1,721,311 research outputs found
Soil microbial carbon turnover decreases with increasing molecular size
No full textIt is well established that soil microorganisms play an important role in respiration of newly fixed plant carbon. Recent results show that they also contribute significantly to soil organic matter (SOM) formation. We hypothesized that different molecular size classes of compounds in soil microbial biomass (SMB) have variable turnover time and in consequence influence SOM formation differentially. Here we used natural differences in carbon stable isotope signatures (d13C values) after C3eC4 vegetation change to track newly fixed C4 plant carbon into SMB molecular size classes. SMB was obtained by chloroform fumigation extraction (SFE) and d13C values of its size classes were measured using size exclusion chromatography coupled online to liquid chromatography‒isotope ratio mass spectrometry (SECeLC eIRMS). Resolved SMB was assigned to 5 size classes of 1800e9800, 800e1800, 380e800, 180e380 and 50e180 Da respectively. The contribution of recent C4 plant carbon to size classes of SMB decreased with increasing molecular weight (MW). It ranged from 77 19% in the lowest MW size class size class to 41 14% in the highest MW size class in a sandy soil and from 59 18% in the lowest MW size class to 8 15% in the highest MW size class in a clayey soil. A decreasing carbon turnover of compounds in SMB extracts along a continuum of molecular size from small to large implies that low molecular weight microbial compounds are rapidly metabolized products that link to fast respiratory carbon fluxes, whereas high molecular weight ones could be products of microbial synthesis like structural compounds that have slower turnover rates and link to slower SOM formation. Our methods help avoid contamination of CFE extracts and the results help explain why SMB turnover is faster in CFE extracts when compared to calculations using membrane lipids (e.g. PLFA-based)
Overstory-specific effects of litter fall on the microbial carbon turnover in a mature deciduous forest
No full textMature deciduous forests can serve as important carbon (C) sinks, but the C storage differs significantly in dependency on the tree species. To specify the significance of overstory-specific effects of litter fall on the soil microbial C turnover, we have investigated the C-13 isotopic signature of microbial biomarker phospholipid fatty acids (PLFAs). Samples were taken under pure Fagus sylvatica and mixed overstory (F. sylvatica and Fraxinus excelsior or F. excelsior, Acer spp. and F. sylvatica) in a mature temperate deciduous forest in Central Germany 4 weeks prior to and 3 weeks after litter fall. Accordingly, the CO2 emission from soil was measured before, during and after the litter fall to investigate the response of decomposition. At all sites and at both sampling dates the fungal biomarker PLFA 18:2 omega 6,9 had predominantly lower delta C-13 values (from -32 to -43 parts per thousand) than the bacterial biomarker PLFAs (delta C-13 values from -23 to -39 parts per thousand). This difference indicated that fungi generally used preferentially plant derived C, whereas the bacterial populations include groups which used SOM derived C, independent on the overstory, trees. Under pure F. sylvatica overstory the delta C-13 values of microbial biomarker PLFAs were slightly decreased (up to 2 parts per thousand for 17:0br) or unchanged after litter fall. By contrast, under both variants of mixed overstory the delta C-13 values of biomarker PLFAs of fungi (18:2w6,9) were increased after litter fall (+3.5 and +3.8 parts per thousand). This might be explained partly by a faster initial decomposition of foliar litter from mixed overstory already during litter fall as confirmed by higher CO2 emission under mixed F. excelsior, Acer spp. and F. sylvatica than under pure F sylvatica in this period. However, the involved microbial populations differed overstory-specific. Bacterial biomarker PLFAs with strongest overstory-specific differences in the response on litter fall were 17:0br (Gram-positive bacteria), 18:1 and 19:0cy (Gram-negative bacteria). The present results indicate that a tree species conversion even exclusively between deciduous tree species might alter the soil microbial C turnover during litter decomposition and suggest that it would in the long-term change the SOM stability and C storage. (C) 2009 Elsevier B.V. All rights reserved. [References: 54
Above and below ground carbohydrate allocation differs between ash (Fraxinus excelsior L.) and beech (Fagus sylvatica L.).
Full text linkWe investigated soluble carbohydrate transport in trees that differed in their phloem loading strategies in order to better understand the transport of photosynthetic products into the roots and the rhizosphere as this knowledge is needed to better understand the respiratory processes in the rhizosphere. We compared beech, which is suggested to use mainly passive loading of transport sugars along a concentration gradient into the phloem, with ash that uses active loading and polymer trapping of raffinose family oligosaccharides (RFOs). We pulse-labeled 20 four-year old European beech and 20 four-year old ash trees with 13CO2 and tracked the fate of the label within different plant compartments. We extracted soluble carbohydrates from leaves, bark of stems and branches, and fine roots, measured their amount and isotopic content and calculated their turnover times. In beech one part of the sucrose was rapidly transported into sink tissues without major exchange with storage pools whereas another part of sucrose was strongly exchanged with unlabeled possibly stored sucrose. In contrast the storage and allocation patterns in ash depended on the identity of the transported sugars. RFO were the most important transport sugars that had highest turnover in all shoot compartments. However, the turnover of RFOs in the roots was uncoupled from the shoot. The only significant relation between sugars in the stem base and in the roots of ash was found for the amount (r2 = 0.50; p = 0.001) and isotopic content (r2 = 0.47; p = 0.01) of sucrose. The negative relation of the amounts suggested an active transport of sucrose into the roots of ash. Sucrose concentration in the root also best explained the concentration of RFOs in the roots suggesting that RFO in the roots of ash may be resynthesized from sucrose. Our results interestingly suggest that in both tree species only sucrose directly entered the fine root system and that in ash RFOs are transported indirectly into the fine roots only. The direct transport of sucrose might be passive in beech but active in ash (sustained active up- and unloading to co-cells), which would correspond to the phloem loading strategies. Our results give first hints that the transport of carbohydrates between shoot and root is not necessarily continuous and involves passive (beech) and active (ash) transport processes, which may be controlled by the phloem unloading
Bulk density from the Jena Experiment (Main Experiment, year 2006)
No full textThis data set contains measurements of soil bulk density in different depth layers. Data presented here is from the Main Experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained in general by bi-annual weeding and mowing. Since 2010, plot size was reduced to 5 x 6 m and plots were weeded three times per year.
Soil bulk density was determined in spring from undisturbed soil samples to a depth of 30 cm. Three soil cores per plot were taken with a split tube sampler with an inner diameter of 4.8 cm and separated in depth increments of five cm. The bulk material was passed through a sieve with 2 mm mesh size, dried to constant weight at 40 °C and subsequently weighed to calculate the density.
Paired sampling was chosen to avoid additional spatial variability (Lal et al., 2000), which means that three of the five sampling locations of 2002 bulk density measurement that were in the core area of the plots were chosen for the repeated sampling. The spatial distance of the paired soil samples were less than 30 cm
Effects of tree identity dominate over tree diversity on the soil microbial community structure
No full textThis study investigated the possible effects of tree species diversity and identity on the soil microbial community in a species-rich temperate broad-leaved forest. For the first time, we separated the effects of tree identity and tree species diversity on the link between above and belowground communities in a near-natural forest. We established 100 tree clusters consisting of each three tree individuals represented by beech (Fagus sylvatica L.), ash (Fraxinus excelsior L.), hornbeam (Carpinus betulus L.), maple (Acer pseudoplatanus L.), or lime (Tilia spec.) at two different sites in the Hainich National Park (Thuringia, Germany). The tree clusters included one, two or three species forming a diversity gradient. We investigated the microbial community structure, using phospholipid fatty acid (PLFA) profiles, in mineral soil samples (0–10 cm) collected in the centre of each cluster. The lowest total PLFA amounts were found in the pure beech clusters (79.0 ± 23.5 nmol g−1 soil dw), the highest PLFA amounts existed in the pure ash clusters (287.3 ± 211.3 nmol g−1 soil dw). Using principle components analyses (PCA) and redundancy analyses (RDA), we found only for the variables ‘relative proportion of beech trees’ and ‘living lime fine root tips associated with ectomycorrhiza’ a significant effect on the PLFA composition. The microbial community structure was mainly determined by abiotic environmental parameters such as soil pH or clay content. The different species richness levels in the clusters did not significantly differ in their total PLFA amounts and their PLFA composition. We observed a tendency that the PLFA profiles of the microbial communities in more tree species-rich clusters were less influenced by individual PLFAs (more homogenous) than those from species-poor clusters. We concluded that tree species identity and site conditions were more important factors determining the soil microbial community structure than tree species diversity per se
Bulk density from the Jena Experiment (Main Experiment, year 2004)
No full textThis data set contains measurements of soil bulk density in different depth layers. Data presented here is from the Main Experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained in general by bi-annual weeding and mowing. Since 2010, plot size was reduced to 5 x 6 m and plots were weeded three times per year.
Soil bulk density was determined in spring from undisturbed soil samples to a depth of 30 cm. Three soil cores per plot were taken with a split tube sampler with an inner diameter of 4.8 cm and separated in depth increments of five cm. The bulk material was passed through a sieve with 2 mm mesh size, dried to constant weight at 40 °C and subsequently weighed to calculate the density.
Paired sampling was chosen to avoid additional spatial variability (Lal et al., 2000), which means that three of the five sampling locations of 2002 bulk density measurement, that were in the core area of the plots, were chosen for the repeated sampling. The spatial distance of the paired soil samples were less than 30 cm
Temperate and Boreal Old-Growth Forests: How do Their Growth Dynamics and Biodiversity Differ from Young Stands and Managed Forests?
No full textUmsatz und Stabilisierung von organischem Kohlenstoff in Böden
Full text linkIm Rahmen der vorliegenden Arbeit sollte die Dynamik des Kohlenstoffumsatzes im Boden im Hinblick einer möglichen Stabilisierung von organischem Kohlenstoff untersucht werden. Besonderes Interesse galt dabei dem Umsatz molekularer Bestandteile der organischen Bodensubstanz sowie der Funktion der mikrobiellen Biomasse. Für diese Untersuchungen wurden Böden verwendet, die einem Vegetationswechsel von C3-Pflanzen mit δ13C = -27 ‰, zu C4-Pflanzen mit δ13C = -14 ‰ unterzogen wurden. Die Differenz der Isotopengehalte dieser Pflanzen von ca. 13 ‰ wird zur Markierung der organischen Bodensubstanz (OBS) genutzt, um zwischen neu eingetragenem, C4-bürtigen und bereits vorhandenem, C3-bürtigen Kohlenstoff unterscheiden zu können. Neben der Analyse des stabilen Kohlenstoffisotops 13C wurden auch Analysen am radioaktivenKohlenstoffisotop 14C durchgeführt, um die Stabilität organischer Bodensubstanz direkt zu bestimmen. Es zeigte sich, dass der Kohlenstoffumsatz im Boden primär von der Menge an eingetragenen Pflanzenrückständen in den Boden sowie von der verfügbaren Menge an Stickstoff abhängt. Der Umsatz des organischen Materials ist dabei umso höher, je höher die Menge an eingetragenem Pflanzenmaterial in den Boden ist. Deshalb nimmt die mittlere Verweilzeit organischer Substanzen im Boden mit steigendem Umsatz ab. Hohe mittlere Verweilzeiten der OBS von einigen hundert bis zu tausend Jahren deuten an, dass organischer Kohlenstoff über lange Zeit im Boden stabilisiert werden könnte
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