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  • Forest Soils
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  • 1
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2017, Vol.180(2), pp.220-230
    Description: Standard procedures to assess P availability in soils are based on batch experiments with various extractants. However, in most soils P nutrition is less limited by bulk stocks but by strong adsorption and transport limitation. The basic principle of root‐phosphate uptake is to strip phosphate locally from the solid phase by forming a radial depletion zone in the soil solution, optionally enhanced by release of mobilizing substances. Microdialysis (MD), a well‐established method in pharmacokinetics, is capable to mimic important characteristics of P root uptake. The sampling is by diffusional exchange through a semipermeable membrane covering the probes with their sub‐mm tubular structure. Additionally, the direct environment of the probe can be chemically modified by adding, ., carboxylates to the perfusate. This study is the first approach to test the applicability of MD in assessing plant available phosphate in soils and to develop a framework for its appropriate use.We used MD in stirred solutions to quantify the effect of pumping rate, concomitant ions, and pH value on phosphate recovery. Furthermore, we measured phosphate yield of top‐soil material from a beech forest, a non‐fertilized grassland, and from a fertilized corn field. Three perfusates have been used based on a 1 mM KNO solution: pure (1), with 0.1 mM citric acid (2), and with 1 mM citric acid (3). Additionally, a radial diffusion model has been parametrized for the stirred solutions and the beech forest soil.Results from the tests in stirred solutions were in good agreement with reported observations obtained for other ionic species. This shows the principal suitability of the experimental setup for phosphate tests. We observed a significant dependency of phosphate uptake into the MD probes on dialysate pumping rate and on ionic strength of the outside solution. In the soils, we observed uptake rates of the probes between 1.5 × 10 and 6.7 × 10 mol s cm in case of no citrate addition. Surprisingly, median uptake rates were mostly independent of the bulk soil stocks, but the P‐fertilized soil revealed a strong tailing towards higher values. This indicates the occurrence of hot P spots in soils. Citrate addition increased P yields only in the higher concentration but not in the forest soil. The order of magnitude of MD uptake rates from the soil samples matched root‐length related uptake rates from other studies. The micro‐radial citrate release in MD reflects the processes controlling phosphate mobilization in the rhizosphere better than measurements based on “flooding” of soil samples with citric acid in batch experiments. Important challenges in MD with phosphate are small volumes of dialysate with extremely low concentrations and a high variability of results due to soil heterogeneity and between‐probe variability. We conclude that MD is a promising tool to complement existing P‐analytical procedures, especially when spatial aspects or the release of mobilizing substances are in focus.
    Keywords: Plant Availability ; Diffusion Limitation ; Spatial Heterogeneity ; Carboxylates
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 2
    Language: English
    In: Catena, April 2016, Vol.139, pp.9-18
    Description: Riparian woodlands consist of different landscape units characterized by different hydroecomorphological site conditions that are reflected in the distribution of soils and tree species. These conditions are determined by flooding frequency and duration, distance to river channels, elevation and water flow velocity. The influence of these environmental drivers on the stabilization of soil organic matter (SOM) has as yet not been investigated. Hence, the aim of our study is to link soil formation and its drivers with stabilizing processes of SOM in riparian floodplain forests. We investigated soils and sediments at two sites in the ash–maple–elm–oak alluvial forest zone (AMEO sites) and two sites in the willow-poplar alluvial forest zone (WiP sites) within the riparian zone of the Danube near Vienna (Austria). Sediments and soils were characterized based on texture, contents of organic carbon (OC), nitrogen, Fe oxides, and soil pH. Density fractionation was used to separate OC fractions in terms of stabilization process and resulting organic matter (OM) turnover time: the free light fraction (fast turnover), the light fraction occluded in aggregates (intermediate turnover) and the heavy fraction of OM associated tightly to mineral surfaces (slow turnover). At both sites, soil and sediment properties reflect the hydroecomorphological site conditions for formation of the landscape units in the riparian zone: Soils at AMEO sites develop during constant deposition of fine-textured sediment while water flow velocity is low. Progressing soil development causes a continuous decrease in OC content with increasing soil depth, mainly from fractions with fast and intermediate turnover. As a consequence the heavy fraction clearly dominates with around 90% of OC. Temporally variable flooding conditions with occurring turbulences found at WiP sites result in a discontinuous change of soil properties with increasing soil depth. Former topsoil horizons buried by huge amounts of sediments seem to keep the OC fractionation typical for topsoil horizons with extraordinarily high amounts of light fraction OM (free and occluded) representing 20–40% of total OC. The presented results confirm that sedimentation and soil formation are simultaneous processes at AMEO sites. At WiP sites both processes seem uncoupled with alternate phases of sedimentation and soil formation. Thus, the frequent burial of topsoil material formed at WiP sites seems to enable the conservation of unstable organic matter fractions at this part of active floodplains.
    Keywords: Fluvisol Formation ; Soil Organic Matter ; Density Fractionation ; Riparian Floodplains ; Soil Aggregates ; Riparian Forests ; Sciences (General) ; Geography ; Geology
    ISSN: 0341-8162
    E-ISSN: 1872-6887
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  • 3
    Language: English
    In: Journal of Plant Nutrition and Soil Science, February 2018, Vol.181(1), pp.31-35
    Description: Quantifying and understanding fluxes of methane (CH) and carbon dioxide (CO) in natural soil–plant–atmosphere systems are crucial to predict global climate change. Wetland herbaceous species or tree species at waterlogged sites are known to emit large amounts of CH. Upland forest soils are regarded as CH sinks and tree species like upland beech are not known to significantly emit CH. Yet, data are scarce and this assumption needs to be tested. We combined measurements of soil–atmosphere and stem–atmosphere fluxes of CO and CH and soil gas profiles to assess the contribution of the different ecosystem compartments at two upland beech forest sites in Central Europe in a case study. Soil was a net CH sink at both sites, though emissions were detected consistently from beech stems at one site. Although stem emissions from beech stems were high compared to known fluxes from other upland tree species, they were substantially lower compared to the strong CH sink of the soil. Yet, we observed extraordinarily large CH emissions from one beech tree that was 140% of the CH sink of the soil. The soil gas profile at this tree indicated CH production at a soil depth 〉 0.3 m, despite the net uptake of CH consistently observed at the soil surface. Field soil assessment showed strong redoximorphic color patterns in the adjacent soil and supports this evaluation. We hypothesize that there is a transport link between the soil and stem the root system representing a preferential transport mechanism for CH despite the fact that beech roots usually do not bear aerenchyma. The high mobility of gases requires a holistic view on the soil–plant–atmosphere system. Therefore, we recommend including field soil assessment and soil gas profiles measurements when investigating soil–atmosphere and stem–atmosphere fluxes to better understand the sources of gases and their transport mechanisms.
    Keywords: Ch 4 ; Soil Gas Profile ; Gas Flux ; Stem Gas Flux ; Co 2 ; Methanogenesis
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 4
    Language: English
    In: Geoderma, 01 July 2017, Vol.297, pp.61-69
    Description: The use of heavy machinery for timber harvesting causes soil damage, which may restrict forest soil functions over decades. Numerous studies have demonstrated the negative impact of soil compaction on soil physical properties, but the effects of compaction of forest soils on soil chemical and biological processes like the phosphorus availability are largely unknown. Aim of our study was to analyze the effect of skidding activity on the P dynamics on skid trails and the soil recovery ability after skidding. Furthermore, we wanted to assess if acid phosphatase activity is an appropriate indicator of soil structure damage after compaction. We investigated the phosphorus availability, acid phosphatase activity, TOC, pH value, and fine root density of soil samples from skid trails and from control plots without any skidding effect. We conducted our studies at three sites (Göttingen: Cambisols on limestone, Heide: Podzol on glacial drift and sand, and Solling: Cambisols at loess-covered sandstone) in Lower Saxony, Germany 10 to 40 years after last traffic impact in a space-for-time substitution. We observed mainly higher P concentrations and higher pH values at the wheel tracks than in the control. TOC was predominantly higher at the wheel tracks, but lower TOC at the wheel tracks was also found. In the acidic loams of the Solling region, the amount of mineralized phosphate was much higher in the tracks compared to the control areas 10 to 30 years after last traffic impact. This suggests a decoupling of P mineralization from P uptake in the wheel tracks for several decades. Furthermore, higher as well as lower phosphatase activity at the wheel tracks compared to the untrafficked control was found, but higher phosphatase activities at the wheel tracks were predominant. Acid phosphatase activity was strongly correlated with TOC, but did not correlate with the time since last traffic impact and the gas diffusivity of the soil. Therefore, our results did not confirm that acid phosphatase activity is an appropriate soil biological indicator of soil compaction and structural recovery.
    Keywords: Acid Phosphatase Activity ; P Availability ; Soil Compaction ; Soil Structure Recovery ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 5
    Language: English
    In: Geoderma, 15 February 2017, Vol.288, pp.204-212
    Description: Deadwood is a key factor in forest ecosystems, yet how it influences forest soil properties is uncertain. We hypothesized that changes in soil properties induced by deadwood mainly depend on the amount of released phenolic matter. Consequently we expected softwood- and hardwood-related deadwood effects on soil to be explained by unequal enrichment of phenolic substances. We measured differences in the quantity and composition of soil organic matter (SOM), pH, nutrient concentrations, and enzymatic activity between paired control and treatment points influenced by deadwood of silver fir ( Mill.) and European beech ( L.), and checked for correlations with total C and phenolic matter; the latter was quantified as aromaticity of water-extractable organic C through specific UV absorbance at 280 nm. Near fir deadwood, aromaticity and effective cation exchange capacity (CEC) increased while pH decreased. In comparison, concentrations of water-extractable organic C, effective CEC, exchangeable Ca and Mg , base saturation, and available molybdenum-reactive P increased near beech deadwood while exchangeable Al decreased. For fir deadwood, soil properties strongly correlated almost exclusively with total C. For beech deadwood, numerous strong correlations with aromaticity indicated that extractable phenolics influenced soil properties. These differences in correlations imply that deadwood affects soil through the composition of added phenolic matter, which would stem from differing decay processes and organisms. Decayed, particulate lignin from brown-rot in fir deadwood as opposed to oxidized, dissolved lignin from white-rot in beech deadwood would account for our observations.
    Keywords: Coarse Woody Debris ; Soil Chemistry ; Lignin ; Brown-Rot Fungi ; White-Rot Fungi ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 6
    In: Environmental Microbiology, June 2016, Vol.18(6), pp.1988-2000
    Description: Phosphorus () is an important macronutrient for all biota on earth but similarly a finite resource. Microorganisms play on both sides of the fence as they effectively mineralize organic and solubilize precipitated forms of soil phosphorus but conversely also take up and immobilize . Therefore, we analysed the role of microbes in two beech forest soils with high and low content by direct sequencing of metagenomic deoxyribonucleic acid. For inorganic solubilization, a significantly higher microbial potential was detected in the ‐rich soil. This trait especially referred to  olibacter usiatus, likewise one of the dominating species in the data sets. A higher microbial potential for efficient phosphate uptake systems () was detected in the ‐depleted soil. Genes involved in starvation response regulation (, ) were prevalent in both soils. This underlines the importance of effective phosphate (ho) regulon control for microorganisms to use alternative sources during phosphate limitation. Predicted genes were primarily harboured by hizobiales, ctinomycetales and cidobacteriales.
    Keywords: Soil Microbiology – Analysis ; Nucleic Acids – Analysis ; Phosphates – Analysis ; Forest Soils – Analysis ; Soil Phosphorus – Analysis;
    ISSN: 1462-2912
    E-ISSN: 1462-2920
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  • 7
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2016, Vol.179(4), pp.472-480
    Description: Among several environmental factors shaping soil microbial communities the impact of soil nutrients is of special interest. While continuous application mainly of N and P dramatically shifts community composition during fertilization, it remains unclear whether this effect is consistent in generic, unfertilized beech forest ecosystems of Germany, where differences in nutrient contents are mostly a result of the parental material and climatic conditions. We postulate that in such ecosystems nutrient effects are less pronounced due to the possibility of the soil microbiome to adapt to the corresponding conditions over decades and the vegetation acts as the major driver. To test this hypothesis, we investigated the bacterial community composition in five different German beech dominated forest soils, representing a natural gradient of total‐ and easily available mineral‐P. A community fingerprinting approach was performed using terminal‐Restriction Fragment Length Polymorphism analysis of the 16S rRNA gene, while abundance of bacteria was measured applying quantitative real‐time PCR. Bacterial communities at the five forest sites were distinctly separated, with strongest differences between the end‐members of the P‐gradient. However the majority of identified microbial groups (43%) were present at all sites, forming a core microbiome independent from the differences in soil chemical properties. Especially in the P‐deficient soil the abundance of unique bacterial groups was highly increased, indicating a special adaption of the community to P limitation at this site. In this regard Correspondence Analysis elucidated that exclusively soil pH significantly affected community composition at the investigated sites. In contrast soil C, N and P contents did mainly affect the overall abundance of bacteria.
    Keywords: Core Microbiome ; Forest Soil ; Nutrient Content ; Diversity
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 8
    In: Environmental Microbiology, September 2016, Vol.18(8), pp.2767-2767
    Description: Byline: Fabian Bergkemper, Anne Scholer, Marion Engel, Friederike Lang, Jaane Kruger, Michael Schloter, Stefanie Schulz ***** No abstract is available for this article. *****
    Keywords: Recycling ; Forest Soils ; Soil Microbiology;
    ISSN: 1462-2912
    E-ISSN: 1462-2920
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  • 9
    Language: English
    In: Plant and Soil, 2018, Vol.427(1), pp.53-69
    Description: Background and aims Phosphorus (P) availability is crucial for forest ecosystem productivity and soil organic matter (SOM) is an important source for P. This study was conducted to reveal carbon (C), nitrogen (N) and P distributions in functional SOM fractions. We hypothesised that (1) most of the organic P (P.sub.org) is part of the particulate SOM, (2) particulate SOM stores increasing share of P with decreasing soil P content and (3) the C:P.sub.org ratio of mineral-associated SOM is smaller than that of particulate SOM. Methods We analysed soil samples from five temperate forest sites (Fagus sylvatica) under different geological parent material with a wide range of total P concentrations. Density fractionation was used to separate free light fraction (fLF), particulate SOM occluded within soil aggregates (occluded light fraction; oLF), and mineral associated SOM (heavy fraction; HF). We determined the mass balance of P in these fractions, in addition to the C and N concentrations. Additionally, the P speciation of the topsoil was analysed by X-ray absorption near edge structure (XANES) spectroscopy at the P K-edge. Results The fLF contained 18-54% and the oLF 1-15% of total P (P.sub.tot). High percentage of P in these light fractions was associated to soil minerals. Phosphorous in particulate SOM within aggregates tend to increase with decreasing soil P. The HF containing mineral-associated OM, comprised 38-71% of P.sub.tot and their C:P.sub.org ratios were consistently lower than those of the fLF irrespective of the P status of the soil. Conclusions We show that all three functional SOM fractions contain variable amount of both organic and inorganic P species. The free light fraction shows no response to changing P stocks of soils.. Despite physically protected particulate SOM, oLF, becomes increasingly relevant as P cache in soils with declining P status.
    Keywords: Ecosystem nutrition ; Density fractions ; Soil organic matter ; C:N:P ratio ; Phosphorus ; P K-edge XANES
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 10
    Language: English
    In: Plant and Soil, 2018, Vol.427(1), pp.71-86
    Description: Background and aims Nanoparticles and colloids affect the mobilisation and availability of phosphorus for plants and microorganisms in soils. We aimed to give a description of colloid sizes and composition from forest soil profiles and to evaluate the size-related quality of colloids for P fixation. Methods We investigated the size-dependent elemental composition and the P content of water-dispersible colloids (WDC) isolated from five German (beech-dominated) forest soil profiles of varying bulk soil P content by field-flow fractionation (FFF) coupled to various detectors. Results Three size fractions of WDC were separated: (i) nanoparticles 25 nm (NP) rich in C.sub.org, (ii) fine colloids (25 nm-240 nm; FC) composed mainly of C.sub.org, Fe and Al, probably as associations of Fe- and Al- (hydr)oxides and organic matter, and (iii) medium-sized colloids (240 nm-500 nm; MC), rich in Fe, Al and Si, indicating the presence of phyllosilicates. The P concentration in the overall WDC was up to 16 times higher compared to the bulk soil. The NP content decreased with increasing soil depth while the FC and MC showed a local maximum in the mineral topsoil due to soil acidification, although variant distributions in the subsoil were observed. NP were of great relevance for P binding in the organic surface layers, whereas FC- and MC-associated P dominated in the Ah horizon. Conclusion The nanoparticles and colloids appeared to be of high relevance as P carriers in the forest surface soils studied, regardless of the bulk soil P content.
    Keywords: Colloids ; Field-flow fractionation ; Forest soil ; Nanoparticles ; Phosphorus
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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