Possibilities of using the Landau–Deryagin law to evaluate soil degradation as a result of its contamination with chlorides

The contamination of heavy loamy chernozem by iron, sodium, magnesium, calcium, and hydrogen chlorides (2% of soil mass) decreases soil moisture content (W, percent of soil mass) in the interval of the soil moisture pressure (Р) from 0.0 to–0.6 atm, which indicate soil degradation. In a range of P from–0.2 to–0.6 atm, there is a close correlation between the logarithm of Р module (log|P|) and W and, therefore, a regression relationship log|P _W | = |P ₀|–kW, where |P ₀| and k are empirically determined parameters. This relationship is similar to the Landau–Deryagin law. The parameters |P ₀| and k are also in a close correlation, which is described by the regression equation |P ₀| = 29.3k–0.557. At chernozem contamination by chlorides, the |P ₀| and k parameters become smaller, and so they may be used for the evaluation of degradation of chloride-contaminated soils.     

Effect of surface heterogeneity on phosphorus adsorption onto mineral particles: experiments and modeling

Purpose

Adsorptive interaction at the solid-water interface plays an important role in the fate and behavior of phosphorus (P) in rivers and lakes and the resulting eutrophication. This study aims to investigate the contributions of heterogeneous morphology to P adsorption onto mineral particles.

Materials and methods

The dominant minerals in Yellow River sediment, quartz, k-feldspar, and calcite are investigated with adsorption experiments and microscopic examinations. Taylor expansion is applied to quantitatively characterize the heterogeneous surface morphology.

Results and discussion

The results reveal that locally concave or convex micro-morphology characterized by the second derivative term of the Taylor expansion, F ₂, can be related to adsorption capacity due to its effect on surface-charge density and distribution. The distribution of adsorbed P as a function of F ₂ was determined for selected particles composed of each of the pure minerals and was fit to a Weibull distribution. Each mineral was characterized by F _2a , the weighted average value of F ₂, and Weibull distribution factors, and correlated with sorption isotherms. The developed relationships were used to accurately predict adsorption onto individual particles as well as pure mineral samples.

Conclusions

Mineral particles have complex surface morphology, which affects the interface P adsorption. Micro-morphological characterization of F ₂ and F _2a can be used to predict adsorption onto the pure minerals, and this study provides physical basis for predicting adsorption on sediment particles composed of these minerals.

     

Effect of Metals on Decolorization of Reactive Blue HERD by <Emphasis Type="Italic">Comamonas</Emphasis> sp. UVS

Comamonas sp. UVS was able to decolorize Reactive Blue HERD (RBHERD) dye (50 mg L^?1) within 6 h under static condition. The maximum dye concentration degraded was 1,200 mg L^?1 within 210 h. A numerical simulation with the model gives an optimal value of 35.71?±?0.696 mg dye g^?1 cell h^?1 for maximum rate (V_max) and 112.35?±?0.34 mg L^?1 for the Michaelis constant (K_m). Comamonas sp. UVS has capability of decolorization of RBHERD in the presence of Mg²⁺, Ca²⁺, Cd²⁺, and Zn²⁺, whereas decolorization was completely inhibited by Cu²⁺. Metal ions also affected the levels of biotransformation enzymes during decolorization of RBHERD. Comamonas sp. UVS was also able to decolorize textile effluent with significant reduction in COD. The biodegradation of RBHERD dye was monitored by UV–vis spectroscopy, FTIR spectroscopy, and HPLC.     

Abundance of transcripts of functional gene reflects the inverse relationship between CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O emissions during mid-season drainage in acidic paddy soil

Agricultural management significantly affects methane (CH₄) and nitrous oxide (N₂O) emissions from paddy fields. However, little is known about the underlying microbiological mechanism. Field experiment was conducted to investigate the effect of the water regime and straw incorporation on CH₄ and N₂O emissions and soil properties. Quantitative PCR was applied to measure the abundance of soil methanogens, methane-oxidising bacteria, nitrifiers, and denitrifiers according to DNA and mRNA expression levels of microbial genes, including mcrA, pmoA, amoA, and nirK/nirS/nosZ. Field trials showed that the CH₄ and N₂O flux rates were negatively correlated with each other, and N₂O emissions were far lower than CH₄ emissions. Drainage and straw incorporation affected functional gene abundance through altered soil environment. The present (DNA-level) gene abundances of amoA, nosZ, and mcrA were higher with straw incorporation than those without straw incorporation, and they were positively correlated with high concentrations of soil exchangeable NH₄⁺ and dissolved organic carbon. The active (mRNA-level) gene abundance of mcrA was lower in the drainage treatment than in continuous flooding, which was negatively correlated with soil redox potential (Eh). The CH₄ flux rate was significantly and positively correlated with active mcrA abundance but negatively correlated with Eh. The N₂O flux rate was significantly and positively correlated with present and active nirS abundance and positively correlated with soil Eh. Thus, we demonstrated that active gene abundance, such as of mcrA for CH₄ and nirS for N₂O, reflects the contradictory relationship between CH₄ and N₂O emissions regulated by soil Eh in acidic paddy soils.     

Quantitative indices of the distribution of substances in the soil-plant system

New methodological approaches and an algorithm for the quantitative assessment of accumulating a substance by a plant (C _p ) with due regard for its concentration in the soil (C _n ) are proposed. The first approach is the approximation of concentration curves by the functions C _p = f(C _n ) and their parameters. The second one is the standardization of the coefficients of biological sorption (K _b ) of a substance upon its stable concentration in the soil using the function K _b = f(C _n ). As compared to the variation-statistical values of the mean and extreme concentrations, or the coefficients K _b , the proposed parameters are characterized by a higher accuracy and sensitivity. They may be successfully used for quantitative studies of the mechanism and the intensity of the absorption of substances by plants, for the prediction of the accumulation of substances in the trophic chain, and the assessment of soil self-purification (detoxification) and comparative ratings.     

Predicting soil loss in central and south Italy with a single USLE-MM model

Purpose

The USLE-MM estimates event normalized plot soil loss, A_e,N, by an erosivity term given by the runoff coefficient, Q_R, times the single-storm erosion index, EI₃₀, raised to an exponent b₁?>?1. This modeling scheme is based on an expected power relationship, with an exponent greater than one, between event sediment concentration, C_e, and the EI₃₀/P_e (P_e = rainfall depth) term. In this investigation, carried out at the three experimental sites of Bagnara, Masse, and Sparacia, in Italy; the soundness of the USLE-MM scheme was tested.

Materials and methods

A total of 1192 (A_e,N, Q_REI₃₀) data pairs were used to parameterize the model both locally and considering all sites simultaneously. The performances of the fitted models were established by considering all erosive events and also by distinguishing between events of different severity.

Results and discussion

The b₁ exponent varied widely among the three sites (1.05–1.44) but using a common exponent (1.18) for these sites was possible. The A_e,N prediction accuracy increased in the passage from the smallest erosion events (A_e,N?≤?1 Mg ha^?1, median error =?3.35) to the largest ones (A_e,N?>?10 Mg ha^?1, median error =?1.72). The Q_REI₃₀ term was found to be usable to predict both A_e,N and the expected maximum uncertainty of this prediction. Soil erodibility was found to be mainly controlled by the largest erosion events.

Conclusions

Development of a single USLE-MM model appears possible. Sampling other sites is advisable to develop a single USLE-MM model for a general use.

     

Temporal variations of soil respiration at multiple timescales in a spruce-fir valley forest,northeastern China

Purpose

There is a paucity of data regarding the multiple timescale variations of heterotrophic respiration (R _H) and autotrophic respiration (R _A) as well as the primary controlling factors. The objective of this study is to find the temporal variations of total soil respiration (R _S) and its components, revealing the driving factors at different timescales.

Materials and methods

A trenching method was used to distinguish R _S, R _H, and R _A in a spruce-fir valley forest in northeastern China. We used the closed dynamic chamber method to measure the soil respiration rate. Analyses of R _S, R _H, and R _A in relation to biotic and abiotic factors were conducted to realize the temporal variations at different timescales.

Results and discussion

Only R _S and R _H showed a distinct diurnal variation and soil temperature (T _S) can explain 68 and 59 % of the daily variation, respectively. R _S, R _H, and R _A showed a pronounced, single peak curve seasonally, and T _S can explain 11–95 % of the seasonal variation. Soil moisture (W _S) maintained at a relatively high level and was not related to R _S, R _H, or R _A on a seasonal scale, and there was no significant relationship between the seasonal R _S, R _A, and root biomass. However, for 5 years, only the mean R _A of the growing season was significantly related to the mean W _S, which can explain 39 % of the inter-annual variation of R _A. The annual variations of litterfall and the relative growth rate of stems were not related to R _S, R _H, or R _A. The contribution of R _H to R _S was larger, and the temperature sensitivity was 2.01–3.71 for R _S, 1.90–3.08 for R _H, and 2.20–5.65 for R _A.

Conclusions

R _S, R _H, and R _A show different temporal variations at multiple timescales. When W _S is not restricted, T _S is the primary driving factor of daily and seasonal variation of R _S and R _H. In this site, R _H accounts for a large proportion of R _S and plays a crucial role in determining the magnitude and temporal variation of R _S.

     

Oxygen Transfer Numerical Investigation Using Intermittent Aeration Technology Under Regular Waves

Based on a combination of Reynolds-Averaged Navier-Stokes equations, standard k-ε equations, and VOF technique, a 2-D dissolved oxygen transport mathematical model was conducted to investigate oxygen-supply characteristics for regular waves with a given still water depth d and various hydrodynamic parameters (incident wave height H and wave period T equivalent to incident wave length L) and intermittent aeration parameters (air flow rate per unit width q, aeration period T_a, aeration depth d_a and air source area A_a). A series of experiments were conducted to validate the mathematical model, and they agreed well with each other. In addition, a series of dimensionless parameters were conducted to assess their relationships with oxygen transfer coefficient respectively. It was found that oxygen transfer coefficient increased slightly with the increase of \( q/{g}^2{T}_a^3 \). With the increasing \( {d}_a^2/{A}_a \), oxygen transfer coefficient increased obviously for the small \( {d}_a^2/{A}_a \) scenarios; however, it increased slightly for the high \( {d}_a^2/{A}_a \) scenarios. With increasing HL/d², a linear increase tendency of oxygen transfer coefficient appeared approximately. Furthermore, a simple prediction formula for oxygen transport coefficient was conducted using the numerical data, the dimensional analysis, and the least squares method, and it was validated well with the related experimental data.     

Contribution of Soil Components on the Sorption of Chlorpyrifos

It is generally assumed that the sorption of a nonionic pesticide on soil depends mainly on the content of soil organic matter (SOM); however, there are other factors that can contribute to this process. The possible causes of variation in the carbon-normalized partition coefficient (K _OC) for chlorpyrifos (CPF) for a diverse set of ten soils have been investigated. On the one hand, the analysis of the chemical composition of the SOM was analyzed, and on the other hand, the likely interactions between the organic matter and the mineral phase were assessed. Sorption experiments of CPF were performed on whole soil, on soils treated with 2% hydrofluoric acid (HF), and onto calcined soil at 550 °C. Organic matter chemistry of soil was determined by ¹³C CP/MAS NMR spectroscopy; K _OC values were positively correlated with aryl C relative proportion and negatively correlated with alkyl C and O-aryl C proportions and prediction equation of K _OC was found (R ²?=?0.82, p?<?0.001). To evaluate possible organo-mineral interactions, a mathematical model was proposed which calculates the concentration of CPF at equilibrium (C _cal) considering adsorption coefficients for the organic (K _DHF) and inorganic (K _D550 °C) soil constituents, separately. The comparison between C _cal and the equilibrium concentration obtained from experimental data (C _exp) onto whole soil allowed us to confirm that interactions between the OM and clay affect the adsorption of CPF in whole soil. Such findings should be taken into account in the development of predictive models for the evaluation of the fate and transport of this pesticide in soil.     

A Mechanistic Model for Secchi Disk Depth,Driven by Light Scattering Constituents

An optics theory-based mechanistic model for Secchi disk depth (Z _SD) is advanced, tested, and applied for Cayuga Lake, NY. Robust data sets supported the initiative, including for (1) Z _SD, (2) multiple light attenuation metrics, most importantly the beam attenuation (c) and particulate scattering (b _p) coefficients, and (3) measures of constituents responsible for contributions to b _p by phytoplankton (b _o) and minerogenic particles (b _m). The model features two serially connected links. The first link supports predictions of b _p from those for b _o and b _m. The second link provides predictions of Z _SD based on those for b _p, utilizing an earlier optical theory radiative transfer equation. Recent advancements in mechanistically strong estimates of b _m, empirical estimates of b _o, and more widely available bulk measurements of c and b _p have enabled a transformation from a theory-based conceptual to this implementable Z _SD model for lacustrine waters. The successfully tested model was applied to quantify the contributions of phytoplankton biomass, and minerogenic particle groups, such as terrigenous clay minerals and autochthonously produced calcite, to recent b _p and Z _SD levels and dynamics. Moreover, it has utility for integration as a submodel into larger water quality models to upgrade their predictive capabilities for Z _SD.     

Estimation of natural outcrossing rate and genetic diversity in Lima bean (<Emphasis Type="Italic">Phaseolus lunatus</Emphasis> L. var. <Emphasis Type="Italic">lunatus</Emphasis>) from Brazil using SSR markers: implications for conservation and breeding

Lima bean (Phaseolus lunatus L.) is an important food source in Brazil, especially in the northeast region, where its production and consumption are high. The goals of the present study were to estimate natural outcrossing rates and genetic diversity levels of Lima bean from Brazil, using ten microsatellite loci to obtain information for their conservation and breeding. Fourteen accessions were selected from an experiment in field with open-pollinated and with the presence of pollinating insects. Twelve seeds of each of the 14 selected accessions were grown in screenhouse for tissue harvest and DNA extraction. The multilocus model was used to determine the reproductive system. The outcrossing rate was 38.1 % (t_m = 0.381; t_s = 0.078), and the results indicated a mixed mating system with a predominance of selfing (1 ? t_m = 61.9 %). The biparental inbreeding rate was high (t _m  ? t _s  = 0.303) and the multilocus correlated paternity was quite high (r _p(m) = 0.889), indicating that the progeny was mostly composed of full sibs. The average effective number of pollen donors per maternal plant (N _ep ) was low (1.12), and the fixation index for maternal genotypes (F _m ) was 0.945, indicating that most genitors resulted from inbreeding. The studied families presented considerable genetic variability: A = 6.10;  %P = 30; H _e  = 0.60 and H _o  = 0.077. Total diversity was high (H _T = 0.596), and a portion was distributed within families (H _S = 0.058). In addition, diversity was higher between families (D _ST = 0.538), and genetic differentiation was high (G _ST = 0.902). The results presented here can be used in the implementation of Lima bean conservation and breeding programs in Brazil.     

Adsorption of 2,4,6-Trichlorophenol and <Emphasis Type="Italic">ortho</Emphasis>-Nitrophenol from Aqueous Media Using Surfactant-Modified Clinoptilolite–Polypropylene Hollow Fibre Composites

Natural clinoptilolite was modified with hexadecyltrimethylammonium chloride, a cationic surfactant, and then melt-mixed with polypropylene hollow fibres to produce polymer composites with adsorptive properties. The performance of the fabricated composites was evaluated by optimizing experimental parameters such as surfactant loading, contact time, pH and initial concentration for the adsorptive removal of 2,4,6-trichlorophenol (TCP) and ortho-nitrophenol (o-NP). Based on the fourier transmission infrared spectra and scanning electron microscopy micrographs of as-received and surfactant-modified clinoptilolite, the modification of natural clinoptilolite was attained. The composites showed enhanced adsorption capability for TCP over o-NP with removal efficiencies of 84% and 46%. Loading the clinoptilolite with surfactant concentrations beyond 8 mM reduced the adsorption capacity. The removal of TCP and o-NP was found to depend critically on the pH of the solution, and the optimum ranges were 4–6 and 2–6 for compounds, respectively. The adsorption dynamics were determined with first- and second-order kinetics models, and the adsorption system for TCP and o-NP followed the first-order kinetics. Adsorption isotherm analysis revealed that the adsorption equilibrium data obeyed/fit the Freundlich isotherm.     

Estimation of soil saturated hydraulic conductivity by artificial neural networks ensemble in smectitic soils

The saturated hydraulic conductivity (K_s) of the soil is one of the main soil physical properties. Indirect estimation of this parameter using pedo-transfer functions (PTFs) has received considerable attention. The Purpose of this study was to improve the estimation of K_s using fractal parameters of particle and micro-aggregate size distributions in smectitic soils. In this study 260 disturbed and undisturbed soil samples were collected from Guilan province, the north of Iran. The fractal model of Bird and Perrier was used to compute the fractal parameters of particle and micro-aggregate size distributions. The PTFs were developed by artificial neural networks (ANNs) ensemble to estimate K_s by using available soil data and fractal parameters. There were found significant correlations between K_s and fractal parameters of particles and microaggregates. Estimation of K_s was improved significantly by using fractal parameters of soil micro-aggregates as predictors. But using geometric mean and geometric standard deviation of particles diameter did not improve K_s estimations significantly. Using fractal parameters of particles and micro-aggregates simultaneously, had the most effect in the estimation of K_s. Generally, fractal parameters can be successfully used as input parameters to improve the estimation of K_s in the PTFs in smectitic soils. As a result, ANNs ensemble successfully correlated the fractal parameters of particles and micro-aggregates to K_s.     

Molecular cytogenetic identification of newly synthetic <Emphasis Type="Italic">Triticum kiharae</Emphasis> with high resistance to stripe rust

Six new amphiploids, Triticum kiharae Dorof. et Migusch. (2n?=?6x?=?42, A^tA^tGGDD), are described in this study. They were developed by the chromosome doubling of F₁ hybrid crosses between Triticum timopheevii Zhuk. (A^tA^tGG) with high resistance to stripe rust and Aegilops tauschii Cosson (DD) by colchicine treatment. These amphiploids showed a high level of fertility of 68–80% and exhibited relatively normal chromosome pairing in meiotic metaphase I. Individual chromosomes of T. kiharae could be identified by multicolor fluorescence in situ hybridization using the combination of oligonucleotides probes Oligo-pSc119.2-1, Oligo-pTa535-1, and Oligo-pTa71-2. T. kiharae exhibited high resistance to predominant stripe rust races CYR34, CYR31, CYR32, CYR33, and SY11-4 both during the seedling and adult stages. However, high molecular weight glutenin subunits from Ae. tauschii parents were only partially expressed in the T. kiharae background. These T. kiharae lines provide novel materials to widen the genetic diversity of the common wheat gene pool.     

Root Porosity Changes in <Emphasis Type="Italic">Salix nigra</Emphasis> Cuttings in Response to Copper and Ultraviolet-B Radiation Exposure

Cuttings of black willow (Salix nigra), a naturally occurring wetland species, are used for restoration and streambank stabilization. As an adaptation to their wetland habitat, this species develops aerenchyma tissue to avoid root anoxia. To determine the effects of combined copper and ultraviolet-B radiation exposure on aerenchyma tissue (measured as root porosity), black willow cuttings were grown hydroponically and exposed to three ultraviolet-B (UV-B) intensities and three Cu concentrations in a completely randomized 3?×?3 factorial design. While both UV-B (F _2,42?=?11.45; p?=?0.0001) and Cu (F _2,42?=?6.14; p?=?0.0046) exposure increased root porosity, total biomass decreased in response to both UV-B (F _2,43?=?3.36; p?=?0.0441) and to Cu (F _2,43?=?4.03; p?=?0.0249). Root biomass decreased only in response to Cu (F _2,41?=?3.41; p?=?0.0427) resulting in a decrease in the root/shoot ratio (F _2,42?=?3.5; p?=?0.0393). Copper exposure also resulted in a decrease in the number of leaves/shoot (F _2,42?=?7.03; P?=?0.0023). No UV-B and Cu interaction was found. While the present research indicates the negative effects of Cu contamination and elevated UV-B intensities on S. nigra, it also points out potential mechanisms that S. nigra uses to alleviate these stresses.     

Genetic diversity and relationships of wild and cultivated <Emphasis Type="Italic">Zanthoxylum</Emphasis> germplasms based on sequence-related amplified polymorphism (SRAP) markers

The genus Zanthoxylum, belonging to Rutaceae, has a long history of cultivation both for economic and chemical values in China. To effectively conserve and sustainably utilize this genus resource, a study on genetic diversity and relationships of Zanthoxylum germplasms was carried out by employing SRAP markers. We used 16 primer combinations to assess genetic variations and relationships among 175 accessions from eight cultivated provenances, including Shandong, Henan, Shanxi, Shaanxi, Gansu, Sichuan, Guizhou and Yunnan. A total of 145 clear repetitive and intense bands were yielded, and the percentage of polymorphic bands was 100 % for per primer combination, indicating a relatively high diversity among Zanthoxylum germplasms. From a geographic perspective, the highest genetic diversity level was observed within Guizhou provenance (N _a  = 1.97, Ne = 1.52, H = 0.31, I = 0.46) while Henan provenance had the lowest genetic diversity (N _a  = 1.68, Ne = 1.45, H = 0.25, I = 0.37). Based on AMOVA results, the abundant genetic variation was mainly caused by variation of intra-provenances (84.96 %), rather than among provenances (15.038 %). The results indicated low genetic differentiation (G _st  = 0.133) and high gene flow (N _m  = 3.2605) among provenances. The neighbor-joining tree revealed that the 175 accessions could be divided into four groups, and groupings indicated a divergence between the cultivated accessions of Zanthoxylum bungeanum Maxim. and Z. armatum DC. Moreover, three accessions of Z. piperitum DC. var. inerme without prickles introduced from Japan gathered one cluster. Cluster IV is composed of accessions of different geographical origin, including 11 wild species and 10 cultivated accessions of Z. bungeanum. The cluster analysis also reflected a relatively close relationship between the geographical origins and the classification of accessions in cluster I. Structure analysis indicated that collected Zanthoxylum accessions could be divided into two major groups. The information obtained from our research would benefit to make use of Zanthoxylum germplasms and assist the management of a Zanthoxylum germplasms collection.     

Potentialities of Six Plant Species on Phytoremediation Attempts of Fuel Oil-Contaminated Soils

A field experiment investigating the phytoremediation potential of six plant species—Goosegrass (Eleusine indica), Bermuda grass (Cynodon dactylon), Sessile joyweed (Alternanthera sessilis), Benghal dayflower (Commelina benghalensis), Lovanga (Cleome ciliata), and Chinese violet (Asystasia gangetica)—on soil contaminated with fuel oil (82.5 ml/kg of soil) have been conducted from March to August 2016. The experiments consider three modalities—Tn: unpolluted planted soils, To: unplanted polluted soils, and Tp: polluted planted soil—randomized arranged. Only three (E. indica, C. dactylon, and A. sessilis) of the six species survived while the others died 1 month after the beginning of experimentations. The relative growth indexes showed a strong similarity between the growth parameters of E. indica and C. dactylon, each on polluted and control soils, unlike A. sessilis. Total petroleum hydrocarbons (TPHs) removal efficiency were 82.56, 80.69, and 77% on soil planted with E. indica, C. dactylon, and A. sessilis, respectively; and 57.25% on non-planted soil. According to the bioconcentration and translocation factors, E. indica and A. sessilis are involved on rhizodegradation and phytoextraction of hydrocarbons whereas C. dactylon is only involved into rhizodegradation. Overall, E. indica and C. dactylon out-yielded A. sessilis in the phytoremediation capacity of fuel oil-contaminated soils.     

Differential influence of four invasive plant species on soil physicochemical properties in a pot experiment

Purpose

This study compared the effects of four invasive plants, namely Impatiens glandulifera, Reynoutria japonica, Rudbeckia laciniata, and Solidago gigantea, as well as two native species—Artemisia vulgaris, Phalaris arundinacea, and their mixture on soil physicochemical properties in a pot experiment.

Materials and methods

Plants were planted in pots in two loamy sand soils. The soils were collected from fallows located outside (fallow soil) and within river valley (valley soil) under native plant communities. Aboveground plant biomass, cover, and soil physicochemical properties such as nutrient concentrations, pH, and water holding capacity (WHC) were measured after two growing seasons. Discriminant analysis (DA) was used to identify soil variables responsible for the discrimination between plant treatments. Identified variables were further compared between treatments using one-way ANOVA followed by Tukey’s HSD test.

Results and discussion

Plant biomass, cover, and soil parameters depended on species and soil type. DA effectively separated soils under different plant species. DA on fallow soil data separated R. laciniata from all other treatments, especially I. glandulifera, native species and bare soil, along axis 1 (related mainly to exchangeable K, N-NH₄, total P, N-NO_3, and WHC). Large differences were found between R. laciniata and S. gigantea as indicated by axis 2 (S-SO₄, exchangeable Mg, total P, exchangeable Ca, and total Mg). DA on valley soil data separated R. japonica from all other treatments, particularly S. gigantea, R. laciniata, and native mixture, along axis 1 (N-NO₃, total N, S-SO₄, total P, pH). Along axis 2 (N-NO₃, N-NH₄, Olsen P, exchangeable K, WHC), large differences were observed between I. glandulifera and all other invaders.

Conclusions

Plant influence on soil differed both among invasive species and between invasive and native species. Impatiens glandulifera had a relatively weak effect and its soil was similar to both native and bare soils. Multidirectional effects of different invaders resulted in a considerable divergence in soil characteristics. Invasion-driven changes in the soil environment may trigger feedbacks that stabilize or accelerate invasion and hinder re-colonization by native vegetation, which has implications for the restoration of invaded habitats.

     

Estimation of the cover and management factor based on stratified coverage and remote sensing indices: a case study in the Loess Plateau of China

Purpose

We attempt to describe the cover and management (C) factor more comprehensively through the use of a simple and efficient method.

Materials and methods

We measure the coverage of each vegetation layer and C factor for 152 sampled plots in the Ansai watershed. We propose four stratified coverage indices (green coverage (V _G), total coverage (V _T), probability coverage (V _P), weight coverage (V _W)), derive green and yellow vegetation indices from Landsat 8 OLI images to reflect green and residue cover, and construct and validate C factor estimation models from stratified coverage and remote sensing indices, respectively.

Results and discussion

(1) V _T and V _P present C factor estimation advantages for grassland and shrub land. V _W can better illustrate the C factor due to the relatively complete spatial structuring of woodland and orchard land. For cropland, four stratified coverage indices present the same estimation capacities for the C factor. Except for cropland and grassland, the estimation capabilities of V _G are relatively low because the residue layer is ignored. (2) The C factor is more sensitive to yellow vegetation indices, which indicates that senescent fractional cover and litter are important and cannot be ignored. The linear and non-linear models can explain 56.6 and 61.8% of C factor variation, respectively, and the linear model is more accurate than the non-linear model. (3) Compared to traditional indices (projective coverage and single remote sensing indices), stratified coverage indices and a combination of several remote sensing indices can estimate the C factor more effectively.

Conclusions

At the field scale, the C value estimation model can be selected according to the land-use type. At the watershed and regional scales, a linear model is recommended for C factor estimation.

     

The Magnetic Susceptibility and Iron Oxides of Aquic Soils in Southern Iran

An investigation of the effect of aquic conditions on Fe-oxides distribution and magnetic susceptibility (χ_lf) was conducted on selected soils from Southern Iran. Seven pairs of adjacent soil pedons with different soil moisture regimes (aquic and non-aquic), were selected. The average concentrations of poorly crystalline Fe (Fe_o) and total free Fe (Fe_d) in aquic soils were 0.2 and 0.07% respectively, and 0.45 and 0.9% in non-aquic soils, respectively. The ratio of Fe_o/Fe_d varied from 0.03 to 0.64. χ_lf ranged from 1.8 to 113 × 10^?8 m³ kg^?1 in the soil studied. The variation of χ_fd ranged from 0.0 to 9.65%. The χ_fd values observed in non-aquic soils were larger than in aquic soils (4.00% vs. 1.37%). Positive correlations were observed between χ and clay contents in both aquic and non-aquic soils; however, non-aquic soil samples showed a larger coefficient of determination. A positive correlation existed between χ_fd and χ in aquic and non-aquic soils. Higher values of χ_fd were observed at the soil surface of non-aquic soil samples than at deeper levels, suggesting a greater proportion of ultrafine grains. Of the soil properties that were assessed, clay, cation exchangeable capacity (CEC), Fe_d, Fe_o/Fe_d ratio, χ_lf and χ_fd contents, changed significantly in response to the aquic condition.