Soil Parent Research Articles

Effect of production temperature and particle size of rice husk biochar on mercury immobilization and erosion prevention of a mercury contaminated soil

Mercury (Hg) contaminated soil is a potential hazardous material especially under soil erosion and surface runoff. This work aims to use rice husk biochar to immobilize Hg and prevent erosion, and find the optimal production temperature and particle size of the biochar. The biochars were produced at 300, 500, and 700 °C and sieved to three particle sizes ~20, < 2, and < 0.15 mm. They were applied to a Hg contaminated loamy sand (20.2 mg/kg) and undergone simulated rainfall erosion representing 7 years of heavy rain events in Beijing. All biochar amendments reduced the runoff volume by 5.1–15.4%. Hg amount in runoff were significantly reduced by 36.7–48.8% after the amendments of biochar. The Hg concentration of infiltration was reduced by biochar treatments except that produced at 300 °C, while its amount was increased due to larger infiltration volume. All biochar amendments significantly reduced soil loss in runoff by 43.5–77.2%. Hg was enriched in the sediments (39.7–46.8 mg/kg) compared with the parent soil (20.2 mg/kg) regardless of biochar treatment, but its bioavailability was low. Higher pyrolysis temperature of the rice husk biochars resulted in less runoff, more infiltration, and better erosion prevention, while the effect of biochar particle size is less significant.

Are fungus-growing termites super sediment-sorting insects of subtropical environments?

Fungus-growing termites have long been considered as ecosystem engineers for the modifications they make to the soil, through their ability to concentrate nutrients and create patches of fertile land. However, few studies have highlighted the degree to which, in building their mounds, they are able to modify the grain-size distributions of the sediments and soils in their surroundings. Therefore, the aim of this study is to document the potential impact of fungus-growing termites on sediment sorting of their environment. The assessment is based on comparisons between two different mounds and their associated control soils developed in contrasting grain-size settings, one on sand and the other on fine material (diatomite). The sedimentary modifications carried out by termites between these two parent materials and associated constructed mounds are addressed using techniques mostly based on grain-size distributions (performed with End-Member Mixing Analyses) and soil micromorphology. In order to conduct this investigation, two fungus-growing termites’ mounds were selected in the Chobe Enclave District, northern Botswana. The key questions of this study center on the capacity of fungus-growing termites to (i) adapt to any kind of parent material to build their mounds, and (ii) enrich or deplete this parent soil to meet their texture requirements in terms of mound stability and other mechanical properties to insure the success of the colony. This study demonstrated that fungus-growing termites assemble the mandatory texture required for the functions and properties of their mounds, whatever a given parent material, by selecting, transporting, and mixing the various grain sizes. To conclude, the sorting by fungus-growing termites must be considered when reconstructing paleoenvironment based on particle-size distributions.

Rehabilitation effects on gully sediment yields and vegetation in a savanna rangeland

AbstractGully rehabilitation can contribute to catchment management by stabilizing erosion and reducing downstream sediment yields, yet the globally observed responses are variable. Developing the technical basis for gully rehabilitation and establishing guidelines for application requires studies that evaluate individual rehabilitation measures in specific environments. An eight‐year field experiment was undertaken to evaluate sediment yield and vegetation responses to several gully rehabilitation measures. The rehabilitation measures aimed to reduce surface runoff into gully head cuts, trap sediment on gully floors and increase vegetation cover on gully walls and floors. The study occurred in a savanna rangeland in northeast Australia. Two gullies were subject to treatments while four gullies were monitored as untreated controls. A runoff diversion structure reduced headcut erosion from 4.3 to 1.2 m2 yr−1. Small porous check dams and cattle exclusion reduced gully total sediment yields by more than 80%, equivalent to a reduction of 0.3 to 2.4 t ha−1 yr−1, but only at catchment areas less than 10 ha. Fine sediment yields (silt and clay) were reduced by 7 and 19% from the two treated gullies, respectively. The porous check dam deposits contained a lower percentage of the fine fraction than the parent soil. Significant regeneration of gully floor vegetation occurred, associated with trapping of organic litter and fine sediment. Increases in vegetation cover and biomass were comprised of native perennial grasses, trees and shrubs. In variable climates, long‐term gully rehabilitation will progress during wetter periods, and regress during droughts. Understanding linkages between rehabilitation measures, their hydrologic, hydraulic and vegetation effects and gully sediment yields is important to defining the conditions for their success.

Changes of carbon-isotope ratios in soil organic matter relative to parent vegetation and site specificity

Investigating the correlation between biodiversity and ecosystem function in natural environments using carbon-isotope composition (δ13C) allows distinguishing the nutrient cycling pattern and anthropogenic effects incorporation in plants and soil processes. The mechanisms behind the isotopic composition of soil organic matter (SOM) and parent vegetation in relation to the context of site-specificity was approached in this work. Formation of SOM can be affected by the presence of a high concentration of heavy metals in soils. Still, no systematic studies were performed in most of the industrial sites to support this hypothesis. In order to explore this incomplete understood influence, investigation of carbon isotope signatures (d13C) variations in soil organic matter were performed in two industrial areas from Romania (Copșa Mică industrial platform and Baia Sprie mining zone). The current study, also, investigated the C:N ratio variation, as well as the influence of N speciation regarding d13C values of SOM. The decrease in C:N ratio indicated an increasing effect of the microbial products on SOM matter at increasing depth, for both regions, while an increase of the denitrification processes with depth was found for both areas. For the most appropriate depth (20-40 cm), the soil from Baia Sprie region was more enriched in 13C comparing with the soil from Copsa Mica region, and this higher isotope fractionation of SOM might be due to a higher carbon content, respectively a higher nitrogen content of Baia Sprie soil. It was concluded that the SOM of the surface soil in the two investigated regions has an 13C isotopic composition similar to the plant remains from which it was formed, offering an integrated value of plant material, time and the local origin and providing useful markers of tree isotopic composition.

Ecological and phytocoenotic features of the vegetation cover of the Beshpagir Heights (Stavropol Upland)

The authors have studied herbaceous communities in the steppe landscapes of the Beshpagir Heights and this paper presents the results of this study. The floristic and ecological structure of phytocoenoses on limestone outcrops of the parent rock is discussed. As a result of the research carried out in 20192020, 185 species of higher plants were identified in the modern flora of the studied steppes. There are descriptions of 16 accounting sites. A phytocoenotic table is presented, a characteristic of communities is given and their structure is described. The abundance of species and the distribution by relief elements and communities were determined by experts on the basis of field information. The features of communities and the reasons for their spatial differentiation are revealed. It has been suggested that the factors determining a diversity of steppe vegetation in the studied region should be the following ones: the degree of destruction of the parent rock and soil development, high insolation and low ecotope moisture. The steppe communities are distinguished by their species richness and are of significant conservation interest; they include such rare and endangered species as Psephellus annae, Stipa pulcherrima, S. pennata, Scabiosa isetensis, S. micrantha, Medicago cancellata, Astragalus bungeanus, A. pseudotataricus, A. calycinus, Iris pumila, I. notha, Erodium stevenii, Thymus daghestanicus, Gypsophila glomerata, Allium inaequale, etc. The authors have shown that the studied steppes are important for the preservation of the biological diversity of the region; habitats of rare species are of scientific importance. By this research the authors have tried to emphasize the regional specificity of the studied communities, due to the geographical, ecological-coenotic and historical features. The results obtained will make it possible to assess the real phytocoenotic diversity of the steppe complex of the region, as well as to update further work on the inventory and monographic generalization of vegetation materials of the Stavropol territory. The typology of steppe vegetation can be detailed in further work.

Application of recycled tire polymer fibers and glass fibers for clay reinforcement

Soil reinforcement with fibers is a simple, efficient and low-cost (especially by incorporating waste or recycled fibers) technique for enhancing mechanical characteristics of soft soils. This experimental study investigates the effects of recycled tire polymer fibers (RTPF) and glass fibers (GF) on enhancing the strength/deformation properties of clays. A series of compaction, unconfined compression and direct shear tests were performed on precisely prepared composite soils comprising clay, with different amounts (i.e. 0.5, 1.0 and 1.5%) of RTPF and GF having varying lengths (5 and 10 mm). Laboratory findings indicated that the composite soils have lower dry density and higher optimum moisture content as compared to the clay. Both unconfined compression and shear strength test results on composite soils implied that while adding fibers increased the materials’ ductility, there was an optimal percentage of fibers (0.5% for RTPF and 1.0% for GF) causing the highest strength gain, beyond which strength decreased. Concerning the shear strength parameters, i.e. cohesion intercept and internal friction angle, the fiber inclusion was particularly influential in increasing cohesion, whereas changes in internal friction angle were minimal. Moreover, the shorter fibers (5 mm) were generally more efficient in reinforcing the clay. The fiber improved composite soils have a better ductility and load-bearing capacity compared to parent soils that can be beneficial in the construction of pavement and railway substructure, liners, small fills/dikes, backfills around pipes, and slope protections.

Evaluation of Coir Geotextile Reinforcement for Low-Volume Roads

ABSTRACT Natural geotextiles play a vital role in the reinforcement and ground improvement of soft compressible soil to enhance soil strength and ensure stability. Of all the natural fibers, coir possesses high tearing strength even in very wet conditions. Hence, in this paper, the efficacy of coir geotextile in improving the functional performance of the pavement and enhancing the modulus of the subgrade soil has been investigated by visual examination and by conducting tests such as Benkelman Beam Deflection (BBD) test, geogauge and static plate load tests on the test sections constructed in the field. The obtained data reveals that the elastic modulus of the subgrade multiplies appreciably when it is reinforced with coir geotextile, thereby helping in increasing the service life of the pavement. Similar results are reflected in the pavement condition survey results as well. The improvement attained in the elastic modulus of the reinforced subgrades is 1.41 and 1.25 times of the elastic modulus of the parent soil, with coir geotextile of mass per unit being 740 g/m2 and 365 g/m2, respectively. The modified subgrade elastic modulus is given as input to the KENLAYER software and analyzed in order to prepare a design chart for coir geotextile reinforced low-volume roads.

Physiological and biomass partitioning shifts to water stress under distinct soil types in Populus deltoides saplings

Abstract Aims Although soil environments exist extensive heterogeneity for many plants with a wide range of distribution, researches about effects of soil conditions on plants’ tolerance and adaptation are particularly inadequate. In our study, the aims are to reveal physiological strategies of Populus deltoides against drought stress under different soil conditions and to select the most suitable soil type for P. deltoides plantation. Methods Under controlled conditions, we used P. deltoides as a model species to detect differences in gas exchange rate, antioxidative capacity, nitrogen metabolism and biomass accumulation and partitioning in response to drought stress under three mineral soil types with distinct physicochemical characters, i.e. red soil (RS), yellow soil (YS) and yellow-brown soil (BS). Important Findings Exposure to 25% of field water holding capacity in soil for 3 months had significantly decreased biomass of all organs, photosynthetic rate, enzyme activities related to N assimilation, but increased H2O2, malondialdehyde and content of both NO3− and NH4+, when P. deltoides was planted in both RS and YS. In contrast, under BS, there are slightly negative effects exerted by water deficit on total biomass, gas exchange rate, activities of enzymes related to nitrogen metabolism and membrane damage caused by reactive oxygen species, which can be associated with a consistent increase in superoxide dismutase, peroxidase and catalase, and a higher ratio of root mass to shoot mass. It is concluded that, such higher capacity in tolerance and adaptation against drought stress under BS relative to both RS and YS could be accounted for more sufficient nutrient provision in soil parental materials and better soil aeration conditions which play a vital role in plant acclimation to water shortage. Our study also revealed that, distribution areas of BS might be preferable for cultivation of P. deltoides, when compared with those of RS and YS.

Red Parent Soils Create Wetland Problems

CSA NewsVolume 65, Issue 8 p. 15-15 SOCIETY SCIENCE Red Parent Soils Create Wetland Problems First published: 16 July 2020 https://doi.org/10.1002/csan.20238Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume65, Issue8August 2020Pages 15-15 RelatedInformation

Chemical fractionation and mobility of nickel in soils in relation to parent materials

ABSTRACT Information on the various nickel (Ni) fractions and mobility in soils in relation to parent materials is critical in understanding the contribution of parent materials to nickel bioavailability and mobilization within the ecosystem. Sixty soil samples were collected from 0 to 20, 20 to 40 and 40 to 60 cm depths of five pedons dug in each of the parent material locations (Coastal plain sands (CPS), alluvium (ALV), false-bedded sandstones (FBS) and Imo clay shale (ICS)). Distribution of Ni fractions (water soluble (WS), exchangeable (EX), specifically sorbed/carbonate bound (SSC), Iron – Manganese oxides bound (Fe – Mn), organic matter bound (OMB) and residual bound (RE) fractions) was calculated using the modified sequential extraction procedure. The mobility factor (MF) was ascertained using the metal index of mobility (IM) equation. Findings indicated that nickel fractions differed significantly (p < 0.05) with parent materials and soil depths. The SSC Ni prevailed in the soils (40.4–60.4% of total Ni), being higher in ICS soil (4.06–4.34 mg kg−1) and lower in ALV soil (3.89–4.14 mg kg−1). Organic matter bound Ni was the least Ni fraction (0–4.6% of total Ni). High Ni MF was observed (66.5–89.1%).

Strength-increase mechanism and microstructural characteristics of a biotreated geomaterial

Microbially induced calcite precipitation (MICP) is a recently proposed method that is environmentally friendly and has considerable potential applications in artificial biotreated geomaterials. New artificial biotreated geomaterials are produced based on the MICP technology for different parent soils. The purpose of this study is to explore the strength-increase mechanism and microstructural characteristics of the biotreated geomaterial through a series of experiments. The results show that longer mineralization time results in higher-strength biotreated geomaterial. The strength growth rate rapidly increases in the beginning and remains stable afterwards. The calcium ion content significantly increases with the extended mineralization time. When standard sand was used as a parent soil, the calcium ion content increased to a factor of 39 after 7 days. The bacterial cells with attached calcium ions serve as the nucleus of crystallization and fill the pore space. When fine sand was used as a parent soil, the calcium ion content increased to only a factor of 7 after 7 days of mineralization. The nucleus of crystallization could not normally grow because of the limited pore space. The porosity and variation in porosity are clearly affected by the parent soil. Therefore, the strength of the biotreated geomaterial is affected by the parent soil properties, mineralization time, and granular material pore space. This paper provides a basis for theory and experiments for biotreated geomaterials in future engineering practice.

NATURAL AND TECHNOGENIC RADIONUCLIDES IN SOILS IN A SMALL RUSSIAN ARCTIC TOWN

The Onega District is among the first ten municipalities of the Arkhangelsk Region with the highest incidence of neoplasms warranting radiological studies. The aim of this research was to study content and distribution of natural and technogenic radionuclides in the urban soils of the Onega municipality and to identify the main low-intensity radioactive anomalies as well as to provide an objective assessment of radiation risks to health of the local population. Methods: A total of 99 soil samples were taken in several parts of the town. Specific activity of radionuclides was assessed using a gamma spectrometer. Standard soil-morphological, soil-geochemical, radiometric, mathematical-statistical and cartographic methods were applied. Results. Color contrast of the soils in different areas indicates the preservation of their relationship with the parent soil. The values of the effective specific activity of natural radionuclides in soil samples ranged from 28 to 99 Bq/kg. Low-intensity radioactive anomalies were revealed for the first time in town. It was determined that the composition of the town's soils ensures that the effective specific activity of natural radionuclides is not exceeded for materials of classes I and II used in construction. Conclusions. The revealed low-intensity radioactive anomalies can be associated with the influx of radionuclides into the soil as a part of coal combustion products in the local heating stations taking into account the active use of coal combustion products by the local population. It is necessary to assess the long-term effect of low-intensity radioactive anomalies on the population. Further research should concentrate on associations between the epidemiological patterns of diseases and radioactivity in Onega.

A Laboratory Dust Generator Applying Vibration to Soil Sample: Mineralogical Study and Compositional Analyses

AbstractA laboratory study was carried out using a vibrating system (SyGAVib) to produce aerosols from four soils collected in the central Tunisian region around Sfax. The aim of this device is to mimic dust emission by natural wind erosion. Using compositional analysis, the dust produced was compared to (i) dust generated in a wind tunnel by the same soils, (ii) fine sieved and (iii) original bulk soils, and (iv) naturally occurring aerosol samples collected in the same area. The relative quartz content strongly decreases from bulk to fine soils, and again from fine soils to both wind tunnel and vibration‐generated aerosols. Compositional data analysis (CoDA) clearly shows (i) a silica dilution effect in bulk soils, and (ii) that if silica is removed from the composition, the elemental compositions of fine soils and generated aerosols are similar but differ from bulk soils. Both aerosol generation methods produce material with chemical compositions that are also close to those measured in field‐sampled aerosols, and the fine soil composition is much closer to that of field and laboratory aerosols than to the parent soil. Aerosols generated from soils in the laboratory, either using a vibrating system or a wind tunnel, can be used as surrogates of the particles collected directly in the field.

Effect of gypsum content on unsaturated engineering properties of clayey soil

Many of gypsum soils have existed in arid and semi-arid lands. It is considered one of the most problematic soils because of its complicated and unpredicted behavior when exposure to moisture. Extensive researches have been conducted in Iraq to observe the behavior of such soil and to suggest safety restrictions for the collapse and set practical precautions for the structures. This study investigated the effect of gypsum content on some unsaturated engineering properties of a clayey soil. Three different proportions of gypsum (0%, 5% and 20% by weight of the parent soil) were added and tested. The samples have been subjected to swelling potential test, soil water retention curve (SWRC), vapour diffusion and shear strength parameters. It is observed that gypsum content has a significant influence on SWRC, whereas, soil that has high gypsum content made SWRC with higher variables represented by air entry values and residual state. On the other hand, an increase in gypsum content led to a reduction of swelling potential and shear strength parameters. The results of vapour diffusion indicate that gypsum content could modify the microstructure in an unsaturated state and reduce the vapour diffusion through the soil. Â

Soil Carbon Sequestrations in Forest Soils in Relation to Parent Material and Soil Depth in South-Eastern Nigeria

There has been increased interest in soil organic carbon in recent times because of its role in carbon sequestration. Different parent materials affect soil properties and hence will influence how much carbon is sequestered by soil. The study was conducted in June 2019 to investigate soil carbon stock in forest soils with respect to their parent materials in three States in South-eastern Nigeria. Sampling was aided by the location map of the area and free soil survey method was used to locate sampling points. 0ne profile was dug in each location and described using the Food and Agricultural Organization guideline. A total of twelve soil samples were collected and analyzed for selected properties. Results showed that sand content was significantly higher in soils under coastal plain sands (851.96 g·kg−1) and was lowest in soils of Imo clay shale (605.60 g·kg−1). Clay content was higher in soils of Imo clay shale (277.34 g·kg−1) and was lowest in coastal plain sand (118.80 g·kg−1). Silt and clay had moderate variation in coastal plain sand (>15 ≤ 35%) and high variations in Asu River and Imo clay shale (CV > 35%). The soils studied were generally acidic with values ranging (3.52) in soils formed from coastal plain sand, followed by forest soils of Imo clay shale (3.64) and Asu river group (3.85). Soil organic carbon decreased with increase in soil depth in all soil parent materials studied. Mean values ranged from 6.14 g·kg−1 in soil underlain by coastal plain sand to 10.62 g·kg−1) in soils of Imo clay shale. Soil carbon sequestered under the three different parent materials ranged from 1575 - 4676.41 (g·cm−2). Also, soil depth had a notable impact on carbon sequestration with values ranging from 1529.42 - 4374.0541 (g·cm−2) and the thicker the horizon, the more carbon sequestered. Hence, the study concluded that more carbon is sequestered in the subsurface horizons of the soil pedons than in the epipedons.

Complex refractive indices and single-scattering albedo of global dust aerosols in the shortwave spectrum and relationship to size and iron content

Abstract. The optical properties of airborne mineral dust depend on its mineralogy, size distribution, and shape, and they might vary between different source regions. To date, large differences in refractive index values found in the literature have not been fully explained. In this paper we present a new dataset of complex refractive indices (m=n-ik) and single-scattering albedos (SSAs) for 19 mineral dust aerosols over the 370–950 nm range in dry conditions. Dust aerosols were generated from natural parent soils from eight source regions (northern Africa, Sahel, Middle East, eastern Asia, North and South America, southern Africa, and Australia). They were selected to represent the global-scale variability of the dust mineralogy. Dust was resuspended into a 4.2 m3 smog chamber where its spectral shortwave scattering (βsca) and absorption (βabs) coefficients, number size distribution, and bulk composition were measured. The complex refractive index was estimated by Mie calculations combining optical and size data, while the spectral SSA was directly retrieved from βsca and βabs measurements. Dust is assumed to be spherical in the whole data treatment, which introduces a potential source of uncertainty. Our results show that the imaginary part of the refractive index (k) and the SSA vary widely from sample to sample, with values for k in the range 0.0011 to 0.0088 at 370 nm, 0.0006 to 0.0048 at 520 nm, and 0.0003 to 0.0021 at 950 nm, as well as values for SSA in the range 0.70 to 0.96 at 370 nm, 0.85 to 0.98 at 520 nm, and 0.95 to 0.99 at 950 nm. In contrast, the real part of the refractive index (n) is mostly source (and wavelength) independent, with an average value between 1.48 and 1.55. The sample-to-sample variability in our dataset of k and SSA is mostly related to differences in the dust iron content. In particular, a wavelength-dependent linear relationship is found between the magnitude of k and SSA and the mass concentrations of both iron oxide and total elemental iron, with iron oxide better correlated than total elemental iron with both k and SSA. The value of k was found to be independent of size. When the iron oxide content exceeds 3 %, the SSA linearly decreases with an increasing fraction of coarse particles at short wavelengths (&lt; 600 nm). Compared to the literature, our values for the real part of the refractive index and SSA are in line with past results, while we found lower values of k compared to most of the literature values currently used in climate models. We recommend that source-dependent values of the SW spectral refractive index and SSA be used in models and remote sensing retrievals instead of generic values. In particular, the close relationships found between k or SSA and the iron content in dust enable the establishment of predictive rules for spectrally resolved SW absorption based on particle composition.

Plant-Soil Feedbacks of Plantago lanceolata in the Field Depend on Plant Origin and Herbivory

Soil biota involved in plant-soil feedbacks (PSFs) have an impact on the growth of plant individuals. So far, studies investigating the role of soil-biota mediated PSFs in plant performance were mostly performed in greenhouses and focused predominantly on species differences, whereas the contribution of PSFs to plant performance under field conditions and intraspecific variation in PSFs among plant populations remain poorly investigated. Here, we performed a PSF pot experiment under field conditions to study intraspecific variation in plant responses to soil biota. We used seeds from multiple seed families of Plantago lanceolata L. together with Plantago-conditioned soils from contrasting habitats (three non-fertilized pastures vs. three fertilized mown pastures) to test whether plants show a positive or negative response to their parental soil biota. We furthermore tested whether these PSFs depend on microclimate and insect herbivory. To this end, we reciprocally transplanted plants and their soil biota between the two habitat types and excluded aboveground herbivores from half of the plants, respectively. When grown without herbivores, plants from both habitat types showed similar and neutral PSFs independently of the transplant site. In contrast, in the presence of herbivores, PSFs for plants from non-fertilized pastures were negative in both habitats (i.e. plants performed better when they grew with foreign soil biota), whereas PSFs for plants from fertilized mown-pastures remained neutral. Our results suggest that soil biota alone might only play a minor role for performance of P. lanceolata and that the outcome of soil-biota mediated PSFs is modulated by effects of herbivores in different habitats.

The main factors controlling spatial variability of soil organic carbon in a small karst watershed, Guizhou Province, China

Soil organic carbon (SOC) is an important component of the global carbon pool. Assessment of SOC in a karst mountainous area is a great challenge due to the high spatial heterogeneity in topography, land use and soil. This study used 2755 soil samples from a karst watershed in southwestern China to quantitatively study the spatial variability in SOC in this small karst watershed. The effects of parent soil material, soil type, land use, slope position, slope orientation and rock exposure rate on the spatial distributions of SOC in the karst watershed were compared by statistical modelling. The results showed that the SOC content in the study area was 25.01 g/kg, and the coefficient of variation was 55.26%, indicating moderate-intensity variation. The nugget coefficient C0/(C0 + C) was >0.70, and the spatial distribution of SOC was mainly affected by structural factors. Parent soil material, soil type, land use, slope position, slope direction and rock exposure rate had significant effects on the SOC (p < 0.001). The independent interpretation of SOC spatial variation by influencing factors is as follows: soil family level (37.40%) > land use (23.10%) > rock exposure rate (22.10%) > soil group level (17.50%) > parent material (10.90%) > slope position (7.20%) > slope direction (5.10%). Soils in the lower soil categories of the soil classification system were better able to reflect SOC spatial distributions. When soil family levels, land uses and rock exposure rates are used as predictors, 56.60% of SOC variability can be explained. Therefore, it is advisable to use a combination of soil family levels, land uses and rock exposure rates as the main controlling factor for predicting or assessing SOC spatial distributions in karst areas.

Microbial community responses reduce soil carbon loss in Tibetan alpine grasslands under short-term warming.

Changes in labile carbon (LC) pools and microbial communities are the primary factors controlling soil heterotrophic respiration (Rh ) in warming experiments. Warming is expected to initially increase Rh but studies show this increase may not be continuous or sustained. Specifically, LC and soil microbiome have been shown to contribute to the effect of extended warming on Rh . However, their relative contribution is unclear and this gap in knowledge causes considerable uncertainty in the prediction of carbon cycle feedbacks to climate change. In this study, we used a two-step incubation approach to reveal the relative contribution of LC limitation and soil microbial community responses in attenuating the effect that extended warming has on Rh . Soil samples from three Tibetan ecosystems-an alpine meadow (AM), alpine steppe (AS), and desert steppe (DS)-were exposed to a temperature gradient of 5-25°C. After an initial incubation period, soils were processed in one of two methods: (a) soils were sterilized then inoculated with parent soil microbes to assess the LC limitation effects, while controlling for microbial community responses; or (b) soil microbes from the incubations were used to inoculate sterilized parent soils to assess the microbial community effects, while controlling for LC limitation. We found both LC limitation and microbial community responses led to significant declines in Rh by 37% and 30%, respectively, but their relative contributions were ecosystem specific. LC limitation alone caused a greater Rh decrease for DS soils than AMs or ASs. Our study demonstrates that soil carbon loss due to Rh in Tibetan alpine soils-especially in copiotrophic soils-will be weakened by microbial community responses under short-term warming.

Sampling Size Requirements to Delineate Spatial Variability of Soil Properties for Site-Specific Nutrient Management in Rubber Tree Plantations

Site-specific nutrient management is an important strategy to promote sustainable production of rubber trees in order to obtain high yields of natural rubber. Making effective nutrient management decisions for rubber trees depend on knowing the spatial variations of soil fertility properties in advance. In this study the Kriging geostatistical method was used to examine the spatial variability of soil total nitrogen (TN), organic matter (OM), available phosphorus (AP) and available potassium (AK) in a typical hilly rubber tree plantation in Hainan, China. The spatial variability of the soils was small for the TN and OM and had medium variability for the AP and AK variables. Anisotropic semivariograms of all soil properties revealed that elevation and building contour ledge can profoundly affect the spatial variability of soil properties in the plantation, except for the AK variable. Soil samples had to be collected in alignment with the direction of elevation and perpendicular to the direction of building contour ledges, which was needed to obtain more reliable information within the study area in the rubber tree plantation. In formulating a sample scheme for AK, the distribution features of the soil's parent material should be considered as the influence factor in the study field. The Kriging method used to guide the soil sampling for spatial variability dertermination of soil properties was about 2-5 times more efficient than the classic statistical method.