257 research outputs found
Metabolic pathways of Amino Acids, Monosaccharides and Organic Acids in Soils assessed by Position-Specific Labeling
No full textMetabolic pathways of Amino Acids, Monosaccharides and Organic Acids in Soils assessed by Position-Specific Labeling
No full textMicrobial carbon recycling: an underestimated process controlling soil carbon dynamics – Part 2: A C<sub>3</sub>-C<sub>4</sub> vegetation change field labelling experiment
No full textThe mean residence times (MRT) of different compound classes of soil organic
matter (SOM) do not match their inherent recalcitrance to decomposition. One
reason for this is the stabilization within the soil matrix, but recycling,
i.e. the reuse of "old" organic material to form new biomass may also play
a role as it uncouples the residence times of organic matter from the
lifetime of discrete molecules in soil.
We analysed soil sugar dynamics in a natural 30-year old labelling
experiment after a wheat-maize vegetation change to determine the extent of
recycling and stabilization by assessing differences in turnover dynamics
between plant and microbial-derived sugars: while plant-derived sugars are
only affected by stabilization processes, microbial sugars may be subject to
both, stabilization and recycling. To disentangle the dynamics of soil
sugars, we separated different density fractions (free particulate organic
matter (fPOM), light occluded particulate organic matter (≤ 1.6 g cm−3; oPOM1.6), dense occluded particulate organic matter
(≤ 2 g cm−3; oPOM2) and mineral-associated organic matter (> 2 g cm−3; mineral)) of a silty loam under long-term wheat and maize
cultivation. The isotopic signature of neutral sugars was measured by high
pressure liquid chromatography coupled to isotope ratio mass spectrometry
(HPLC/IRMS), after hydrolysis with 4 M Trifluoroacetic acid.
While apparent MRT of sugars were comparable to total
organic carbon in the bulk soil and mineral fraction, the apparent MRT of
sugar carbon in the oPOM fractions were considerably lower than those of the
total carbon of these fractions. This indicates that oPOM formation was
fuelled by microbial activity feeding on new plant input. In the bulk soil,
MRT of the mainly plant-derived xylose were significantly lower than those
of mainly microbial-derived sugars like galactose, rhamnose, fucose,
indicating that recycling of organic matter is an important factor
regulating organic matter dynamics in soil
Microbial Metabolic Flux Analysis Using Position-Specific 13C-Labelled Glucose and Fragment 13C Analysis of Plfa
No full textMicrobial carbon recycling – an underestimated process controlling soil carbon dynamics – Part 1: A long-term laboratory incubation experiment
No full textIndependent of its chemical structure carbon (C) persists in soil for
several decades, controlled by stabilization and recycling. To disentangle
the importance of the two factors on the turnover dynamics of soil sugars,
an important compound of soil organic matter (SOM), a 3-year incubation
experiment was conducted on a silty loam soil under different types of land
use (arable land, grassland and forest) by adding 13C-labelled glucose.
The compound-specific isotope analysis of soil sugars was used to examine
the dynamics of different sugars during incubation.
Sugar dynamics were dominated by a pool of high mean residence times (MRT)
indicating that recycling plays an important role for sugars. However, this
was not substantially affected by soil C content. Six months after label
addition the contribution of the label was much higher for microbial biomass
than for CO2 production for all examined land use types, corroborating
that substrate recycling was very effective within the microbial biomass.
Two different patterns of tracer dynamics could be identified for different
sugars: while fucose and mannose showed highest label contribution at the
beginning of the incubation with a subsequent slow decline, galactose and
rhamnose were characterized by slow label incorporation with subsequently
constant levels, which indicates that recycling is dominating the dynamics
of these sugars. This may correspond to (a) different microbial growing
strategies (r and K-strategist) or (b) location within or outside the cell
membrane (lipopolysaccharides vs. exopolysaccharides) and thus be subject of
different re-use within the microbial food web. Our results show how the
microbial community recycles substrate very effectively and that high losses
of substrate only occur during initial stages after substrate addition. This
study indicates that recycling is one of the major processes explaining the
high MRT observed for many SOM fractions and thus is crucial for
understanding the global soil C cycle
Positive intercropping effects on biomass production are species-specific and involve rhizosphere enzyme activities: Evidence from a field study
No full text<jats:title>Abstract</jats:title><jats:p>Less attention has been given to soil enzymes that contribute to beneficial rhizosphere interactions in intercropping systems. Therefore, we performed a field experiment by growing faba bean, lupine, and maize in mono and mixed cultures in a moderately fertile soil. We measured shoot biomass and the kinetic parameters (maximal velocity (<jats:italic>V</jats:italic><jats:sub>max</jats:sub>) and Michaelis-constant (<jats:italic>K</jats:italic><jats:sub><jats:italic>m</jats:italic></jats:sub>)) of three key enzymes in the rhizosphere: Leucine-aminopeptidase (LAP), β-1,4-N-acetylglucosaminidase (NAG), and phosphomonoesterase (PHO). Faba bean benefitted in mixed cultures by greater shoot biomass production with both maize and lupine compared to its expected biomass in monoculture. Next, LAP and NAG kinetic parameters were less responsive to mono and mixed cultures across the crop species. In contrast, both the <jats:italic>V</jats:italic><jats:sub>max</jats:sub> and <jats:italic>K</jats:italic><jats:sub><jats:italic>m</jats:italic></jats:sub> values of PHO increased in the faba bean rhizosphere when grown in mixed cultures with maize and lupine. A positive relative interaction index for shoot P and N uptake for faba bean showed its net facilitative interactions in the mixed cultures. Overall, these results suggest that over-productivity in intercropping is crop-specific and the positive intercropping effects could be modulated by P availability. We argue that the enzyme activities involved in nutrient cycling should be incorporated in further research.</jats:p>
Soil organic matter origin and composition along a 3200 m elevation gradient on Mount Kilimanjaro
No full textBiochemistry of hexose and pentose transformations in soil analyzed by position-specific labeling and 13C-PLFA
No full text© 2014 Elsevier Ltd. Microbial transformations are key processes of soil organic matter (SOM) formation, stabilization and decomposition. Combination of position-specific 13C labeling with compound-specific 13C-PLFA analysis is a novel tool to trace metabolic pathways. This combination was used to analyze short-term transformations (3 and 10 days after tracer application) of two key monosaccharides: glucose and ribose in soil under field conditions. Transformations of sugars were quantified by the incorporation of 13C from individual molecule positions in bulk soil, microbial biomass (by CFE) and in cell membranes of microbial groups classified by 13C-PLFA.The 13C incorporation in the Gram negative bacteria was higher by one order of magnitude compared to all other microbial groups. All of the 13C recovered in soil on day 3 was allocated in microbial biomass. On day 10 however, a part of the 13C was recovered in non-extractable microbial cell components or microbial excretions. As sugars are not absorbed by mineral particles due to a lack of charged functional groups, their quick mineralization from soil solution is generally expected. However, microorganisms transformed sugars to metabolites with a slower turnover. The 13C incorporation from the individual glucose positions into soil and microbial biomass showed that the two main glucose utilizing pathways in organisms - glycolysis and the pentose phosphate pathway - exist in soils in parallel. However, the pattern of 13C incorporation from individual glucose positions into PLFAs showed intensive recycling of the added 13C via gluconeogenesis and a mixing of both glucose utilizing pathways. The pattern of position-specific incorporation of ribose C also shows initial utilization in the pentose phosphate pathway but is overprinted on day 10, again due to intensive recycling and mixing. This shows that glucose and ribose - as ubiquitous substrates - are used in various metabolic pathways and their C is intensively recycled in microbial biomass.Analyzing the fate of individual C atoms by position-specific labeling deeply improves our understanding of the pathways of microbial utilization of sugars (and other compounds) by microbial groups and so, of soil C fluxes
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
Die Rolle des Schreibens in Angeboten der beruflichen Qualifizierung. Methodisches Vorgehen und ausgewählte Ergebnisse des Verbundprojektes SpraSiBeQ
No full textBirnbaum T, Dippold-Schenk K, Hirsch D, Kupke J, Seyfarth M, Wernicke A. Die Rolle des Schreibens in Angeboten der beruflichen Qualifizierung. Methodisches Vorgehen und ausgewählte Ergebnisse des Verbundprojektes SpraSiBeQ. In: Siemon J, Ziegler B, Kimmelmann N, Tenberg R, eds. Beruf und Sprache - Anforderungen, Kompetenzen und Förderung. Zeitschrift für Berufs- und Wirtschaftspädagogik. Beiheft. Vol 28. Stuttgart: Franz Steiner Verlag; 2016: 101-121
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