-N-15-labeled or non-labeled ammonium nitrate. Soils were incubated for 16 d at varying moisture (55%, 75% and 85% water-filled pore space (WFPS)) in order to establish different levels of nitrification and denitrification. Dual isotope and isotopomer ratios of emitted N2O were determined by mass spectrometric analysis of delta O-18, average delta N-15 (delta N-15(bulk)) and N-15 site preference (SP = difference in delta N-15 between the central and peripheral N-positions of the asymmetric N2O molecule). Total rates and N2O emission of denitrification and nitrification were determined by N-15 analysis of headspace gases and soil extracts of the (NO3-)-N-15 treatment. N2O emission and denitrification increased with moisture whereas gross nitrification was almost constant. In the 55% WFPS treatment, more than half of the N2O flux was derived from nitrification, whereas denitrification was the dominant N2O source in the 75% WFPS and 85% WFPS treatments. Moisture conditions were reflected by the isotopic signatures since highly significant differences were observed for average delta N-15(bulk) SP and delta O-18. Experiment means of the 75% WFPS and 85% WFPS treatments gave negative delta N-15(bulk) (-18.0 parts per thousand and -34.8 parts per thousand, respectively) and positive SP (8.6 parts per thousand and 15.3 parts per thousand, respectively), which we explained by the fractionation during N2O production and partial reduction to N-2. In the 55% WFPS treatment, mean SP was relatively low (1.9 parts per thousand), which suggests that nitrification produced N2O with low or negative SP. The observed influence of process condition on isotopomer signatures suggests that the isotopomer approach might be suitable for identifying N2O source processes. However, more research is needed to determine the impact from process rates and microbial community structure. Isotopomer signatures were within the range reported from previous soil studies which supports the assumption that SP of soil-derived N2O is lower than SP of tropospheric N2O. (c) 2006 Elsevier Ltd. All rights reserved
L.) during the growth phase
No full textTo study the incorporation of carbon and nitrogen in different plant fractions, 3‐year‐old‐beech (Fagus sylvatica L.) seedlings were exposed in microcosms to a dual‐labelling experiment employing 13C and 15N throughout one season. Leaves, stems, coarse and fine roots were harvested 6, 12 and 18 weeks after bud break (June to September) and used to isolate acid‐detergent fibre lignins (ADF lignin) for the determination of carbon and nitrogen and their isotope ratios. Lignin concentrations were also determined with the thioglycolic acid method. The highest lignin concentrations were found in fine roots. ADF lignins of all tissues analysed, especially those of leaves, also contained significant concentrations of nitrogen. This suggests that lignin‐bound proteins constitute an important cell wall fraction and shows that the ADF method is not suitable to determine genuine lignin. ADF lignin should be re‐named as ligno‐protein fraction. Whole‐leaf biomass was composed of 50 to 70% newly assimilated carbon and about 7% newly assimilated nitrogen; net changes in the isotope ratios were not observed during the experimental period. In the other tissues analysed, the fraction of new carbon and nitrogen was initially low and increased significantly during the time‐course of the experiment, whereas the total tissue concentrations of carbon remained almost unaffected and nitrogen declined. At the end of the experiment, the whole‐tissue biomass and ADF lignins of fine roots contained about 65 and 50% new carbon and about 50 and 40% new nitrogen, respectively. These results indicate that significant metabolic activity was related to the formation of structural biopolymers after leaf growth, especially below‐ground and that this activity also led to a substantial binding of nitrogen to structural compounds
Translocation of C-13-labeled leaf or root litter carbon of beech (Fagus sylvatica L.) and ash (Fraxinus excelsior L.) during decomposition - A laboratory incubation experiment
No full textThe aim was to quantify medium term litter type and litter mixture effects on the translocation and transformation dynamics of root and leaf litter C during decomposition. Partitioning of C-13-labeled root or leaf litter C (beech - Fagus sylvatica L., ash - Fraxinus excelsior L.) to CO2, water-extractable organic C (WEOC), microbial biomass C (C-MB) and light (LF) and heavy soil fraction (HF) was determined in a laboratory decomposition experiment of 206 days. The proportions of C mineralized from ash leaf (34%) and root litter (29%) were higher than those from beech leaf (24%) and root litter (23%). In mixture with beech, the mineralization of ash leaf litter was enhanced. Mineralization was positively correlated with litter-derived WEOC until day 29. Water-extractable organic C declined with time, until <0.1% of litter C remained in this fraction. Litter-C recovery in C-MB was higher for ash (0.7-1.0%) than for beech (0.2-0.4%). The litter C recovery in HF (4-12%) was positively correlated with that in WEOC (days 9 and 29) and C-MB, but did not differ between treatments. Ash leaf litter mineralization showed different behavior in mixed treatments from pure treatments. Thus, the ability to transfer results from pure to mixed treatments is limited. The litter differed in chemical composition and in mineralization dynamics, but differences in partitioning to HF, WEOC and MB were finally of minor importance. (C) 2015 Elsevier Ltd. All rights reserved
Isotopologue ratios of N2O emitted from microcosms with NH4+ fertilized arable soils under conditions favoring nitrification
No full textSoils represent the major source of the atmospheric greenhouse gas nitrous oxide (N2O) and there is a need to better constrain the total global flux and the relative contribution of the microbial source processes. The aim of our study was to determine variability and control of the isotopic fingerprint of N2O fluxes following NH4+-fertilization and dominated by nitrification. We conducted a microcosm study with three arable soils fertilized with 0-140 mg NH4+-N kg(-1). Fractions of N2O derived from nitrification and denitrification were determined in parallel experiments using the N-15 tracer and acetylene inhibition techniques or by comparison with unfertilized treatments. Soils were incubated for 3-10 days at low moisture (30-55% water-filled pore space) in order to establish conditions favoring nitrification. Dual isotope and isotopomer ratios of emitted N2O were determined by mass spectrometric analysis of 6180, average delta N-15 (delta N-15 bulk) and N-15 site preference (SP = difference in delta N-15 between the central and peripheral N positions of the asymmetric N2O molecule). N2O originated mainly from nitrification (> 80%) in all treatments and the proportion of NH4+ nitrified that was lost as N2O ranged between 0.07 and 0.45%. delta O-18 and SP of N2O fluxes ranged from 15 to 28.4 parts per thousand and from 13.9 to 29.8 parts per thousand, respectively. These ranges overlapped with isotopic signatures of N2O from denitrification reported previously. There was a negative correlation between SP and delta O-18 which is opposite to reported trends in N2O from denitrification. Variation of average N-15 signatures of N2O (delta N-15(bulk)) did not supply process information, apparently because a strong shift in precursor signatures masked process-specific effects on delta N-15(bulk). Maximum SP of total N2O fluxes and of nitrification fluxes was close to reported SP of N2O from NH4+ or NH2OH conversion by autotrophic nitrifiers, suggesting that SP close to 30 parts per thousand is typical for autotrophic nitrification in soils following NH4+-fertilization. The results suggest that the delta O-18/SP fingerprint of N2O might be used as a new indicator of the dominant source process of N2O fluxes in soils. (C) 2008 Elsevier Ltd. All rights reserved.Deutsche Forschungsgemeinschaft (DFG
Decomposition of maize residues after manipulation of colonization and its contribution to the soil microbial biomass
No full textA 28-day incubation experiment at 12 degrees C was carried out on the decomposition of maize leaf litter to answer the questions: (1) Is the decomposition process altered by chemical manipulations due to differences in the colonization of maize leaf litter? (2) Do organisms using this maize material contribute significantly to the soil microbial biomass? The extraction of the maize straw reduced its initial microbial biomass C content by 25%. Fumigation and extraction eliminated the microbial biomass by 88%. In total, 17% of added maize straw C was mineralized to CO(2) during the 28-day incubation at 12 degrees C in the treatment with non-manipulated straw. Only 14% of added C was mineralized in the treatment with extracted straw as well as in the treatment with fumigated and extracted straw. The net increase in microbial biomass C was 79 mu g g(-1) soil in the treatment with non-manipulated straw and an insignificant 9 mu g g(-1) soil in the two treatments with manipulated straw. However, the net increase did not reflect the fact that the addition of maize straw replaced an identical 58% (approximate to 180 mu g g(-1) soil) of the autochthonous microbial biomass C(3)-C in all three straw treatments. In the two treatments with manipulated straw, the formation of maize-derived microbial biomass C(4)-C was significantly reduced by 25%. In the three straw treatments, the ratio of fungal ergosterol-to-microbial biomass C ratio showed a constant 60% increase compared to the control, and the contents of glucosamine and muramic acid increased by 18%. The average fungal C/bacterial C ratio was 3.6 in the soil and 5.0 in the recovered maize straw, indicating that fungal dominance was not altered by the initial chemical manipulations of the maize straw-colonizing microorganisms
Application of the DNDC model to predict N<sub>2</sub>O emissions from sandy arable soils with differing fertilization in a long-term experiment.
No full textModeling crop growth and soil N dynamics is difficult due to the complex nature of soil-plant systems. In several studies, the DNDC model has been claimed to be well-suited for this purpose whereas in other studies applications of the model were less successful. Objectives of this study were to test a calibration and validation scheme for DNDC-model applications to describe a field experiment with spring wheat on a sandy soil near Darmstadt (SW Germany) using different fertilizer types (either application of mineral fertilizer and straw-MSI; or application of farmyard manure-FYM) and rates (low-MSI(L), FYM(L); and medium-MSI(M), FYM(M)). The model test is based on a model parameterization to best describe the case MSI(L) and applies this parameterization for a retrospective simulation of the other cases (MSIM, FYML, FYMM) including crop growth and N(2)O emissions. Soil water contents were not accurately simulated using either the DNDC default values for a loamy sand or for the next finer texture class or using results from the pedotransfer function provided by ROSETTA. After successful calibration of the soil water flow model using a soil texture class that led to the best fit of the measured water content data, grain yield of spring wheat and cumulative N(2)O emission were slightly underestimated by DNDC and were between 91% and 86% of the measured data. A subsequent calibration of the yields and cumulative N(2)O emissions from soils of the MSIL treatment gave a good prediction of crop growth and N(2)O emissions in the MSIM treatment, but a marked underestimation of yields of the FYM treatments. Cumulative N(2)O emissions were predicted well for all MSI and FYM treatments, but seasonal dynamics were not. Overall, our results indicated that for the sandy soil in Germany, site-specific calibration was essentially required for the soil hydrology and that a calibration was useful for a subsequent prediction where greater amounts of the same fertilizer were used, but not useful for a prediction with a different fertilizer type
Effect of fertilization on respiration from different sources in a sandy soil of an agricultural long-term experiment
No full textAnnual changes in stocks of soil organic carbon may be detected by measurement of heterotrophic respiration, but field studies of heterotrophic respiration in long-term fertilization experiments on sandy soils are scarce. Our objectives were to: (1) investigate the influence of fertilizer type on mineralization of soil organic carbon and crop residue, and (2) show how fertilization treatments affect the annual C balance (net ecosystem carbon balance, NECB; negative values indicate a CO2-source) in the sandy soil of the Darmstadt experiment. Treatments were long-term mineral fertilization with cereal straw incorporation (MSI) and application of rotted farmyard manure (FYM), both treatments receiving 14 g N m(-2) year(-1). This study used delta C-13 natural abundance after introduction of a C-4 crop to distinguish between different sources of respiration. Mineralization derived from C-3 sources was similar for MSI and FYM treatments (similar to 270 g C m(-2) year(-1)). The rate of residue mineralization in MSI treatments was higher, resulting in a mineralization of 49 and 37% of initial residue C in the soil of MSI and FYM treatments, respectively. The NECB (g C m(-2) year(-1)) indicated the MSI treatment (approximately - 190) as a stronger source compared with the FYM treatment (similar to-30).Deutsche Forschungsgemeinschaft (DFG) [GRK 1397/1
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