460 research outputs found
Greenhouse estimates of CO2 and N2O emissions following surface application of grass mulch: importance of indigenous microflora of mulch
No full textThe effects of surface-applied, fresh grass mulch on CO2 and N2O emissions were determined for 7 weeks in a greenhouse microcosm study under aerated conditions with daily irrigation (1.8 mm day(-1)). Dynamics Of CO2 and N2O emissions were determined by automated, continuous flux measurements. Grass mulch was added (C input: 100 g C m(-2), N input: 9.2 g N m(-2)) to Soil columns (Ap horizon of a cambisol) and quartz sand columns to assess the importance of indigenous microflora of grass residues for mulch decomposition and N2O production. About 76% of the grass mulch carbon was respired within 50 days, regardless of whether the grass mulch was added to soil or quartz sand. Total N2O-N emissions caused by the surface application of grass mulch was equivalent to 0.3% (application on soil) and 0.2% (application on quartz sand) of the N applied in the grass mulch. As much as 89% of the diurnal variability in NO emission and 80% of the diurnal variability in CO2 release from the decomposing grass mulch could be explained by changes in the temperature. The results show that indigenous microflora present on the plant residues determine both the decomposition rate of the surface-applied grass mulch and N-mineralisation and denitrification of mulch N. (C) 2002 Elsevier Science Ltd. All rights reserved
Short-term effects of earthworm activity and straw amendment on the microbial C and N turnover in a remoistened arable soil after summer drought
No full textShort-term effects of actively burrowing Octolasion lacteum (ORL.) (Lumbricidae) on the microbial C and N turnover in an arable soil with a high clay content were studied in a microcosm experiment throughout a 16 day incubation. Treatments with or without amendment of winter wheat straw were compared under conditions of a moistening period after summer drought. The use of C-14 labeled straw allowed for analyzing the microbial use of different C components. Microbial biomass C, biomass N and ergosterol were only slightly affected by rewetting and not by O. lacteum in both cases. Increased values of soil microbial biomass were determined in the straw treatments even after 24 h of incubation. This extra biomass corresponded to the initial microbial colonization of the added straw. O. lacteum significantly increased CO2 production from soil organic matter and from the C-14-labeled straw. Higher release rates of C-14-CO2 were recorded shortly after insertion of earthworms. This effect remained until the end of the experiment. O. lacteum enhanced N mineralization. Earthworms significantly increased both mineral N content of soil and N leaching in the treatments without straw addition. Moreover, earthworms slightly reduced N immobilization in the treatments with straw addition. The immediate increase in microbial activity suggests that perturbation of soil is more important than substrate consumption for the effect of earthworms on C and N turnover in moistening periods after drought. (C) 2001 Elsevier Science Ltd. All rights reserved
Structural investigations on Xe/Pd(111) with spin-polarized LEED
No full textHilgers G, Potthoff M, Müller N, Heinzmann U. Structural investigations on Xe/Pd(111) with spin-polarized LEED. Surface Science. 1993;287-288(1):414-417
Microbial use of N-15-labelled maize residues affected by winter temperature scenarios
No full textA 56-day incubation experiment was carried out to investigate decomposition and microbial use of N-15-labelled maize (Zea mays L.) residues incubated under four winter temperature scenarios. The residues were mixed to mesocosms equivalent to 1.2 mg C and 42.5 mu g N g(-1) dry soil, after which the samples were incubated at a constant temperature of +4 degrees C, a constant -3 degrees C, and under multiple and single freeze thaw conditions. A constant +4 degrees C was most favourable for microbial substrate use, with 4- and 6-fold higher total and maize-C mineralization, respectively, in comparison with constant frost. The cumulative maize mineralization was not determined by the frequency of freeze thaw events, but regulated by the overall time of frost and thaw conditions. The decomposition of maize straw significantly increased soil organic C mineralization (in all scenarios) and incorporation into microbial biomass (in the freeze thaw scenarios only). The positive priming effects observed were equivalent to an additional loss of total soil organic C of between about 0.2 (continuous frost) and 0.8% (single freeze thaw). Microbial biomass was significantly increased after maize straw amendment, with constant frost and freeze thaw scenarios not having any negative effect on microbial biomass C compared with constant +4 degrees C. Highest fungal biomass was found after constant frost without fresh substrates and also after extended frost followed by a warm period when fresh plant residues were present. On average, 50% of the added maize N were recovered in the soil total N after 56 days of constant 4 degrees C and in the freeze thaw scenarios, with the strongest effect after single freezing and thawing. (C) 2013 Elsevier Ltd. All rights reserved.University of Kasse
Below and aboveground responses to lupines and litter mulch in a California grassland restored with native bunchgrasses
No full textGoals of ecosystem restoration in California grasslands include the reestablishment of plant communities with a high proportion of native species, and simultaneously improve soil nutrient cycling. Addition of annual lupines and a litter mulch layer were hypothesized to be factors that would promote the growth of the native perennial bunchgrass. Nassella pulchra, in a restored California grassland. To test this hypothesis, field mesocosms were installed, each encircling a Nassella plant, at a perennial grassland restoration site in Carmel Valley, California. Two sets of treatments were imposed: (I) seeding of the annual N-fixing legume, Lupinus bicolor; and (2) exchanging the grassland litter for a thicker mulch layer of C(4) grass litter (C/N = 99). Stable isotope analysis allowed the tracking of fates of N fixed by the legume and the C(4)-litter derived C. Treatments continued for 28 months, from December 2002 to April 2005, when most of the destructive measurements were taken. In 2005, neither treatment had significantly increased the biomass of the annuals or the perennial bunchgrass, and there was little effect on total soil C and N. Lupinus decreased the delta(15)N content, but did not affect the biomass, N and P content of the litter, which was largely composed of annual plants from the previous year. Lupinus resulted in higher soil microbial biomass carbon (SMB-C), and distinct effects on soil microbial communities, especially soil fungi, as measured by phospholipid fatty acid analysis (PLFA) and ergosterol. The high C/N litter mulch tended to increase biomass of Nassella, despite its lower P concentration, and it reduced SMB-C, presumably due to lower decomposition rates compared to the ambient litter. Using a high C/N litter mulch thus is ambiguous for grassland restoration. Repeated increases of legumes over a longer time frame may potentially increase soil fertility and soil C pools in California grasslands, but this study suggests that native perennial grasses may be slow to benefit. (C) 2009 Elsevier B.V. All rights reserved
Intravenous luteinizing hormone-releasing hormone has no effect on serum N-terminal pro-brain natriuretic peptide in children and adolescents
No full textBackground : Little is known about the acute effects of i.v. luteinizing hormone-releasing hormone (LHRH) on the heart function, therefore the aim of the present study was to measure N-terminal pro-brain natriuretic peptide (N-BNP) in children, who underwent a diagnostic work up for short stature or delayed puberty. Methods : N-BNP was measured in 52 children before and after administration of LHRH. Serum N-BNP obtained from 255 healthy children and adolescents (aged birth-18.3 years) served as a reference. Results : There was no significant difference between baseline N-BNP of children who underwent the LHRH diagnostic test and their healthy peers. There was no significant serum N-BNP level change before or after administration of LHRH (59 +/- 36 pg/mL vs 58 +/- 34 pg/mL). N-BNP fell from 399 +/- 425 pg/mL in newborns and reached 44 +/- 36 pg/mL in children aged 12-18 years. Conclusion : Short stature or delayed puberty had no effect on heart function determined by serum N-BNP; i.v. LHRH does not acutely influence the level of serum N-BNP
Effect of litter quality and soil fungi on macroaggregate dynamics and associated partitioning of litter carbon and nitrogen
No full textWe investigated the effect of plant residue decomposability and fungal biomass on the dynamics of macroaggregate (250-2000 mu m) formation in a three months' incubation experiment and determined the distribution of residue-derived C and N in the microbial biomass and in aggregate size fractions (250-2000 mu m, 53-250 mu m and <53 mu m) using (13)C and (15)N data. A silty loam soil (sieved <250 mu m) was incubated with and without addition of (15)N labelled maize leaves (C/N = 27.4) and roots (C/N = 86.4). Each treatment was carried out with and without fungicide application. The addition of maize residues enhanced soil respiration and microbial biomass C and N and resulted in increased macroaggregate formation with a higher and more rapid maximum macroaggregation in the soil amended with maize leaves than in that with addition of roots. Fungicide application led to a significant decline of microbial biomass C and mineralization of the added residues compared to untreated soils, which demonstrates a successful suppression of part of the active microbial biomass by the fungicide. However, this was not confirmed by a generally lower ergosterol concentration. Consequently, ergosterol was no reliable fungal biomarker in periods of rapid decline of the fungal biomass. A single addition of fungicide was insufficient for continued inhibition of the fungal biomass. Yet, a significant delay (28-42 days) in macroaggregation in fungicide treated compared to untreated samples highlighted the importance of the fungal biomass in macroaggregate formation. Macroaggregates were enriched in maize-derived (13)C and (15)N compared to microaggregates or the fraction <53 mu m. They turned over rapidly with decreasing substrate availability, which entailed a transfer of maize-derived C and N stored within macroaggregates during the first weeks of incubation to microaggregates with proceeding incubation time. Our results indicate that this transfer happened within macroaggregates, because no considerable amount of free particulate organic matter (POM) was released upon macroaggregate breakdown. We conclude that substrate decomposability and fungal activity are key factors determining extent and dynamics of macroaggregation during decomposition processes. Macroaggregate formation implied rapid incorporation and thereby short-term protection of maize-derived C and N. Moreover, macroaggregates allowed a transfer of maize-derived organic matter into microaggregates within macroaggregates, which prevented the release of significant amounts of free POM upon macroaggregate breakdown. Consequently, macroaggregates constitute to the transfer of recently added C into more stable soil organic matter fractions. (C) 2008 Elsevier Ltd. All rights reserved
Carbon and nitrogen mineralization after maize harvest between and within maize rows: a microcosm study using C-13 natural abundance
No full textThe sequestration of carbon in soil is not completely understood, and quantitative information about the rates of soil organic carbon (SOC) turnover could improve understanding. We analyzed the effects of the uneven distribution of crop residues after harvest of silage maize on C and N losses (CO2-C, dissolved organic carbon (DOC) and nitrogen (DON), and NO3-) from a Haplic Phaeozem and on the occurrence of priming effects induced by the decomposition of accumulated maize residues. Soil columns were taken from a continuous maize (since 1961) field after harvest i) between maize stalk rows M-bare) ii) within the maize rows including a standing maize stalk (M-stalk), and iii) from a continuous rye (since 1878) field after tillage (rye stalk and roots were mixed into the Ap horizon). The soil columns were incubated for 230 days at 8 degreesC with an irrigation rate of 2mm 10(-2) M CaCl2 per day. Natural C-13 abundance was used to distinguish between maize-derived C (in SOC and maize residues) and older C originating from former C-3 vegetation
The determination of delta C-13 in soil microbial biomass using fumigation-extraction
No full textThe determination of the isotopic composition of the microbial biomass C in soil is an important tool to study soil microbial ecology and the decomposition and microbial immobilization of soil organic C. We discuss advantages and disadvantages of different methods to determine C-13/C-12 in soil microbial biomass and propose a new procedure that is based on the UV-catalyzed liquid oxidation of fumigated and non-fumigated soil extracts combined with trapping of the released CO2 in liquid nitrogen and subsequent determination of delta(13)CO(2)-C by a gas chromatograph connected with an isotope ratio mass spectrometer (IRMS). This method was evaluated using test solutions with known isotopic composition and soil extracts. Additionally, the method was compared with an off-line sample preparation technique combined with isotope analysis by a dual-inlet IRMS and an on-line analysis using an elemental analyser connected with an IRMS. All methods applied obtained comparable results and there were no significant differences between the delta(13)C values measured. The off-line preparation procedure had the highest precision but it was also the most labour-intensive. The choice of the most suitable method depends mainly on the number of samples that have to be analysed, the salt concentration of the extracts and the differences of delta(13)C that have to be detected. The application of this method with liquid oxidation and subsequent GC-IRMS analysis showed that microbial biomass C of a grassland soil was C-13-enriched by 2parts per thousand delta(13)C(PDB) compared with the total soil organic C. The addition of maize straw resulted in a rapid immobilization of maize C in the microbial biomass. (C) 2003 Elsevier Science Ltd. All fights reserved
Dynamics of maize (Zea mays L.) leaf straw mineralization as affected by the presence of soil and the availability of nitrogen
No full textAn incubation experiment was carried out with maize (Zea mays L.) leaf straw to analyze the effects of mixing the residues with soil and N amendment on the decomposition process. In order to distinguish between soil effects and nitrogen effects for both the phyllospheric microorganisms already present on the surface of maize straw and soil microorganisms the N amendment was applied in two different placements: directly to the straw or to the soil. The experiment was performed in dynamic, automated microcosms for 22 days at 15 &DEG; C with 7 treatments: (1) untreated soil, (2) non-amended maize leaf straw without soil, (3) N amended maize leaf straw without soil, (4) soil mixed with maize leaf straw, (5) N amended soil, (6) N amended soil mixed with maize leaf straw, and (7) soil mixed with N amended maize leaf straw. (NH4NO3)-N-15-N-15 (5 at %) was added. Gas emissions (CO2, (CO2)-C-13 and N2O) were continuously recorded throughout the experiment. Microbial biomass C, biomass N, ergosterol, δC-13 of soil organic C and of microbial biomass C as well as N-15 in soil total N, mineral N and microbial biomass N were determined in soil samples at the end of the incubation. The CO2 evolution rate showed a lag-phase of two days in the non-amended maize leaf straw treatment without soil, which was completely eliminated when mineral N was added. The addition of N generally increased the CO2 evolution rate during the initial stages of maize leaf straw decomposition, but not the cumulative CO2 production. The presence of soil caused roughly a 50% increase in cumulative CO2 production within 22 days in the maize straw treatments due to a slower decrease Of CO2 evolution after the initial activity peak. Since there are no limitations of water or N, we suggest that soil provides a microbial community ensuring an effective succession of straw decomposing microorganisms. In the treatments where maize and soil was mixed, 75% of microbial biomass C was derived from maize. We concluded that this high contribution of maize using microbiota indicates a strong influence of organisms of phyllospheric origin to the microbial community in the soil after plant residues enter the soil. © 2005 Elsevier Ltd. All rights reserved
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