Soil Organic Carbon and Geochemical Characteristics on Different Rocks and Their Significance for Carbon Cycles

Soil organic carbon (SOC) is significant for soil quality and global carbon cycles. SOC was observed to be related to soil geochemistry, and soils originating from different bedrocks have different geochemical properties, but the effect of bedrock on SOC is still undefined. Soils overlying different bedrocks in Zhenxiong County and Weixin County were sampled. Specifically, soils in the mineral horizon, which are less affected by the external environment than surface soils, are focused on to reveal the effect of bedrock on SOC. Al/Ti, Fe/Ti, and Al/Fe indicate a soil–rock successive relationship. SOC contents in the mineral horizon are 0.19–2.74% (1.24% on average), and those in the surface horizon are 1.26–4.01% (2.63% on average). SOC contents in the surface and mineral horizons of the same bedrock are significantly positively correlated, implying that the bedrock is an important factor affecting SOC. SOC in the mineral horizon is related to the first transition metal ions. Significantly, positive correlations of SOC (p < 0.01) with Co, Cu, Ti, V, and Zn, and a positive correlation (p < 0.05) with Ni were observed in the mineral horizon. Organic transition metal complexation seems to play an important role in governing SOC in the mineral horizon. That is, the complexation maintains organic carbon stability, slows down its decomposition rate, and accumulates organic carbon. The Ca–SOC positive correlation in the mineral horizon exits because Ca also can complex with organic carbon. Co, Cu, and V–SOC positive correlations (p < 0.05) were also observed, but there were no significant positive correlations (p < 0.01) in the surface horizon because surface SOC had diversified sources. An SOC evolution model influenced by the bedrock was forwarded. Thus, the different soil geochemistry originating from different bedrocks should be noticed when SOC and global carbon cycles are discussed.

Impact of Technogenic Saline Soils on Some Chemical Properties and on the Activity of Selected Enzymes

The study was based on saline soils with surface mineral layers impacted by the waste produced by the soda plant in Poland. The activity of selected enzymes (catalase CAT, alkaline AlP, and acid phosphatase AcP), pH in KCl, content of the clay, total organic carbon (TOC), total nitrogen (TN), total exchangeable bases (TEB), electrical conductivity (ECe), CaCO3, and concentration of available phosphorus AP were investigated in the soil next to the soda plant. Based on the enzyme activity, the following were calculated: enzymatic pH indicator AlP/AcP, the resistance index (RS), resilience index (RL), relative changes (RCh), and the time index (TI). The soil was sampled from the mineral horizon in spring and autumn from eight (S1–S8) soil sampling sites in the area of the soda plant and from the control point (C). Soil is characterized by alkaline reaction. Statistical analysis (ANOVA, η2 effect size) showed significant variation in parameters under the influence of different sites next to soda plant. The content of TOC ranged from 4.70 to 47.7 g kg−1, and TN from 19 to 4.36 g kg−1. ECe next to the soda plant ranged between 6.87 and 204 mS cm−1. The highest values were confirmed in the soil of S1 both in spring and autumn. Higher TEB values were noted in the soil in autumn. In the soil within the impact of the soda plant, the AP content decreased and in the soil from sites S1, S3, S6, and S8 (in spring), the lowest AP content was recorded at 1.20, 4.14, 5.98, and 0.99 mg kg−1, respectively. The highest activity of AlP in spring was noted at site S1 and in autumn at site S4. In the soil next to the soda plant, the activity of AcP decreased, as compared to the control which is seen from the negative values of the coefficient of relative changes (RCh). The analysis of RCh in the catalase activities showed that in the soil from sites S1, S2, S3, S4, and S5, the activity increased, as compared to the control. The lowest values of the resistance index (RS) for phosphatases were reported in the soil of S6. Research shows that the activity of enzymes and their indexes make it possible to conduct long-term monitoring and identify the processes in soil.

Bacterial Number and Genetic Diversity in a Permafrost Peatland (Western Siberia): Testing a Link with Organic Matter Quality and Elementary Composition of a Peat Soil Profile

Permafrost peatlands, containing a sizable amount of soil organic carbon (OC), play a pivotal role in soil (peat) OC transformation into soluble and volatile forms and greatly contribute to overall natural CO2 and CH4 emissions to the atmosphere under ongoing permafrost thaw and soil OC degradation. Peat microorganisms are largely responsible for the processing of this OC, yet coupled studies of chemical and bacterial parameters in permafrost peatlands are rather limited and geographically biased. Towards testing the possible impact of peat and peat pore water chemical composition on microbial population and diversity, here we present results of a preliminary study of the western Siberia permafrost peatland discontinuous permafrost zone. The quantitative evaluation of microorganisms and determination of microbial diversity along a 100 cm thick peat soil column, which included thawed and frozen peat and bottom mineral horizon, was performed by RT-PCR and 16S rRNA gene-based metagenomic analysis, respectively. Bacteria (mainly Proteobacteria, Acidobacteria, Actinobacteria) strongly dominated the microbial diversity (99% sequences), with a negligible proportion of archaea (0.3–0.5%). There was a systematic evolution of main taxa according to depth, with a maximum of 65% (Acidobacteria) encountered in the active layer, or permafrost boundary (50–60 cm). We also measured C, N, nutrients and ~50 major and trace elements in peat (19 samples) as well as its pore water and dispersed ice (10 samples), sampled over the same core, and we analyzed organic matter quality in six organic and one mineral horizon of this core. Using multiparametric statistics (PCA), we tested the links between the total microbial number and 16S rRNA diversity and chemical composition of both the solid and fluid phase harboring the microorganisms. Under climate warming and permafrost thaw, one can expect a downward movement of the layer of maximal genetic diversity following the active layer thickening. Given a one to two orders of magnitude higher microbial number in the upper (thawed) layers compared to bottom (frozen) layers, an additional 50 cm of peat thawing in western Siberia may sizably increase the total microbial population and biodiversity of active cells.

Value added? Comparative estimates of peat basin volumetrics using borehole methods and 3D ground-penetrating radar

<p>Peatlands have long been recognized as providing a wide range of ecosystem services valuable to humans. In recent decades their role in the global climate and particularly their importance in long-term carbon sequestration has come into focus. Peatlands and peat basins are an important carbon store globally, and are estimated to cover nearly 25% of the Scottish landscape: they constitute a significant carbon stock, but being able to accurately estimate the volume of peat stored in coastal basins, both locally and regionally, remains a time-consuming process. Traditional methods of investigating peat depth and volume involved the measurement of peat to depth of contact with a mineral horizon, such as sand. This process is conducted with a peat depth probe or corer, with the spatial density of measurements varying significantly with basin size. Volumetric assessments based on such measurements therefore require interpolation between control points, leading to unquantifiable errors particularly if the base of peat has significant and unrecorded topography. Geophysical methods, in particular the 3D application of ground-penetrating (GPR), offer a promising solution to improve the accuracy in basin volumetrics.</p><p>In this paper, a 3D dataset of 100 MHz GPR data was acquired with a Mala Geosciences Rough Terrain system over a buried Holocene coastal environment near Arisaig, northwest Scotland. 3D surveying involves the acquisition of a suite of parallel GPR profiles, with a small profile separation to capture the full variability of subsurface structure. For this site, a profile was acquired every 0.5 m, over an area of 62 x 32 m.  The site is also sampled by 39 boreholes, which record the base of peat between 1-3.2 m depth and indicate a peat volume of 3720 m<sup>3</sup>. By revealing the true topography of the base of the basin, the GPR data suggest that the borehole-derived volume is overestimated by almost 50%, and instead predict a basin volume of 2529 ± 200 m<sup>3</sup>. Of this, 2064 ± 200 m<sup>3 </sup>is classified as organic peat (81.6%) and the remaining 465 ± 200 m<sup>3 </sup>is marine clay (18.4%).  The principal source of error in this estimate is in the constraint of the GPR velocity, required to convert the time-axis of the GPR dataset to depth. This was measured at 0.034 m/ns ± 8%.</p><p>The acquisition of 3D GPR data is nonetheless time-consuming and requires precise positional control to locate the GPR antennas and avoid misinterpretation. Nonetheless, sufficient topographic information is captured even if the acquisition had recorded only every 5<sup>th</sup> GPR profile: for this downsampled dataset, the estimated basin volume is 2490 m<sup>3 </sup>± 200 m<sup>3</sup> (a difference of only 2.5% from the full 3D dataset). 3D survey methods, therefore, give confidence to a volumetric estimate, but the need for full-resolution 3D sampling can likely be relaxed. However, GPR surveys reveal subsurface variability that would be difficult to reconstruct from a sparse set of borehole observations. Nonetheless, some amount of borehole control is invaluable for validating the GPR data and providing ground-truth control of subsurface structure.</p>

Stand species composition as a key factor determining the amount of polycyclic aromatic hydrocarbons (PAHs) in forest soils

The aim of the study was to determine the effect of stand species composition on PAHs accumulation. The study covered the soils of the stands of the Rybnik Forest District, which are under the influence of one of the highest deposition of industrial emissions in Europe. Pine, pine-oak and oak stands growing in the same soil conditions were selected for the study. Samples for further analyses were collected from the organic horizon, from the humus mineral horizon and from the mineral horizon. Organic C content, N content, pH, alkaline cation content, as well as microbiological biomass of C, N, extracellular and intracellular enzyme activity were determined in the soil samples. PAH content was determined in the soil samples. Additionally, the soil organic matter fractions were determined: free light fraction (fLF), occluded light fraction (oLF) and mineral associated fraction (MAF). Pine stand soils were characterized by the highest average PAHs content. The oak stand soils were characterized by the lowest PAHs accumulation and high enzymatic activity. The study confirms the important role of the stand species composition in shaping the quality and quantity of SOM and soil acidification, which in turn is reflected in microbial activity and PAHs accumulation in forest soils. PAHs accumulation in forest soils is related to the fractional composition of SOM, which is the effect of the influence of species composition through the supplied aboveground and belowground biomass. A strong correlation between the PAH content and C content of the light soil fraction of OM was noted.

Caractéristiques morpho-pédologiques et potentialités agricoles de sols développés sur roches dolomitiques dans le bassin de Taoudéni au Burkina Faso

Dans l’Ouest du Burkina Faso ont été identifiés des sols développés sur des dolomies. L’absence d’étude pédologique antérieure dans la région, traitant de l’implication géochimique des roches dolomitiques sur les propriétés de ces sols, a conduit à la réalisation d’une étude morpho-pédologique. Celle-ci avait pour objectif d’évaluer l’impact des carbonates sur les caractéristiques morphologiques, physiques, chimiques et hydriques des sols en vue d’en dégager les potentialités. Cette prospection menée à partir de trois transects, partant chacun des trois principales collines dolomitiques de la région (Diounkan, Souroukoudinga et Samendéni) indique l’existence d’argiles de type 2/1. Ces argiles interviennent positivement dans la structuration des sols, la rétention de l’eau et des nutriments grâce à leur CEC élevée comprise entre 11 et 20 cmol(+).kg-1. On note, par ailleurs, un déséquilibre cationique entre Ca2+et Mg2+, car le ratio Ca2+/Mg2+>1 dans l’horizon organo-minéral, devient < 1 en profondeur, traduisant ainsi un excès de Mg2+ à ce niveau. Les rapports Mg2+/K+ et Ca2+/K+ parfois > 50 et le ratio K+/CEC < 0,05, indiquent une carence en K+. Par conséquent, le potassium pourrait constituer, avec le phosphore (< 5 mg.kg-1), les principaux facteurs limitant la productivité des sols. L’utilisation durable de ces sols exige un choix judicieux des types de cultures et un mode de fertilisation organo-minérale pour compenser les carences. Mots clés: Argiles, cations, antagonisme potassium-magnésium, fertilité du sol, roches dolomitiques. English Title: Morpho-pedological characteristics and agricultural potentialities of soils developed on dolomitic rocks in the Taoudeni basin in Burkina FasoIn western of Burkina Faso, soils developed on dolostones have been identified. Lack of previous soil study in the region, dealing with the geochemical implication of dolomitic rocks on the properties of these soils, led to the realization of a morpho-pedological study. The purpose of this study was to assess the impact of carbonates on the morphological, physical, chemical and water characteristics of the soils in order to identify their potential. This prospecting carried out starting from three transects, starting each from the three main dolomitic hills of the region (Diounkan, Souroukoudinga and Samendeni) indicates the existence of type 2/1 clays. These clays play a positive role in the structuring of soils, the retention of water and nutrients thanks to their high CEC between 11 and 20 cmol(+)kg-1. There is also a cationic imbalance between Ca2+ and Mg2+, because Ca2+/Mg2+ > 1 ratio in the organo-mineral horizon becomes < 1 from the median horizon, thus reflecting an excess of Mg2+ at this level. The Mg2+/K+ and Ca2+/K+ ratios sometimes > 50 and the K+/CEC ratio < 0.05 indicate a deficiency of K+. Consequently, potassium could constitute with phosphorus (<5 mg.kg-1) the main factors limiting the productivity of these soils. The sustainable use of these soils requires a judicious choice of crop types and an organo-mineral fertilization method to compensate for the deficiencies. Keywords: Clay, cations, potassium-magnesium antagonism, soil fertility, dolostones.

Hydrological conditions and peat constitution effect on DOC leaching from permafrost-affected soils: model experiment (Western Siberia, Russia)

&lt;p&gt;In the northern ecosystems&amp;#8217; soils, the carbon stock is preserved in peat soils which includes frozen peat. It is vulnerable to any climate changes. The permafrost degradation can affect both the quantity and the composition of dissolved organic carbon of permafrost-affected soils, especially peat soils.&lt;/p&gt;&lt;p&gt;The main aim of our study was to determine the relationship among peat type, water regime and the quantity and composition of water borne carbon export. The research site was located in the discontinuous permafrost zone (N65&amp;#186;18&amp;#8217;, E72&amp;#186;52&amp;#8217;). Monoliths of various peat soils were collected in summer 2019 for a laboratory experiment.&lt;/p&gt;&lt;p&gt;The experiments were carried out with 6 types of monoliths (oligotrophic fibric peat; oligotrophic hemic peat with lichen debris; eutrophic hemic peat with reindeer moss debris; eutrophic sapric peat; eutrophic sapric peat with a burnt horizon; oligotrophic fibric peat, underlied with sand). We try to understand how organic matter is leached from peat soils with different constitution and different degree of decomposition. In the model experiment, we simulated 3 types of hydrological conditions. Soil monoliths were watered, and the contents of DOC and POC were determined in the collected soil waters.&lt;/p&gt;&lt;ol&gt;&lt;li&gt;Simulation of the moderate rainfall (70 mm) by adding distilled water during the week. DOC in this case ranged from 44,2&amp;#177;3.0 mg/l in oligotrophic peat to 80,6&amp;#177;28,7 mg/l in eutrophic peat.&lt;/li&gt; &lt;li&gt;The simultaneous flow of large quantities of water, simulating prolonged rainfall or spring snowmelt. In this case DOC content leaching from fibric oligotrophic peat didn`t change much while DOC leaching from sapric eutrophic peat decreased in comparison with moderate rainfall.&lt;/li&gt; &lt;li&gt;During modeling short stagnant regimen (spring conditions) we observed increase DOC, especially in sapric eutrophic peat (up to 291,0&amp;#177;11,3 mg/l). The mineral horizon under the peat layer reduced the rate of leaching of organic substances from the soil.&lt;/li&gt; &lt;/ol&gt;&lt;p&gt;Our results indicate the significant role of both the peat constitution and hydrological regime of soils on the rate and amount of organic matter entering the hydrological basin from peat permafrost-affected soils. The data can be used to simulate the dynamics of permafrost ecosystems with changing climatic parameters or with the activation of anthropogenic load.&lt;/p&gt;&lt;p&gt;This research was supported by the Russian Foundation for Basic Research (Grant 18-04-00952)&lt;/p&gt;

Effects of magnesite fertilization on soil properties and nutrition state of weakened Norway Spruce stands in the Śnieżnik Massif of Polish Eastern Sudety Mountains

The aim of this study was to assess the effects of fertilization with magnesite, 6 years after its application. The magnesite fertilizer was applied in amount of 2,000 kg·ha-1 in 2006. Fertilization covers the surface of 43 ha. Soil exploration in fertilized and unfertilized areas was carried out in August 2012. Needles and soil samples were collected for basic laboratory analysis. The effect of magnesite fertilization in soil was detected down to the B horizon. The principal excess of exchangeable magnesium (88%) was found in the surface organic horizon, while a substantial excess of total magnesium (57%) was detected in the top mineral horizon. The fertilization with magnesite caused the decreasing: acidity, ratio of calcium to magnesium in the absorption complex, supply of calcium in soil. Additionally, an increased magnesium supply in soil and its effect in the needles of the investigated spruce stands were noted. Research study confirm the usefulness of ground magnesite in elimination the deficit of magnesium in soils and needles of spruce stands in the Śnieżnik Massif for an extended period of time. Fertilization with magnesite at low doses may bring beneficial and quick effects to the health condition and productivity of spruce stands growing on soils well supplied with nitrogen. Keywords: spruce stands decline; soil properties; fertilization with magnesite, spruce nutrition status.

Proteolytic Activity in Meadow Soil after the Application of Phytohormones

Phytohormones, similar to soil enzymes, are synthesized and secreted into the soil environment by fungi and microorganisms. Phytohormones are involved in regulating microbial community activity in the rhizosphere. This paper examines how auxins, cytokinins, ethephon and chlorocholine chloride affect the activity of native soil proteases in the organo-mineral horizon of an alpine meadow. In the meadow habitat, native soil proteases were inhibited by auxins whereas the effect of cytokinins on these enzymes was not statistically significant. A similar inhibitory effect on the activity of proteases was shown for ethephon and chlorocholine chloride, both of which also inhibited the activity of native soil proteases in the alpine meadow soil. Overall, the inhibitory effect of phytohormones on the activity of native protease activity may affect plant nutrition by retarding the nitrogen cycle in the soil. This work contributes to our understanding of the influence of substances produced by the rhizosphere that can actively participate in the activity of soil microorganisms and consequently influence the soil nitrogen cycle.

Present soils and past land use: the “bracken economy” in Lea-Artibai County (Basque Country, northern Spain) in the late nineteenth and early twentieth centuries

Soils in Lea-Artibai County (northern Spain) show three significant features: frequent absence of A horizons, higher nutrient concentrations in the surface mineral horizon of past or present arable fields compared to those in forest or shrubland, and the common presence of calcareous horizons in arable fields which is out of character with the region’s humid climate. Farmers stopped applying lime around 1950, so the third feature is interpreted as the result of over-liming since the eighteenth century. The “maize revolution” that began in the mid-seventeenth century relied upon a three-crop rotation system using bracken as a primary fertilizer along with animal manure and lime obtained from local kilns that burned gorse. Extraction of these plant materials resulted in a negative phosphorus balance of phosphorus and the acidification of shrubland soils. The county could not accommodate these various land uses in the early twentieth century, and extraction of leaf litter from forests and shrublands became necessary. In the “concentrational agriculture” of the maize revolution, organic matter and nutrients accumulated in arable fields and diverted ecological pressure onto shrubland and forest soils, creating a “metabolic rift” that is still evident in the soils of Lea-Artibai County.