Non-cultivated Soils Research Articles

Actinobacteria Structure in Autogenic, Hydrogenic and Lithogenic Cultivated and Non-Cultivated Soils: A Culture-Independent Approach

The aim of the study was to determine the Actinobacteria structure in cultivated (C) versus non-cultivated (NC) soils divided into three groups (autogenic, hydrogenic, lithogenic) with consideration its formation process in order to assess the Actinobacteria sensitivity to agricultural soil use and soil genesis and to identify factors affecting their abundance. Sixteen C soil samples and sixteen NC samples serving as controls were taken for the study. Next generation sequencing (NGS) of the 16S rRNA metagenomic amplicons (Ion Torrent™ technology) and Denaturing Gradient Gel Electrophoresis (DGGE) were applied for precise determination of biodiversity. Generally, greater abundance of Actinobacteria in the NC soils relative to the C soils was found. Moreover, it was indicated that the actinobacterial diversity depended on both the soil genesis and the land use; however, this effect directly depended on the particular family and genera. Two factors: redox potential (Eh) and total carbon (TC) seemed to had a significant effect on the diversity of Actinobacteria. More precisely, Actinobacteria from the NC soils displayed a greater affinity for each other and were clearly influenced by Eh, whilst those from the C soils were mostly influenced by TC.

Particulate Organic Matter in Noncultivated and Arable Soils

Data on the contents of particulate organic matter (POM) in the humus horizons of different soil types were obtained. The influence of the land use system and fertilizers on the carbon of particulate organic matter (CPOM) in gray forest soil and typical chernozem was shown. The mineralization rate of POM under constant conditions of temperature and moisture was estimated, and the ratios between the pools of POM and biologically active organic matter in the soils were calculated. In the soils of natural cenoses, the percentage of POM together with the sand particle-size fraction varied within 12–36% of the soil mass, and the CPOM content varied from 1.66 to 8.03% of the fraction mass. The portion of CPOM in the total Corg ranged from 20 to 48%. Cultivated gray forest soil and typical chernozem were depleted of CPOM by 3.0–3.2 and 2.0–2.8 times, respectively, in comparison with the samples of noncultivated soils. The mineralization rate of POM in the gray forest soil and typical chernozem was about the same (7.9–12.1 and 7.2–8.2% of CPOM, respectively), which was about 1.2–2.4 times higher than the mineralization rate of the total soil organic matter. It was noted that POM could be a sensitive indicator of the Corg dynamics in the soil, a good predictor of changes in the content and quality of soil organic matter, and a significant source of potentially mineralizable organic matter in the soil.

Distribution of Entomopathogenic Fungi in Cultivated and Noncultivated Soils in Southern Tamaulipas, Mexico

Distribution of Entomopathogenic Fungi in Cultivated and Noncultivated Soils in Southern Tamaulipas, Mexico

Crop-weed competition changes the decomposition of soil organic matter fractions in the rhizosphere

ABSTRACTCertain plant combinations can stimulate the mineralization of soil organic matter (SOM), thereby changing the storage of soil organic carbon and affecting the physical and chemical soil properties. The aim of this study was to evaluate whether competition between weeds and maize can stimulate SOM decomposition. Eight treatments were performed: monoculture of maize and weeds (Amaranthus viridis, Bidens pilosa, and Ipomoea grandifolia), maize in competition with weeds, and non-cultivated soil. During cultivation, the rhizosphere priming effect (RPE) on SOM was estimated. Additionally, at 60 days after planting, soil samples were collected to measure the C contents of particulate (POM) and mineral-associated (MAOM) organic matter. From the 43rd day of cultivation onwards, the coexistence between maize and B. pilosa led to the highest RPE values, while maize vs. A. viridis showed negative RPE. Maize vs. A. viridis and maize vs. I. grandifolia caused increase in MAOM-C and decreases in POM-C. Ipomoea grandifolia monoculture and maize vs. B. pilosa led to the highest MAOM-C losses and reduced POM-C compared to the non-cultivated soils. Here it is demonstrated that competition between maize and B. pilosa increases SOM mineralization, while competition between maize and A. viridis or I. grandifolia retards this process.

Suppression of arbuscular mycorrhizal fungal activity in a diverse collection of non-cultivated soils.

Most plants form symbiotic associations with arbuscular mycorrhizal fungi (AMF). AMF increase the uptake of plant nutrients by extending their extra-radical mycelium (ERM) in the soil where other groups of microorganisms may suppress the activity of the ERM. However, little is known about such suppression in natural soils. This work aimed to investigate the incidence of AMF suppression among soils sampled from highly variable natural ecosystems, and used 33P uptake by the ERM to evaluate AMF activity. A second aim was to identify factors behind the observed AMF-suppression. We found that AMF-suppressiveness varied markedly among natural soils and occurred more frequently in low pH than in high pH soils. A previous study for cultivated soils revealed a strong biological component of suppressiveness against AMF, and in accordance we found that the composition of both fungal and bacterial communities differed significantly between AMF-suppressive and non-suppressive natural soils. Acidobacteria, Acidothermus, Xanthomonadaceae, Archaeorhizomyces sp., Mortierella humilis and some Mycena spp. were significantly more abundant in AMF-suppressive soils and may therefore be direct antagonists of AMF. This implies that the functioning of AMF in natural ecosystems is strongly modulated by specific soil microbes.

Effect of Compost and Biochar on Heavy Metals Phytostabilization by the Halophytic Plant Old Man Saltbush [Atriplex Nummularia Lindl

ABSTRACTRemediation of soils is vital to mitigate the negative effects of heavy metals in ecosystems. There is little information available about the metals’ phytostabilization potential of old man saltbush plants [Atriplex nummularia]. A pot experiment in a randomized complete block design was conducted to study the accumulation of heavy metals by old man saltbush plants, as affected by the application of compost and biochar. The cultivation of A. nummularia is an effective tool in immobilizing metals in the contaminated soils. The cultivation of metal-contaminated soil with A. nummularia reduced the availability of Zn, Cu, Cd, and Pb by 20%, 4%, 21%, and 28%, respectively, in comparison to the non-cultivated soil. Zn, Cu, Cd, and Pb concentrations in the aboveground parts of old man saltbush plants were 70–100, 50–80, 4–5, and 50–90 mg/kg of dry biomass. The higher Zn, Cu, Cd, and Pb concentrations were accumulated in the roots, and the lower concentrations were transferred to the shoots of old man saltbush plants. Compost reduced the concentration of Zn, Cu, Cd, and Pb in the shoots by 10%, 19%, 20%, and 6%, respectively, compared to the control soil. Biochar reduced the concentrations of Zn, Cu, and Pb in the shoots by 30%, 38%, and 44%, respectively, compared to the control. Compost had a lower effect in reducing the metals uptake as biochar. Biochar reduced the uptake of Zn, Cu, and Pb in the shoots of the tested plant by 22%, 23%, and 41%, respectively, in comparison to compost. Based on the obtained results, old man saltbush has good characteristics to be a promising candidate for phytostabilization strategies of metal-contaminated soils. Moreover, biochar is a good tool to enhance metals’ phytostablization.

Effects of Agricultural Activities on Soil Mercury Changes in the Water-Level-Fluctuating Zone of the Three Gorges Reservoir

Farming in the water-level-fluctuating zone (WLFZ) of the Three Gorges reservoir, China, may result in a wide range of environment problems when the sediment is exposed to air. In this study, Qukou, Chongqing, was selected as the research site due to its large WLFZ area and significant agricultural activities. Four kinds of land use types, including rice, maize, vegetables, and grassland, were selected to investigate the distribution of mercury (Hg) in the surface soil. The results showed that the mean concentrations of soil total Hg (THg), bioavailable Hg (Hg-wh), and methylmercury (MeHg) in the surface soil were 25.80-68.74 ng ·g-1, 0.44-0.88 ng ·g-1, and 0.08-0.85 ng ·g-1, respectively. The concentrations of THg, Hg-wh, and MeHg in non-cultivated soil were higher than those in cultivated soil, indicating that farming disturbances could accelerate soil Hg loss. The MeHg concentrations in both non-cultivated and cultivated soil increased up to the maximum value 1-2 months after drying, and then gradually decreased to a relatively stable level. The peak value was approximately four times higher than that at the end of flooding. The percentage of MeHg to THg (% MeHg) was similar to the distribution of soil MeHg, and the peak value occurred at 1 month after drying. However, when% MeHg decreased to the stable level, no significant difference was found compared to the value at the end of flooding (P>0.05). Furthermore, the soil% MeHg had a significantly positive correlation with Hg-wh (r=0.642, P<0.01), while there was no significant correlation with THg (P>0.05), suggesting that Hg methylation was mainly affected by the bioavailability of Hg in the seasonally inundated soil of the WLFZ.

Stability and patterns of topsoil water content in rainfed vineyards, olive groves, and cereal fields under different soil and tillage conditions

Topsoil water content (TSWC) varies at spatial and temporal scales owing to the influence of several factors. In woody crops, few studies have analysed these dynamics under rainfed conditions. The temporal stability of the spatial patterns of TSWC in a Mediterranean rainfed sub-catchment (27 ha; Spain) was analysed during 12 months. Cropland includes four vineyards with cover crops, five cereal fields (fallow/crop rotation), one olive grove under conventional tillage, and one abandoned olive grove. In total, nine land use compartments were distinguished in twelve fields and nine non-cultivated soils. During the test period (May 2016–April 2017) the monthly TSWC values (mean 13.1% vol. ±8.0) showed a significant correlation with evapotranspiration. The spatial variability of TSWC increased under dry conditions and more homogeneous patterns appeared in the wet surveys. The vineyards’ inter-rows had the wettest (62% > in the rows) conditions owing to the cover crops and their high soil-water holding capacity, and average temporal stability. The vineyards’ rows were dry and very stable due to the tillage practices (higher elevation) and the low infiltration rates; and the corridors had wet and stable conditions. The forest presented the driest and stable temporal conditions associated to the water demand by the trees. Soil in the fallow cereal fields was drier and more stable than in the cereal fields. The abandoned olive grove showed wetter though less stable conditions than the olive grove. The trails had wet but not stable conditions. The different land uses and tillage practices influenced more the TSWC dynamics than the spatial variability of the analysed soil physical properties. However, silty loam and loamy soils presented wetter and more stable conditions than the average values, and the sandy loam and loamy sand soils had drier and less stable conditions.

Rare earth elements profile in a cultivated and non-cultivated soil determined by laser ablation-inductively coupled plasma mass spectrometry

Rare earth elements (REEs) have several applications but the effects on environment are not well known. Therefore, the aim of this work is to establish a method for direct solid sample analysis by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) to evaluate the concentration and distribution of REEs in cultivated and non-cultivated soil. Samples were collected in two areas to 40 cm of depth. The LA-ICP-MS method is easy to be implemented and the sample treatment is very fast comprising only its drying, grounding and pressing as a pellet. The accuracy of the method was evaluated by using a certified reference material (BCR 667 – Estuarine Sediment, Institute for Reference Materials and Measurements (IRMM)) where good agreement with the certified values was obtained. Analyte recovery at two levels of concentration (2.5 and 15.0 μg g−1) was also performed and recoveries in the range of 85%–120% were achieved, values that are acceptable for LA-ICP-MS analysis. In general, the concentration of the REEs is higher in the cultivated soil and increased from the surface to deeper layers, which can be a consequence of fertilizer application.

Easily degradable carbon – an indicator of microbial hotspots and soil degradation

AbstractThe effect of arable soil was quantified against non-cultivated soil on easily degradable carbon and other selected microbiological factors,i.e.soil microbial biomass, respiration activity, and dehydrogenase activity. The intent was to ascertain whether easily degradable carbo can be useful as a sensitive indicator of both soil biological degradation and microbial hot-spots indication. As a result, it was found that soil respiration activity was significantly higher (p &lt;0.0001) in all controls, ranging between 30-60vs.11.5-23.7 μmol CO2kg d.m.−1 h−1for the arable soils. Dehydrogenase activity was significantly lower in the arable soil (down to 35-40% of the control values, p &lt;0.001) varying depending on the soil type. The microbial biomass was also significantly higher at the non-cultivated soil (512-2807vs. 416-1429 µg g−1d.m., p &lt;0.001), while easily degradable carbon ranged between 620-1209 mg kg−1non-cultivated soil and 497-877 mg kg−1arable soil (p &lt;0.0001). It was demonstrated that agricultural practices affected soil properties by significantly reducing the levels of the studied parameters in relation to the control soils. The significant correlations of easily degradable carbon-respiration activity (ρ= 0.77*), easily degradable carbon-dehydrogenase activity (ρ= 0.42*), and easily degradable carbon-microbial biomass (ρ= 0.53*) reveal that easily degradable carbon is a novel, suitable factor indicative of soil biological degradation. It, therefore, could be used for evaluating the degree of soil degradation and for choosing a proper management procedure.

Aspergillus section Flavi community structure in Zambia influences aflatoxin contamination of maize and groundnut

Aflatoxins are cancer-causing, immuno-suppressive mycotoxins that frequently contaminate important staples in Zambia including maize and groundnut. Several species within Aspergillus section Flavi have been implicated as causal agents of aflatoxin contamination in Africa. However, Aspergillus populations associated with aflatoxin contamination in Zambia have not been adequately detailed. Most of Zambia's arable land is non-cultivated and Aspergillus communities in crops may originate in non-cultivated soil. However, relationships between Aspergillus populations on crops and those resident in non-cultivated soils have not been explored. Because characterization of similar fungal populations outside of Zambia have resulted in strategies to prevent aflatoxins, the current study sought to improve understanding of fungal communities in cultivated and non-cultivated soils and in crops. Crops (n=412) and soils from cultivated (n=160) and non-cultivated land (n=60) were assayed for Aspergillus section Flavi from 2012 to 2016. The L-strain morphotype of Aspergillus flavus and A. parasiticus were dominant on maize and groundnut (60% and 42% of Aspergillus section Flavi, respectively). Incidences of A. flavus L-morphotype were negatively correlated with aflatoxin in groundnut (log y=2.4990935−0.09966x, R2=0.79, P=0.001) but not in maize. Incidences of A. parasiticus partially explained groundnut aflatoxin concentrations in all agroecologies and maize aflatoxin in agroecology III (log y=0.1956034+0.510379x, R2=0.57, P<0.001) supporting A. parasiticus as the dominant etiologic agent of aflatoxin contamination in Zambia. Communities in both non-cultivated and cultivated soils were dominated by A. parasiticus (69% and 58%, respectively). Aspergillus parasiticus from cultivated and non-cultivated land produced statistically similar concentrations of aflatoxins. Aflatoxin-producers causing contamination of crops in Zambia may be native and, originate from non-cultivated areas, and not be introduced with non-native crops such as maize and groundnut. Non-cultivated land may be an important reservoir from which aflatoxin-producers are repeatedly introduced to cultivated areas. The potential of atoxigenic members of the A. flavus-L morphotype for management of aflatoxin in Zambia is also suggested. Characterization of the causal agents of aflatoxin contamination in agroecologies across Zambia gives support for modifying fungal community structure to reduce the aflatoxin-producing potential.

Nitrous oxide emission after the addition of organic residues on soil surface

Abstract The addition of organic amendments with a low Carbon:Nitrogen (C:N) ratio to restore degraded soils may increase the emission of greenhouse gases and affect the storage of these elements in the topsoil. Our objectives were to evaluate the effect of the addition to the surface of organic amendments to a non-tilled and non-cultivated soil, compared with the addition of cover crop residues, with respect to: (i) N 2 O emissions and their relationships with soil variables, (ii) C and N content in the topsoil. We conducted an experiment during two consecutive years in Parana, Argentina (−31° 50.9′ S; −60°32.3′ W). Treatments included the addition of organic amendments (composted poultry litter and poultry manure) and cover crops residues [wheat ( Triticum aestivum L.) and white sweet clover ( Melilotus albus Medik.)]. Soil variables that are most commonly reported as critical for N 2 O emissions, i.e. soil nitrates (N-NO 3 ) and water filled pore space (WFPS), showed more differences among treatments in Year 1 than in Year 2, which was associated with a higher frequency and amount of rainfall. N 2 O flux ranged between 0.12–50 μg N m −2 d −1 (Year 1) and 0.62-13.7 μg N m −2 d −1 (Year 2). N 2 O flux was significantly associated with WFPS in both Years (P 3 (P 2 O emissions were extremely low, the highest values were recorded in poultry manure treatment, whereas, the lower values were recorded in crop residues and in the control treatment. Overall, our results suggest that the addition of organic amendments in our region, with a massive adoption of no-till, that were broadcasted before (i.e. 30–45 days) the sowing of summer crops, are associated with low N 2 O emissions and potential improvements in soil quality. In addition, the experimental approach allowed us to more clearly identify the drivers of N 2 O emissions and to better understand the soil processes that are involved in this particular situation, without the presence of a living vegetal cover.

Soil and Rhizosphere Bacterial Diversity in Maize Agro- Ecosystem

Management practices used in maize production have an impact on soil agro- ecosystems where different microbial communities coexist. Soil inhabiting bacteria are numerous and diverse, but we know very little about their ecological distribution. Here we analyzed the bacterial community diversity in the rhizosphere of two transgenic maize cultivars, in agricultural soil before sowing and in non-cultivated soil in an experimental site in the south region of Uruguay. We followed two culture-independent methods: DGGE (denaturing gradient gel electrophoresis) and 454-pyrosequencing of 16S rRNA gene amplicon. Through pyrosequencing, the three environments analyzed presented differences in terms of bacterial composition. However, no differences were found in the relative abundance of the ten most represented phyla in the rhizosphere of the two cultivars at different phenological stages. We found significant differences of Bacteroidetes, Gemmatimonadetes, Planctomycetes, Proteobacteria and Verrucomicrobia phyla when comparing agricultural and non-cultivated soils, as well as a significant enrichment of members of the phylum Gemmatimonadetes in all rhizosphere samples compared to soil. Through DGGE analysis we evidenced that maize rhizosphere bacterial communities changed at different phenological stages in both cultivars. We also provided baseline information about bacterial specific taxa within maize agro- ecosystem for further evaluation of possible rhizosphere bacterial community shifts of genetically modified maize cultivars under different management practices.

Using stable isotopes to explore root-microbe-mineral interactions in soil

The few millimeters of soil surrounding a plant's roots, the 'rhizosphere', are a nexus of biological activity, and inhabited by microorganisms that are critically important to both plant health and soil carbon (C) transformation and stabilization. Advancing our understanding of plant-microbe interactions and the soil carbon cycle requires disentangling the complex relationships among roots, soil microbes, mycorrhizae, and soil mineral surfaces. Yet in wildland systems, many important mechanistic rhizosphere questions remain unanswered. For example, most root C is decomposed to CO2, but of the remainder, what microbial transformations lead to the opportunity to become stabilized? How do plant species and microbial functionality regulate flows of C and nutrients, and how much do these vary over space and time? Transfer of root carbon to bacterial and fungal cell biomass may be a particularly important activity that precedes C stabilization on mineral surfaces, but the steps involved in this process remain ambiguous. In the past decade, multiple 'isotope-enabled' approaches have been developed that allow us to see and measure these complex rhizosphere interactions with high spatial, chemical, and molecular resolution. Here we present illustrative examples of these approaches as applied in non-cultivated soil systems.

Microbial biodiversity in arable soils is affected by agricultural practices

Abstract The aim of the study was to examine the differences in microbial community structure as a result of agricultural practices. Sixteen samples of cultivated and the same number of non-cultivated soils were selected. Gel bands were identified using the GelCompar software to create the presence-absence matrix, where each band represented a bacterial operational taxonomic unit. The data were used for principal-component analysis and additionally, the Shannon- Weaver index of general diversity, Simpson index of dominance and Simpson index of diversity were calculated. Denaturing gradient gel electrophoresis profiles clearly indicated differentiation of tested samples into two clusters: cultivated and non-cultivated soils. Greater numbers of dominant operational taxonomic units (65) in non-cultivated soils were noted compared to cultivated soils (47 operational taxonomic units). This implies that there was a reduction of dominant bacterial operational taxonomic units by nearly 30% in cultivated soils. Simpson dominance index expressing the number of species weighted by their abundance amounted to 1.22 in cultivated soils, whereas a 3-fold higher value (3.38) was observed in non-cultivated soils. Land-use practices seemed to be a important factors affected on biodiversity, because more than soil type determined the clustering into groups.

Urochloa decumbens growth and P uptake as affected by long-term phosphate fertilization, mycorrhizal inoculation and historical land use in contrasting Oxisols of the Brazilian Cerrado

ABSTRACT In the fertility management of highly weathered-leached Brazilian Oxisols, P is the most limiting macronutrient. A greenhouse experiment was conducted with the objective to evaluate the influence of the interaction between P doses, mycorrhizal inoculation and historical land use on Urochloa decumbens growth and P uptake in four Oxisols with contrasting chemical, physical and mineralogical properties. The plants were cultivated in plastic pots containing 4 kg of soil in a completely randomized design, four replications and 2x2x2 factorial scheme: with two P doses; with and without mycorrhizal inoculation; soils cultivated for long periods and non-cultivated (under native vegetation). There were two plantings of ten weeks each. Shoot dry mater, concentration and accumulation of P in the shoot were evaluated. In the first planting, the Urochloa response was greater in non-cultivated soils associated with inoculation and P addition. However, in the second planting, the inoculation had a greater effect in all soils compared to the first planting associated with the lowest P dose. As the P concentration in the soil increased, P in the shoot dry matter increases. The inoculation did not affect the P concentration and accumulation in the shoot of Urochloa. The growth of Urochloa decumbens was strongly influenced by the interaction among soil class x history of land use x dose of P x inoculation.

Soil chemical management drives structural degradation of Oxisols under a no-till cropping system

Physical degradation of the subsurface layer of soils reduces the effectiveness of no-till (NT) as a sustainable soil management approach in crop production. Chemical factors may reduce the structural stability of Oxisols and thereby exacerbate compaction from machinery traffic. We studied the relationship between chemical management and structural degradation in Oxisols cultivated under NT at three sites in southern Brazil. The surface and subsurface layers of the soils were characterised chemically and mineralogically and three physical attributes related to soil structural stability (readily dispersible clay in water, mechanically dispersible clay in water, and water percolation) were quantified for each layer. The same characterisations were performed on Oxisols collected from adjacent non-cultivated areas, to provide reference data for non-degraded soil. The levels of dispersed clay in the cultivated soil from the surface layer matched those of the non-cultivated soil, but for the subsurface layer higher dispersed clay levels in the cultivated soil showed that it was physically degraded relative to the non-cultivated soil. Water percolation was found to be slower through the Oxisols cultivated under NT, irrespective of the soil layer. The relationships between the three indicators of soil structural stability and the measured chemical and mineralogical variables of the soils were explored through an analysis of canonical correlation. The principal variables associated with the lower stability of the cultivated vs non-cultivated Oxisols were the lower concentrations of organic carbon and exchangeable aluminium and, for the surface layer, the higher pH. It is argued that structural degradation of Oxisols cultivated under NT, observed predominantly in the subsurface layer, has been aggravated by the accumulation of amendments and fertilisers in the surface soil and reduced levels of organic matter, especially in the subsurface layer.

Characteristics of Phosphorus Adsorption of Acidic, Calcareous, and Plastic Film House Soils

Continuous excessive application of phosphorus (P) fertilizer and manure in plastic film house soils can lead to an accumulation of P in soils. The understanding of P sorption by soils is important for fertilizer management. In this study, 9 samples were collected for acidic and calcareous soils as non-cultivated soil and plastic film house soils as cultivated soil Phosphorus sorption data of acidic soils fit the Langmuir equations, Freundlich equations in calcareous and plastic film house soils. In calcareous and plastic film house soils, the slope of isotherm adsorption changed abruptly, which could be caused P precipitation with <TEX>$CaCO_3$</TEX>. The calculated Langmuir adsorption maximum (<TEX>$S_{max}$</TEX>) varied from 217 to 1,250, 139 to 1,429, and <TEX>$714mg\;kg^{-1}$</TEX> for acidic soils, calcareous soils, and plastic film house soils with low available phosphate concentration, respectively. From this result, maximum P adsorption by the Langmuir equation could be regarded as threshold of P concentration to induce the phosphate precipitation in soil. Phosphate-sorption values estimated from one-point isotherm for acidic and calcareous soils as non-cultivated soils were comparable with the <TEX>$S_{max}$</TEX> values calculated from the Langmuir isotherm.

Atmospheric Deposition-Carried Zn and Cd from a Zinc Smelter and Their Effects on Soil Microflora as Revealed by 16S rDNA.

In this study, we investigated the influence of heavy metals (HM) on total soil bacterial population and its diversity pattern from 10 km distance of a Zinc smelter in Feng County, Qinling Mountain, China. We characterized and identified the bacterial community in a HM polluted soil using 16S rDNA technology. Out results indicated that the maximum soil HM concentration and the minimum bacterial population were observed in S2 soil, whereas bacterial diversity raised with the sampling distance increased. The bacterial communities were dominated by the phyla Proteobacteria, Acidobacteria and Actinobacteria in cornfield soils, except Fimicutes phylum which dominated in hilly area soil. The soil CEC, humic acid (HA)/fulvic acid (FA) and microbial OTUs increased with the sampling distance increased. Shewanella, Halomonas and Escherichia genera were highly tolerant to HM stress in both cultivated and non-cultivated soil. Finally, we found a consistent correlation of bacterial diversity with total HM and SOM along the sampling distance surrounding the zinc smelter, which could provide a new insight into the bacterial community-assisted and phytoremediation of HM contaminated soils.

The geochemistry of calcareous forest soils in Sulaimani Governorate, Kurdistan Region, Iraq

The properties of and processes in calcareous soils are important in the context of dryland soil management and moderation of atmospheric CO2 by carbonate weathering. This study was conducted to determine the major and trace elemental composition in soils of the Kurdistan region of Iraq, and their geochemical features. Soil samples were taken from seven pedons, five of them from forest soils and two others from non-cultivated soils. Selected physical properties, total concentrations of elements and mineralogical properties were determined on samples from each horizon. Weathering processes in the soils are characterised by loss of Ca, Sr and several trace elements, and accumulation of less mobile elements such as Zr, Ti, and Al. The progress of carbonate weathering was best expressed using Ba/Sr and Rb/Sr ratios. Principal components analysis confirmed that distinctive geochemical differences for two profiles (significantly higher Mg, Co, Cr, Mn, and Ni) were likely to represent control by parent material, a conclusion reinforced by both mineralogical differences and the location of profiles relative to surficial geology. The other main geochemical processes differentiating the pedons were chemical weathering of carbonates and accumulation of residual elements. Calculation of absolute mass flux (τ) values showed that, for some profiles, concentration of mobile elements such as Na and K by evapotranspiration was potentially important, despite evidence for clay eluviation in most profiles. Absolute loss of several elements was also correlated with increased weathering as measured by Ba/Sr ratios. None of the forest soils showed enrichment-depletion (τ) profiles for Fe or Al consistent with podzolisation. This study highlights useful geochemical approaches to understanding chemical weathering and pedogenesis in calcareous soil profiles.