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Berlin Brandenburg

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  • AGRIS (United Nations, Food and Agriculture Organization)  (24)
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  • 1
    Language: English
    In: Soil biology & biochemistry, 2011, Vol.43, pp.280-286
    Description: Microbial communities exist and are active in a complex 3-D physical framework which can cause a variety of micro-environments to develop that are more or less suitable for microbial growth, activity and survival. If there is a significant microbial biogeography at the pore scale in soil, then the relationship between microbial diversity and ecosystem function is likely to be affected by micro-environmental variations at the pore scale. In this laboratory study we show that there is a significant pore-scale microbial biogeography by labelling microbial communities in different pore size classes of undisturbed soil cores with 13C-labelled fructose (a soluble, labile substrate). This was achieved by adding the substrate solution to the samples at different matric potentials (−100 kPa, −3.15 kPa and −1 kPa; placing the substrate in pores with maximum diameter of 0.97, 9.7 and 97 μm, respectively) and incubating the samples for two weeks. The mineralisation of soil organic carbon and fructose was measured as CO2 and 13C–CO2, respectively, in the jar headspace throughout the incubation. At the end of incubation we analysed the total microbial community structure using PLFA. The structure of microbial communities in different pore size classes was measured by PLFA stable isotope probing. Total PLFA profiles suggested that there was little effect of the incubation conditions on microbial community structure. However, labelled PLFA profiles showed that microbial community structure differed significantly among pore size classes, the differences being due primarily to variations in the abundance of mono-unsaturated lipids (Gram-biomarkers) and of the fungal biomarker (C18:2(9,12)). This is the first evidence for a significant microbial biogeography at the pore scale in undisturbed soil cores. ; Includes references ; p. 280-286.
    Keywords: Soil Organic Carbon ; Soil Bacteria ; Soil Pore System ; Soil Matric Potential ; Functional Diversity ; Biogeography ; Soil Ecology ; Isotope Labeling ; Stable Isotopes ; Microhabitats ; Headspace Analysis ; Soil Microorganisms ; Soil Fungi ; Carbon ; Fructose ; Mineralization ; Microbial Ecology ; Species Diversity
    ISSN: 0038-0717
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 2
    Language: English
    In: Soil biology & biochemistry, 2010, Vol.42, pp.1640-1642
    Description: A miniaturised method developed to measure the mineralisation of 13C-labelled organic compounds in small soil samples is presented. Soil samples (〈0.5 g) were placed in wells of microtiter plates with CO2 traps (NaOH-soaked glass microfiber filters) and amended with 13C-labelled substrate. The microtiter plate was covered with a seal and placed in a microplate clamp system to ensure that each well was airtight. After incubation, the CO2 traps were transferred to tightly sealed glass phials under CO2-free atmosphere and the 13C-labelled CO2 was released by addition of H3PO4. The CO2 was measured by micro-GC and its isotopic signature was determined using a GC-IRMS. The qualitative and quantitative efficiency of the microplate system was demonstrated by comparison with direct measurement of CO2 in the headspace of phials in which similarly treated soil samples had been incubated. The two methods showed similar mineralisation rates for added 13C-substrates but the apparent mineralisation of soil organic matter was greater with the microtiter plate method. The microplate system presented here is suitable for studying the mineralisation of different kinds of 13C-labelled substrates in small soil samples and allows analysis of functional and molecular characteristics on the same micro-samples. ; Includes references ; p. 1640-1642.
    Keywords: Soil Organic Carbon ; Laboratory Techniques ; Isotope Labeling ; New Methods ; Methodology ; Stable Isotopes ; Soil Sampling ; Carbon Dioxide ; Gas Chromatography ; Gas Emissions ; Headspace Analysis ; Soil Microorganisms ; Carbon ; Mineralization ; Phosphoric Acid ; Sample Size ; Microtiter Plates ; Miniaturized Methods
    ISSN: 0038-0717
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 3
    In: Global Change Biology, January 2010, Vol.16(1), pp.416-426
    Description: It is estimated that in excess of 50% of the soil carbon stock is found in the subsoil (below 20–30 cm). Despite this very few studies have paid attention to the subsoil. Although surface and subsurface horizons differ in pedological, environmental and physicochemical features, which are all likely to affect the mechanisms and biological actors involved, models of carbon dynamics tend to assume that the underlying processes are identical in all horizons, but with lower gross fluxes in the subsurface. The aim of this study was to test this assumption by analysing factors governing organic matter decomposition in topsoil (from depths of 5–10 cm) and subsoil (from depths of 80–100 cm). To this end, we established incubations that lasted 51 days, in which factors that were thought to control organic matter mineralization were altered: oxygen concentration, soil structure and the energetic and nutritional status. At the end of the incubation period, the microbial biomass was measured and the community level physiological profiles established. The mineralization per unit organic carbon proved to be as important in the subsoil as it was in surface samples, in spite of lower carbon contents and different catabolic profiles. Differences in the treatment effects indicated that the controls on C dynamics were different in topsoil and subsoil: disrupting the structure of the subsoil caused a 75% increase in mineralization while the surface samples remained unaffected. On the other hand, a significant priming affect was found in the topsoil but not in the subsoil samples. Spatial heterogeneity in carbon content, respiration and microbial communities was greater in subsoil than in topsoil at the field scale. These data suggest greater attention should be paid to the subsoil if global C dynamics is to be fully understood.
    Keywords: C ; C Dynamics ; Microbial Community Structure ; Stable Isotopes ; Subsoil
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 4
    Language: English
    In: Soil biology & biochemistry, 2013, Vol.66, pp.69-77
    Description: Soil microorganisms are responsible for organic matter decomposition processes that regulate soil carbon storage and mineralisation to CO₂. Climate change is predicted to increase the frequency of drought events, with uncertain consequences for soil microbial communities. In this study we tested the hypothesis that agricultural management used to enhance soil carbon stocks would increase the stability of microbial community structure and activity in response to water-stress. Soil was sampled from a long-term field trial with three soil carbon management systems and was used in a laboratory study of the effect of a dry–wet cycle on organic C mineralisation and microbial community structure. After a drying–rewetting event, soil microcosms were maintained wet and microbial community structure and abundance as well as microbial respiration were measured for four weeks. The results showed that the NO-TILL management system, with the highest soil organic matter content and respiration rate, had a distinct bacterial community structure relative to the conventional and the TILL without fertiliser systems. In all management systems, the rewetting event clearly modified microbial community structure and activity. Both returned to their pre-drought state after 28 days. However, the magnitude of variation of C mineralisation was lower (i.e. the resistance to stress was higher) in the NO-TILL system. The genetic structure of the NO-TILL bacterial communities was most modified by water-stress and exhibited a slower recovery rate. This suggests that land use management can increase microbial functional resistance to drought stress via the establishment of bacterial communities with particular metabolic capacities. Nevertheless, the resilience rates of C mineralisation were similar among management regimes, suggesting that similar mechanisms occur, maybe due to a common soil microbial community legacy. ; p. 69-77.
    Keywords: Soil Bacteria ; Carbon Sequestration ; Drought Tolerance ; No-Tillage ; Soil Organic Matter ; Organic Matter ; Field Experimentation ; Bacterial Communities ; Soil Ecology ; Climate Change ; Carbon Dioxide ; Drought ; Water Stress ; Agricultural Management ; Carbon Sinks ; Carbon ; Land Use Planning ; Management Systems ; Mineralization ; Stress Tolerance ; Respiratory Rate ; Community Structure ; Conventional Tillage ; Soil
    ISSN: 0038-0717
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 5
    Language: English
    In: Journal of Ecology, 1 May 2011, Vol.99(3), pp.828-837
    Description: 1. Declines in availability of plant resources to pollinators are a major cause of pollinator loss. The management of plant communities to enhance floral resources is often proposed as a way to sustain pollinator populations. Nectar, the main energetic resource for pollinators, plays a central role in behaviour and composition of pollinator communities. Abiotic and biotic factors are known to influence nectar traits at both the species and community levels, but the impact of plant community composition itself has never been investigated. 2. Below-ground interactions in plant communities can induce changes in plant development through (i) plant-derived litter amendment of the soil and (ii) competition for soil resources between plants. We tested how plant below-ground interactions affect above-ground nectar traits involved in plant attractiveness to pollinators. 3. A short-term pot experiment was carried out with three temperate grassland species Mimulus guttatus, Lamium amplexicaule, and Medicago sativa, showing distinct litter stoichiometry and competitive abilities for soil resources. Litter amendment (none, mono and tri-specific litter) and plant interaction treatments (monocultures, two- and three-species mixtures) were crossed in a factorial design. 4. Litter amendment to the soil led to an increase in total nectar sugar content in L. amplexicaule plants but not in the two other species. We also found that the presence of M. guttatus, a competitive species, reduced the total nectar sugar content in L. amplexicaule through a concomitant decrease in nectar volume per flower and in floral display size, but not in other species. Species-specific responses of nectar traits to variation in soil nitrogen availability were thus observed, suggesting consequences for plant species and community attractiveness to pollinators. However, we did not find evidence that the legume M. sativa affected nectar traits of any neighbouring plants. 5. Synthesis. Our results demonstrate that litter inputs and competition between plants for soil resources can alter nectar traits linked to plant attractiveness to pollinators. This supports the idea that below-ground plant—plant interactions for soil resources can influence above-ground plant— plant interactions for pollination services. This offers promising perspectives in studying the role of below-ground—above-ground interactions on higher trophic levels.
    Keywords: Biological sciences -- Biology -- Botany ; Biological sciences -- Biology -- Botany ; Applied sciences -- Materials science -- Materials ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Biology -- Botany ; Biological sciences -- Biochemistry -- Biomolecules ; Biological sciences -- Ecology -- Human ecology ; Biological sciences -- Ecology -- Natural resources ; Environmental studies -- Environmental sciences -- Developmental biology ; Biological sciences -- Biology -- Developmental biology
    ISSN: 00220477
    E-ISSN: 13652745
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  • 6
    In: Functional Ecology, December 2014, Vol.28(6), pp.1523-1533
    Description: A major question in ecology is to know how ecosystem function is affected by the number of species. After two decades of research, the nature, shape, and causes of the relationships between biodiversity and ecosystem functioning remain unresolved. Huston ([Huston, M.A., 1997]) suggested that a statistical ‘sampling effect’ for a few dominant species produced the patterns observed in experiments, while Tilman et al. ([Tilman, D., 1997a]) argued that the observed responses were due to the number of species rather than the properties of a few. Here, we present a general, theoretical and parsimonious model using combinatorial probabilities to describe the assembly effect as a probabilistic process. Our basic assumption is that community function is determined by random drawing from a fixed species pool composed of three classes of species. The species classes differ in their effect on community function and are ordered in a simple dominance hierarchy (subordinate, dominant and super‐dominant species). Community function is determined by prevalent dominance rules: the dominance by the majority of species mimics the effect of dominant species, i.e. the function is determined by the dominant or super‐dominant species class the most numerous within the community; the dominance by the presence of species mimics the effect of keystone species, i.e. the function is determined by the species that is ranked highest in the dominance hierarchy. The model produces significant fits to four experimental data sets obtained for plant and microbial communities, including monotonic and hump‐shaped curves. The results indicate that the model gave good fits under both the dominance rules in any data set, suggesting that the random sampling effect provides a parsimonious explanation for the various relationships observed in diversity‐ecosystem functioning experiments. The model describes a random assembly process that produces variation in ecosystem functioning in response to number of species selected from a regional species pool composed of several classes of species differing in their ecosystem effects and relative dominance. This simple model reproduces all shapes of diversity‐ecosystem functioning relationships reported in the experimental literature. The results suggest that the multi‐faceted response of ecosystems to biodiversity may be nothing more than manifestations of random assembly effects and variation in species properties. Lay
    Keywords: Assembly Process ; Biological Interactions ; Dominance ; Keystone ; Modelling ; Probability ; Sampling Effect ; Theoretical Ecology
    ISSN: 0269-8463
    E-ISSN: 1365-2435
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  • 7
    Language: English
    In: Microbial ecology, 2015, Vol.70(3), pp.809-818
    Description: Many studies have assessed the responses of soil microbial functional groups to increases in atmospheric CO₂ or N deposition alone and more rarely in combination. However, the effects of elevated CO₂ and N on the (de)coupling between different microbial functional groups (e.g., different groups of nitrifiers) have been barely studied, despite potential consequences for ecosystem functioning. Here, we investigated the short-term combined effects of elevated CO₂ and N supply on the abundances of the four main microbial groups involved in soil nitrification: ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (belonging to the genera Nitrobacter and Nitrospira) in grassland mesocosms. AOB and AOA abundances responded differently to the treatments: N addition increased AOB abundance, but did not alter AOA abundance. Nitrobacter and Nitrospira abundances also showed contrasted responses to the treatments: N addition increased Nitrobacter abundance, but decreased Nitrospira abundance. Our results support the idea of a niche differentiation between AOB and AOA, and between Nitrobacter and Nitrospira. AOB and Nitrobacter were both promoted at high N and C conditions (and low soil water content for Nitrobacter), while AOA and Nitrospira were favored at low N and C conditions (and high soil water content for Nitrospira). In addition, Nitrobacter abundance was positively correlated to AOB abundance and Nitrospira abundance to AOA abundance. Our results suggest that the couplings between ammonia and nitrite oxidizers are influenced by soil N availability. Multiple environmental changes may thus elicit rapid and contrasted responses between and among the soil ammonia and nitrite oxidizers due to their different ecological requirements. ; p. 809-818.
    Keywords: Soil Water Content ; Nitrospira ; Ammonia ; Ecosystems ; Nitrogen-Fixing Bacteria ; Carbon Dioxide ; Nitrogen ; Oxidants ; Soil Water ; Nitrification ; Grasslands ; Nitrobacter ; Nitrites
    ISSN: 0095-3628
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  • 8
    Language: English
    In: Biogeochemistry, 09 September 2011, Vol.106, pp.5-21
    Description: he soil microbial biomass (SMB) is known to participate in key soil processes such as the decomposition of soil organic matter (SOM). However, its contribution to the isotopic composition of the SOM is not clear yet. Shifts in the 13C and 15N natural abundances of the SMB and SOM fractions...
    Keywords: Environmental Sciences ; Environmental Sciences ; Biology ; Geology ; Chemistry
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 9
    Language: English
    In: Environmental Pollution, 2009, Vol.157(11), pp.2985-2993
    Description: The biodegradation of nonextractable residues (NER) of pesticides in soil is still poorly understood. The aim of this study was to evaluate the influence of NER ageing and fresh soil addition on the microbial communities responsible for their mineralisation. Soil containing either 15 or...
    Keywords: Environmental Sciences ; Environmental and Society ; Pesticides ; Nonextractable Residues ; 13c Labelling ; Soil Microbial Communities ; Biodegradation  ; Engineering ; Environmental Sciences ; Anatomy & Physiology
    ISSN: 0269-7491
    E-ISSN: 1873-6424
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  • 10
    Language: English
    In: European journal of soil biology, 2013, Vol.58, pp.81-90
    Description: Soil microbial communities live in the soil pore network and therefore the access they have to organic substrate, oxygen and water depends on how this network is structured. In this experimental study, the relationship between soil structure and soil organic matter dynamics was investigated by measuring the kinetics of organic carbon decomposition in samples that varied in the physical structure of the soil pore network. Soil cores with different structures (undisturbed, sieved and disaggregated by agitation in water), but with the same bulk density, were incubated and the mineralisation of native and added (¹³C-labelled substrates, fructose and vanillin) organic carbon was measured for a period of 127 days. The incubation was commenced after the immediate effects of the perturbations caused by the soil structural treatments had dissipated. At the end of the incubation, the microbial biomass and microbial community structure were determined. It was found that the respiration kinetics were not related to soil structural parameters, which were determined using X-ray micro-CT. The structure treatments had no significant effect on the mineralisation of soil or added organic carbon, despite the significantly different physical environments. However, the microbial community structure of the undisturbed and dispersed samples were significantly different. These results indicate that neither decomposer access to organic substrate nor the environmental conditions in which decomposition occurred were impaired by the soil structure treatments and suggest that the controls on carbon dynamics may take place at scales below those that were manipulated in this experiment. ; p. 81-90.
    Keywords: Environmental Factors ; Bulk Density ; Oxygen ; Soil Pore System ; Soil Organic Matter ; Microbial Biomass ; Vanillin ; Soil Microorganisms ; Microbial Communities ; Carbon ; Fructose ; Mineralization ; Agitation ; Community Structure ; X-Radiation
    ISSN: 1164-5563
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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