Arsenic-contaminated soils phytotoxicity studies with sunflower and sorghum

Background, Aim and Scope  Environmental pollution caused by arsenic (As) is a major ecological problem. There has been intense worldwide effort to find As-hyperaccumulating plants that can be used in phytoremediation—the green-plant-assisted removal of chemical pollutants from soils. For phytoremediation, it is natural to prefer cultivated rather than wild plants, because their agriculture is well known. This study was conducted to evaluate the tolerance of common sunflower(Helianthus annuus L.) and sugar sorghum(Sorghum saccharatum Pers.) for soil-As contents of 10–100 mg As kg^-1 soil, with sodium arsenite as a model contaminant. Methods  Plants were grown in a growth chamber for 30 days. Microfield experiments were conducted on experimental plots. To study the phytoremediation effect of the auxins indole-3-acetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D), we treated 1- and 3-day-old plant seedlings with water solutions of the auxins (concentrations 10^-5, 10^-7, and 10^-9 g l^-1). The soil and plant-biomass samples were analyzed for total As by using the color reaction of ammonium molybdate with As. Results and Discussion  Phytotoxicity studies showed that 100 mg As kg^-1 soil poisoned sunflower and sorghum growth by 50%. There was a linear correlation between soil-As content and As accumulation in the plants. Laboratory experiments showed that the soil-As content was reduced two- to threefold after sunflower had been grown with 10–100 mg As kg^-1 soil for 30 days. Treatment of sunflower and sorghum seedlings with IAA and 2,4-D at a concentration of 10^-5 g l^-1 in microfield experiments enhanced the phytoremediation two- to fivefold as compared with untreated control plants. The best results were obtained with 3-day-old seedlings. Conclusion, Recommendation and Outlook  (a) Sunflower and sorghum are good candidates to remediate As-polluted soils. (b) Phytoremediation can be improved with IAA or 2,4-D. (c) Mixed cropping of sorghum and sunflower may be another way of improving phytoremediation.     

Contact angles at the water–air interface of hydrocarbon-contaminated soils and clay minerals

Contact angles at the water–air interface have been measured for triturated preparations of clays and soils in order to assess changes in their hydrophobic properties under the effect of oil hydrocarbons. Tasks have been to determine the dynamics of contact angle under soil wetting conditions and to reveal the effect of chemical removal of organic matter from soils on the hydrophilicity of preparations. The potentialities of static and dynamic drop tests for assessing the hydrophilic–hydrophobic properties of soils have been estimated. Clays (kaolinite, gumbrine, and argillite) have been investigated, as well as plow horizons of soils from the Republic of Tatarstan: heavy loamy leached chernozem, medium loamy dark gray forest soil, and light loamy soddy-calcareous soil. The soils have been contaminated with raw oil and kerosene at rates of 0.1–3 wt %. In the uncontaminated and contaminated chernozem, capillary water capacity has been maintained for 250 days. The contact angles have been found to depend on the degree of dispersion of powdered preparation, the main type of clay minerals in the soil, the presence and amount of oxidation-resistant soil organic matter, and the soil–water contact time. Characteristic parameters of mathematical models for drop behavior on triturated preparations have been calculated. Contamination with hydrocarbons has resulted in a reliable increase in the contact angles of soil preparations. The hydrophobization of soil surface in chernozem is more active than in soils poorer in organic matter. The complete restoration of the hydrophilic properties of soils after hydrocarbon contamination is due to the oxidation of easily oxidizable organic matter at the low content of humus, or to wetting during several months in the absence of the mazut fraction.     

Simulation of tridecane degradation under different soil water contents

A mathematical model for the degradation of n-tridecane in a leached chernozem with different water contents was developed on the basis of budget ratios and the Mono kinetic equations. In the course of the verification, the model equations were simplified and solved numerically. The cases of uniform and step-wise initial pollutant distributions in a soil-filled co lumn were considered. The model was refined in accordance with the experimental data on the decrease in the tridecane concentration during three months. A statistically significant positive effect of the moisture and the uncontaminated upper soil layer on the rate of the tridecane decrease was shown. It was found that the degradation of the tridecane stopped and then recommenced again. The tridecane concentration in the soil at which its decrease almost stopped was determined. It was supposed that the hydrocarbon-oxidizing microorganisms, in the course of their life activity, excrete products that are accumulated and inhibit the degradation of the hydrocarbon. The parameters of the microbial activity in the soil were determined in a numerical experiment.     

Reciprocal compatibility within the genus Pisum L. as studied in F1 hybrids: 4. Crosses within P. sativum L. subsp. elatius (Bieb.) Aschers. et Graebn.

Genetic Resources and Crop Evolution - Five accessions representing divergent lineages of wild peas (Pisum sativum subsp. elatius) were crossed with each other in both directions and also...     

Heterogeneity of Wetting Contact Angle in Hydrophobized Soils and Parent Rocks

Eurasian Soil Science - A number of soils and parent rocks at different stages of weathering were investigated for the formation of heterogeneous wettability under residual hydrophobic...     

The first record of tetrasomy in pea (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.)

Tetrasomic plants with two additional small chromosomes were identified, with a frequency about 2.5%, in the trisomic pea line TRUST-R, which normally contains one extra chromosome covering a sporophyte lethal in the regular chromosome set. As compared to trisomics, tetrasomics exhibited an enhanced expression of the traits resulting from extra chromosome addition: slow growth, enlarged bracts, shortened peduncles, wavy leaflets and stipulae. They were almost sterile, their pollen contained a variable proportion of empty grains and some anomalously large, small or deformed grains. In metaphase I, two extra chromosomes did not form a stable bivalent and only in some cases were situated close to each other. In anaphase I, the extra chromosomes migrated independently to either pole or retarded in the equatorial plain, the same was observed for chromatids in anaphase II. This retardation resulted in anomalous cytokinesis, so that triads, dyads and half-divided or non-divided monads appeared. The retarded extra chromosomes may form small extra nuclei either included into one of the microspores or forming a separate miniature cell; in this way tetrasomics may eliminate extra chromosomes. One of the tetrasomics analysed formed an exceptionally high proportion of microspore pentads. In the regluar TRUST-R trisomics, the sole extra chromosome retarded in the equatorial plain in anaphases I and II. The retardation in anaphase II often makes cytokinesis in trisomics (in general more regular than in tetrasomic) to proceed in two steps: at first cell wall formation separates a pollen mother cell into two dyads and then each of them into two microspores.     

Relationship of wild and cultivated forms of <Emphasis Type="Italic">Pisum</Emphasis> L. as inferred from an analysis of three markers,of the plastid,mitochondrial and nuclear genomes

Eighty-nine accessions of wild and cultivated peas (12 Pisum fulvum Sibth. et Smith., 7 P. abyssinicum A. Br., 31 wild and 42 cultivated forms of P. sativum L.) were analysed for presence of the variants of three functionally unrelated polymorphic markers referring to different cellular genomes. The plastid gene rbcL either contains or not the recognition site for restriction endonuclease AspLEI (rbcL+ vs. rbcL−); the mitochondrial gene cox1 either contains or not the recognition site for restriction endonuclease PsiI (cox1+ vs. cox1−); the nuclear encoded seed albumin SCA is represented by slow (SCA^S) or fast (SCA^F) variant. Most of the accessions possessed either of two marker combinations: 24 had SCA^F cox1+ rbcL+ (combination A) and 49 accessions had SCA^S cox1− rbcL− (combination B), 16 accessions represented 5 of the rest 6 possible combinations. All accessions of P. fulvum and P. abyssinicum had combination A, the overwhelming majority of cultivated forms of P. sativum had combination B while wild representatives of P. sativum had both combinations A and B, as well as rare combinations. This pattern indicates that combination A is the ancestral state in the genus Pisum L., inherited by P. fulvum and P. abyssinicum, while combination B seems to have arisen in some lineage of wild P. sativum which rapidly fixed mutational transitions of the three markers studied, most probably via a bottleneck effect during the Pleistocene. Then this ‘lineage B’ spread over Mediterranean and also gave rise to cultivated forms of P. sativum. Rare combinations may have resulted from occasional crosses between ‘lineage A’ and ‘lineage B’ in nature or during cultivation, or represent intermediate evolutionary lineages. The latter explanation seems relevant for an Egyptian cultivated form ‘Pisum jomardii Schrank’ (SCA^F cox1− rbcL−) which is here given a subspecies rank. Wild representatives of P. sativum could be subdivided in two subspecies corresponding to ‘lineage A’ and ‘lineage B’ but all available subspecies names seem to belong to lineage B only. Presently all wild forms would better be considered within a fuzzy paraphyletic subspecies P. sativum subsp. elatius (Bieb.) Schmalh. s. l.     

New data on three molecular markers from different cellular genomes in Mediterranean accessions reveal new insights into phylogeography of <Emphasis Type="Italic">Pisum sativum</Emphasis> L. subsp. <Emphasis Type="Italic">elatius</Emphasis> (Bieb.) Schmalh.

Twelve accessions classified as Pisum sativum subsp. elatius, mostly from West and Central Mediterranean, were analysed for three markers from different cellular genomes: rbcL (plastid genome), coxI (mitochondrial genome) and SCA (nuclear genome). Based on geographical distribution of their allele combinations analysed in this and the earlier study, we suggest a putative history of wild representatives of P. sativum. The ancestor of this species belonged to lineage A (coxI+, rbcL+, SCA ^f ); it appeared in East Mediterranean, then spread westward most probably during one of the Pleistocene coolings when the sea was smaller, so that representatives of lineage A remained in the Eastern Mediterranean and on the islands of Sicily and Menorca. Mutation leading to the loss of the restriction site for PsiI in coxI−, gave rise to lineage C (coxI−, rbcL+, SCA ^f ) which spread widely in the Mediterranean and is now found in France, Greece and Ethiopia. Mutation leading to rbcL− gave rise to lineage D (coxI−, rbcL−, SCA ^f ), now found in Egypt (P. sativum subsp. jomardii) and Spain. Mutational transition of SCA ^f to SCA ^s most probably took place in North-Eastern Mediterranean since the resulting lineage B (coxI−, rbcL−, SCA ^s ) now occupies the Tauro-Caucasian area. In Asia Minor and North Israel, line B met the ancestral line A so that both lines coexist there presently. The lineage B gave rise to the cultivated P. sativum subsp. sativum.