Organic Topsoils Research Articles

Metaproteomics reveals functional partitioning and vegetational variation among permafrost-affected Arctic soil bacterial communities.

Microbial activity in Arctic soils controls the cycling of significant stores of organic carbon and nutrients. We studied in situ processes in Alaskan soils using original metaproteomic methods in order to relate important heterotrophic functions to microbial taxa and to understand the microbial response to Arctic greening. Major bacterial groups show strong metabolic specialization in organic topsoils. α-/β-/γ-Proteobacteria specialized in the acquisition of small, soluble compounds, whereas Acidobacteria, Actinobacteria, and other detritosphere groups specialized in the degradation of plant-derived polymers. α-/β-/γ-Proteobacteria dominated the expression of transporters for common root exudates and limiting nitrogenous compounds, supporting an ecological model of dependence upon plants for carbon and competition with plants for nitrogen. Detritosphere groups specialized in distinct substrates, with Acidobacteria producing the most enzymes for hemicellulose depolymerization. Acidobacteria was the most active group across the three plant ecotypes sampled-the largely nonvascular, lower biomass intertussock and the largely vascular, higher biomass tussock and shrub. Functional partitioning among bacterial groups was stable between plant ecotypes, but certain functions associated with α-/β-/γ-Proteobacteria were more strongly expressed in higher biomass ecotypes. We show that refined metaproteomic approaches can elucidate soil microbial ecology as well as biogeochemical trajectories of major carbon stocks. IMPORTANCE The Arctic is warming twice as fast as the rest of the planet, and Arctic soils currently store twice as much carbon as the entire atmosphere-two facts that make understanding how Arctic soil microbial communities are responding to climate change particularly urgent. Greening of vegetation cover across the Arctic landscape is one of the most prominent climate-driven shifts in Arctic terrestrial ecology, with potentially profound effects on biogeochemical cycling by the soil microbiome. Here we use metaproteomics to document microbial metabolic functions that drive soil carbon and nutrient cycling processes in an Arctic tundra landscape. We identify functional roles among bacterial taxonomic groups that are largely stable across vegetation types, with certain functions strongly expressed by rhizosphere groups reflecting a community metabolic response to greening.

Accurate Measurements of Forest Soil Water Content Using FDR Sensors Require Empirical In Situ (Re)Calibration

Monitoring volumetric soil water content (θv) is the key for assessing water availability and nutrient fluxes. This study evaluated the empirical accuracy of θv measurements using standard and in situ calibrated frequency domain reflectometers (FDR) with gravimetric water content and bulk density measurements of 1512 samples gathered from 15 profiles across 5 ICP Forests level II intensive monitoring plots. The predicted θv, calibrated with standard functions, predominantly underestimated the real water content. The measurement error exceeded the threshold of 0.03 m3 m−3 in 93% of all soil layers. Layer specific calibration removed bias and reduced the overall prediction error with a factor up to 2.8. A simple linear regression often provided the best calibration model; temperature correction was helpful in specific cases. To adequately remove bias in our study plots, a calibration dataset of up to 24 monthly observations was required for topsoils (whereas 12 observations sufficed for subsoils). Based on estimated precision errors, 3 sensors per soil layer proved to be sufficient, while up to 16 sensors are needed to meet the required accuracy in organic topsoils. Validating FDR sensor outputs using in situ gravimetric measurements is essential for quality control and assurance of long term θv monitoring and for improving site specific instrumentalization.

Mapping of Agricultural Subsurface Drainage Systems Using a Frequency-Domain Ground Penetrating Radar and Evaluating Its Performance Using a Single-Frequency Multi-Receiver Electromagnetic Induction Instrument.

Subsurface drainage systems are commonly used to remove surplus water from the soil profile of a poorly drained farmland. Traditional methods for drainage mapping involve the use of tile probes and trenching equipment that are time-consuming, labor-intensive, and invasive, thereby entailing an inherent risk of damaging the drainpipes. Effective and efficient methods are needed in order to map the buried drain lines: (1) to comprehend the processes of leaching and offsite release of nutrients and pesticides and (2) for the installation of a new set of drain lines between the old ones to enhance the soil water removal. Non-invasive geophysical soil sensors provide a potential alternative solution. Previous research has mainly showcased the use of time-domain ground penetrating radar, with variable success, depending on local soil and hydrological conditions and the central frequency of the specific equipment used. The objectives of this study were: (1) to test the use of a stepped-frequency continuous wave three-dimensional ground penetrating radar (3D-GPR) with a wide antenna array for subsurface drainage mapping and (2) to evaluate its performance with the use of a single-frequency multi-receiver electromagnetic induction (EMI) sensor in-combination. This sensor combination was evaluated on twelve different study sites with various soil types with textures ranging from sand to clay till. While the 3D-GPR showed a high success rate in finding the drainpipes at five sites (sandy, sandy loam, loamy sand, and organic topsoils), the results at the other seven sites were less successful due to the limited penetration depth of the 3D-GPR signal. The results suggest that the electrical conductivity estimates produced by the inversion of apparent electrical conductivity data measured by the EMI sensor could be a useful proxy for explaining the success achieved by the 3D-GPR in finding the drain lines.

Modern and historical tropical cyclone and tsunami deposits at the coast of Myanmar: Implications for their identification and preservation in the geological record

AbstractThe catastrophic storm surge of tropical cyclone Nargis in May 2008 demonstrated Myanmar's exposure to coastal flooding. The investigation of sediments left by tropical cyclone Nargis and its predecessors is an important contribution to prepare for the impact of future tropical cyclones and tsunamis in the region, because they may extend the database for long‐term hazard assessment beyond the relatively short instrumental and historical record. This study, for the first time, presents deposits of modern and historical tropical cyclones and tsunamis from the coast of Myanmar. The aim is to establish regional sedimentary characteristics that may help to identify and discriminate cyclones and tsunamis in the geological record, and to document post‐depositional changes due to tropical weathering in the first years after deposition. These findings if used to interpret older deposits will extend the existing instrumental record of flooding events in Myanmar. Evaluating deposits that can be related to specific events, such as the 2006 tropical cyclone Mala and the 2004 Indian Ocean tsunami, indicates similar sedimentary characteristics for both types of sediments. Landward thinning and fining trends, littoral sediment sources and sharp lower contacts allow for the differentiation from underlying deposits, while discrimination between tropical cyclone and tsunami origin is challenging based on the applied methods. The modern analogues also demonstrate a rather low preservation potential of the sand sheets due to carbonate dissolution, formation of organic top soils, and coastal erosion. However, in coastal depressions sand sheets of sufficient thickness (>10 cm) may be preserved where the shoreline is prograding or stable. In the most seaward swale of a beach‐ridge plain at the Rakhine coast, two sand sheets have been identified in addition to the deposits of 2006 tropical cyclone Mala. Based on a combination of optically stimulated luminescence, radiocarbon and 137Cs dating, the younger sand layer is related to 1982 tropical cyclone Gwa, while the older sand layer is most probably the result of an event that took place prior to 1950. Comparison with historical records indicates that the archive is only sensitive to tropical cyclones of category 4 (or higher) with landfall directly in or a few tens of kilometres north of the study area. While the presented tropical cyclone records are restricted to the last 100 years, optically stimulated luminescence ages of the beach ridges indicate that the swales landward of the one investigated in this study might provide tropical cyclone information for at least the past 700 years.

Peat capping: Natural capping of wet landfills by peat formation

Given the bioremediation potential of peat, natural capping of landfills in wetlands with a “peat cap” could provide a sustainable addition to regular capping methods using basal liners with limited life-spans and sand. It is unknown, however, which initial conditions optimise growth of this “peat cap” on top of a sand layer. Here, we tested the combined effects of topsoil addition (clay or organic soil) and vegetation type (Typha latifolia, T. angustifolia, Stratiotes aloides and submerged spp.) on net ecosystem C exchange and water quality in 18 sandy basins situated in a constructed wetland on top of a landfill. Although the highest net C sequestration rates occurred in Typha stands on sand, due to lower decomposition-related C losses as compared to clay and organic topsoils, vegetation development was slow and its cover was very low (15%) compared to clay (40%) and organic topsoils (70%). As this strongly impeded the build-up of a uniform peat layer, we conclude that, within a restricted time frame, the application of nutrient-rich topsoils is still necessary for sufficient biomass production to accumulate organic material. By recycling local soils, the accompanying initial C loss becomes negligible on a landscape scale.

Arctic and Subarctic Natural Soils Emit Chloroform and Brominated Analogues by Alkaline Hydrolysis of Trihaloacetyl Compounds.

There has been increasing recognition of the occurrence of natural, halogenated organic compounds in marine and terrestrial environments. Chloroform is an example of a halogenated organic compound with natural formation as its primary source. Chloroform emission from soil has been reported from diverse Arctic, temperate, and (sub)tropical ecosystems. The terrestrial environment is a significant source to the atmosphere, but little is known about the formation pathway of chloroform in soil. Here, we present evidence that chloroform is formed through the hydrolysis of trichloroacetyl compounds in natural, organic-rich soils. In situ emissions of chloroform from soil in nine Arctic and subarctic ecosystems were linked to soil trichloroacetyl turnover. The residence time from formation of the trichloroacetyl compounds in soil to the release of chloroform to the atmosphere varied between 1 and 116 active months in unfrozen topsoil, depending on soil pH. Nonspecific halogenation that leads to trihaloacetyl formation does not discriminate between chloride and bromide, and brominated analogues were formed alongside chloroform. Soil may therefore be a previously unrecognized, natural source of brominated haloforms. The formation pathway of haloforms through trihaloacetyl compounds can most likely be extended to other ecosystems with organic topsoils.

Assessment of Noah land surface model with various runoff parameterizations over a Tibetan river

AbstractRunoff parameterizations currently adopted by the (i) Noah‐MP model, (ii) Community Land Model (CLM), and (iii) CLM with variable infiltration capacity hydrology (CLM‐VIC) are incorporated into the structure of Noah land surface model, and the impact of these parameterizations on the runoff simulations is investigated for a Tibetan river. Four numerical experiments are conducted with the default Noah and three aforementioned runoff parameterizations. Each experiment is forced with the same set of atmospheric forcing, vegetation, and soil parameters. In addition, the Community Earth System Model database provides the maximum surface saturated area parameter for the Noah‐MP and CLM parameterizations. A single‐year recurrent spin‐up is adopted for the initialization of each model run to achieve equilibrium states. Comparison with discharge measurements shows that each runoff parameterization produces significant differences in the separation of total runoff into surface and subsurface components and that the soil water storage‐based parameterizations (Noah and CLM‐VIC) outperform the groundwater table‐based parameterizations (Noah‐MP and CLM) for the seasonally frozen and high‐altitude Tibetan river. A parameter sensitivity experiment illustrates that this underperformance of the groundwater table‐based parameterizations cannot be resolved through calibration. Further analyses demonstrate that the simulations of other surface water and energy budget components are insensitive to the selected runoff parameterizations, due to the strong control of the atmosphere on simulated land surface fluxes induced by the diurnal dependence of the roughness length for heat transfer and the large water retention capacity of the highly organic top soils over the plateau.

Microbial community composition shapes enzyme patterns in topsoil and subsoil horizons along a latitudinal transect in Western Siberia

Soil horizons below 30 cm depth contain about 60% of the organic carbon stored in soils. Although insight into the physical and chemical stabilization of soil organic matter (SOM) and into microbial community composition in these horizons is being gained, information on microbial functions of subsoil microbial communities and on associated microbially-mediated processes remains sparse. To identify possible controls on enzyme patterns, we correlated enzyme patterns with biotic and abiotic soil parameters, as well as with microbial community composition, estimated using phospholipid fatty acid profiles. Enzyme patterns (i.e. distance-matrixes calculated from these enzyme activities) were calculated from the activities of six extracellular enzymes (cellobiohydrolase, leucine-amino-peptidase, N-acetylglucosaminidase, chitotriosidase, phosphatase and phenoloxidase), which had been measured in soil samples from organic topsoil horizons, mineral topsoil horizons, and mineral subsoil horizons from seven ecosystems along a 1500 km latitudinal transect in Western Siberia. We found that hydrolytic enzyme activities decreased rapidly with depth, whereas oxidative enzyme activities in mineral horizons were as high as, or higher than in organic topsoil horizons. Enzyme patterns varied more strongly between ecosystems in mineral subsoil horizons than in organic topsoils. The enzyme patterns in topsoil horizons were correlated with SOM content (i.e., C and N content) and microbial community composition. In contrast, the enzyme patterns in mineral subsoil horizons were related to water content, soil pH and microbial community composition. The lack of correlation between enzyme patterns and SOM quantity in the mineral subsoils suggests that SOM chemistry, spatial separation or physical stabilization of SOM rather than SOM content might determine substrate availability for enzymatic breakdown. The correlation of microbial community composition and enzyme patterns in all horizons, suggests that microbial community composition shapes enzyme patterns and might act as a modifier for the usual dependency of decomposition rates on SOM content or C/N ratios.

Iron speciation in soils and soil aggregates by synchrotron‐based X‐ray microspectroscopy (XANES,μ‐XANES)

SummaryIron speciation in soils is still poorly understood. We have investigated inorganic and organic standard substances, diluted mixtures of common Fe minerals in soils (pyrite, ferrihydrite, goethite), soils in a forested watershed which constitute a toposequence with a hydrological gradient (Dystric Cambisol, Dystric Planosol, Rheic Histosol), and microsites of a dissected soil aggregate by X‐ray Absorption Near Edge Spectroscopy (XANES) at the iron K‐edge (7112 eV) to identify different Fe(II) and Fe(III) components. We calculated the pre‐edge peak centroid energy of all spectra and quantified the contribution of different organic and inorganic Fe‐bearing compounds by Linear Combination Fitting (LCF) conducted on the entire spectrum (E = 7085–7240 eV) and on the pre‐edge peak. Fe‐XANES conducted on organic and inorganic standards and on synthetic mixtures of pyrite, ferrihydrite and goethite showed that by calculating the pre‐edge peak centroid energy, the Fe(II)/Fe(III) ratio of different Fe‐bearing minerals (Fe sulphides, Fe oxyhydroxides) in mineral mixtures and soils can be quantified with reasonable accuracy. A more accurate quantification of the Fe(II)/Fe(III) ratio was possible with LCF conducted on the entire XANES spectrum. For the soil toposequence, an increased groundwater influence from the Cambisol to the Histosol was reflected in a larger contribution of Fe(II) compounds (Fe(II) silicate, Fe monosulphide, pyrite) and a smaller contribution of Fe(III) oxyhydroxides (ferrihydrite, goethite) to total iron both in the topsoil and the subsoil. In the organic topsoils, organically bonded Fe (33–45% of total Fe) was 100% Fe(III). For different microsites in the dissected aggregate, spatial resolution ofμ‐XANES revealed different proportions of Fe(II) and Fe(III) compounds. Fe K‐edge XANES andμ‐XANES allows an approximate quantification of Fe(II) and Fe(III) and different Fe compounds in soils and (sub)micron regions of soil sections, such as mottles, concretions, and rhizosphere regions, thus opening new perspectives in soil research.

Changes in microbial biomass and nitrogen turnover in acidic organic soils following liming

The effect of liming on microbial activity and N transformations was examined in four very acidic, organic topsoils to help explain reports of poor growth of conifers on some such soils. Data were obtained from laboratory incubations and from a long-term field experiment. Liming to a pH near 6.5 caused soil respiration and microbial biomass to at least double in the first 4 d, mainly due to the proliferation of indigenous acid intolerant bacteria. Soil respiration then declined rapidly but microbial biomass less so, and in two soils, biomass remained significantly greater than the control beyond 101 d. Liming caused an initial increase in net N mineralization in all soils, but beyond 34 d, it became similar to or substantially less than the control. Nitrification in the limed soils increased rapidly at around 30 d. The greatest reduction in N mineralization occurred in two soils with the greatest C-to-N ratio. Immobilization of N in the microbial biomass could not account for the very small N mineralization rates observed in the long term, but a relatively small increase in the N concentration of the stableresidual soil organic matter could. Small net N mineralization rates in limed organic soils with a large C-to-N ratio that could persist for more than 10 y may cause N stress in single species stands of trees on plantation forest, but it is unlikely to decrease the growth of vegetation in species-rich communities.

Fossil power without carbon dioxide: realistic or not

This paper is not a scientific report, but is meant to be a reasonably light read about carbon dioxide, and the possibility of separating it from the exhaust of a power plant. It is sometimes said that the separation of carbon dioxide (CO2) from the exhaust of a power plant is not feasible. It is in fact technically possible, but it will cost money and efficiency. The real problem with CO2 is where to store it. At present, carbon is the most important energy resource in the world: carbon in oil and carbon in coal. Carbon is also the most important carrier of energy in biomass. If an increasing CO2 concentration in the air causes a climatic change, and if this is considered so damaging that something has to be done about it, then one should try to cut down on CO2 production from all sources wherever it is cheapest, and possibly also try to separate CO2 and bind it wherever it is cheapest. It is often said that only half of the CO2 that is released from the burning of fossil fuel is actually added to the atmosphere. Most of the missing half can then only 'disappear', dissolved in seawater and biologically bound in organic sediments, growing vegetation and topsoils. Our chance of controlling the greenhouse effect could lie as much in a good understanding of these processes as in cutting down on the production of CO2. All ways must be tried.

Properties of Slightly Organic Topsoils

The effect of small increases in organic content on the classification and engineering properties, such as specific gravity, Atterberg limits, compaction, and compressibility, of several natural soils and slightly organic soil mixture is investigated; emphasis is placed on slightly organic cells, as opposed to highly organic soils, such as peats and muck. The specific objective of this study is to provide the engineer in charge of construction or inspection, or both, with improved guidelines for determining the engineering suitability of slightly organic topsoils. The organic burn or loss on ignition test was found to be not generally reliable for use on slightly organic soils, and an H2O2 digestion procedure is proposed as an index of organic content. Increasing the organic content of a soil is found to increase both the Liquid Limit and the Plasticity Index, with a significantly greater increase in the Liquid Limit. Also, if the organic content is around 0.5 % to 1.0 % according to the H 2 O 2 digestion test, significant differences in compaction and compressibility characteristics occur with only a slight change in the organic content.