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To better understand how water stress and availability affect the enzyme activity and microbial communities in soil, we measured the changes of organic carbon (OC), bacteria and fungi populations, and endoglucanase and exoglucanase activities in a semiarid soil treated with air-dried primary sewage sludge at a rate of 20 g/kg. The water potentials established for soil incubation were: saturation (SA, 0 bar), field capacity (FC, -0.3 bar), and permanent wilting point (PWP, -15 bar). An irrigation treatment was a drying-rewetting cycle (DWC) between -0.3 to -15 bars. After 0, 20, 60 and 90 days of incubation soils were sampled for analysis. The addition of sewage sludge increased soil OC, endoglucanase and exoglucanase activities significantly. The effects of soil moisture, incubation time and their interactions on OC, and endoglucanase and exoglucanase activities in soil were significant. During 20 days of incubation, OC, endoglucanase and exoglucanase activities decreased significantly. Soils incubated in DWC and FC compared to soils incubated in SA and PWP had lower OC contents due to organic matter mineralization. Organic C, exoglucanase and endoglucanase activities significantly increased with increasing soil water potential. The activities of exoglucanase and endoglucanase in soils incubated in SA were significantly higher than those in soils incubated in PWP.

Soil microbial biomass is a dynamic force driving soil phosphorus cycling in soils. The temperature, time and method for killing soil organisms in soil biomass P determination are so important factors that affect the results. The aim of this study was to compare some methods of soil sterilization and soil microbial P (Pm) release in extraction with NaHCO₃. Five samples of calcareous soils in three replicates were incubated in field capacity and 28°C. The texture of soils differed from loamy sand to sandy loam. They had 10-15% equivalent calcium carbonate, 1-3% organic carbon and 40-90 mg/kg available P content. After 1, 10, 30, and 50 days of incubation a portion of each soil was sterilized by five methods (chloroform fumigation, autoclaving at 121°C for 0.5 h, oven drying at 70°C for 48 h, oven drying at 180°C for 2 h, and ultrasonification). Phosphorus of the sterilized and control soils were extracted with 0.5M NaHCO₃ (pH 8.5) and determined spectrophotometrically as blue molybdate-phosphate complexes under partial reduction with ascorbic acid. Results showed that the method of soil sterilization and soil type had significant effects on biomass P estimated in soils (P < 0.01). There were no significant differences between extracted biomass P at chloroform fumigation, autoclaving at 121°C for 0.5 h, and oven drying at 70°C for 48 h. However biomass P was significantly more extracted from soil by oven drying at 180°C for 2 h and by ultrasonification. Fixation of Pm in soil during the extraction period can reduce the precision of biomass P estimates. This effect was more obvious in biomass P determination by fumigation and oven drying at 70°C for 48 h. Biomass P determined by these methods and autoclaving had positive and significant correlations with soil sand contents, respectively due to long sterilization period and temperature. Ultrasonification released more P from these calcareous soils especially at the start of soil incubation. It released higher microbial P and reduced P sorption in soils; biomass P determined by this method compared to other methods had relatively higher correlations with fungi, glumales spore and P solubilizing bacteria numbers in soil.

Spring wheat var. Vánek was cultivated in pots in a soil naturally contaminated with heavy metals. Experimental plants were treated with three different types of brassinosteroids (BRs; 24-epibrassinolide, 24-epicastasterone and 4154) during two different growth stages 29-31 DC (off shooting) and 59-60 DC (beginning of anthesis). Content of heavy metals (Cu, Cd, Pb and Zn) was determined using AAS method in the plant growth stages 47-49 DC (visible awns), 73-75 DC (30-50% of final grain size) and 90-92 DC (full ripeness). At the stages 47-49 DC and 73-75 DC, the content of the heavy metals was determined in the biomass of whole plants, while at the stage 90-92 DC it was determined separately in straw and grains. After the treatment of plants with BRs a decrease in heavy metals content was observed in the growth stage 73-75 DC (i.e. during the period when the plants are harvested for ensilage purposes. Likewise, a decrease of lead content in the grains by 70-74% in the plants treated at both stages 29-31 DC and 59-60 DC and by 48-70% in the plants of the third group (plants treated at stage 59-60 DC) was determined as compared with the untreated plants.

It is evident that the presence of organic matters in soil considerably influences by its microbial oxidation to CO₂ the requirement for calcareous compounds as well as the necessary amelioration dose of lime to reduce incurred soil acidity as the impact of balanced buffering CO₂-HCO₃^- system, the more labile the organic matters are. If we take into consideration that the content of soil water per hectare of topsoil is, at the total weight of 6 × 10⁶ kg, approximately, in analyzed sandy-loam soils 1.2 × 10⁶ litre, in the given experiment soil water is just able to use up to 220 kg CaCO₃/ha for the fixation of free surplus CO₂ to the value of equilibrium CO₂, at zero elution! From this process, even 300-400 kg water-soluble Ca(HCO₃)₂ result. Of course, the ion exchange and the buffering system of the soil have further requirements for Ca compounds. Consequently, an unambiguous conclusion is: doses of calcareous compounds cannot be calculated only with the aim of reducing soil acidity and consumption of Ca nutrient by plants as it is common in the other nutrients. In a practical experiment in watersheds of nine Šumava brooks of the total area of 78.5 km² we studied changes in the stability of soil organic matters in the soils of these brooks in relation to variations in calcium carbonate equilibriums in waters from these watersheds in 1986-2004. The loss of the least stable fraction of soil organic matters, and the associated loss of the microbial activity of soils, were found to lead to a decrease in Langelier saturation index I_s in the waters, hence to a reduction in water corrosivity against CaCO₃, and so to a smaller need of liming to establish the calcium carbonate equilibrium in soil solutions even though exchange and active acidity of soil increased.

The effect of foliar application of kinetin on the growth and some physiological processes of pea plants growing in soil supplemented with 25 or 50µM Cd were studied. Cadmium treatment inhibited the growth rate, chlorophyll (Chl) content, net photosynthesis (P_N), content of soluble sugars and free amino acids of either shoots or roots. The application of kinetin (kin) enhanced the growth rate, Chl content, P_N, soluble sugars and free amino acids content of shoots and roots; dark respiration rate (R_D), contents of soluble protein and proline were increased by cadmium treatment. The addition of kinetin to Cd-stressed plant reduced R_D, soluble protein and proline content. Considerable variations in the content of Na⁺, K⁺, Ca²⁺ and Mg²⁺ were induced by Cd-treatments. Foliar application of kinetin exhibited a favorable effect on the accumulation of some ions and antagonized or ameliorated the inhibitory effect of Cd stress on some others.

Well-aerated and alkaline soils are proven to lack plant-available iron. Fe-efficient plants, however, induce morpho-physiological and biochemical mechanisms of adaptation. These changes in morphology and physiology of the shoot-root systems of peanut (Arachis hypogaea L. cv. NC 2) plants were studied by cultivating them hydroponically in the nutrient solution containing different levels of Fe³⁺EDDHA (0.00, 0.125, 0.25, 0.50, 1 and 2 ppm). Three types of chlorosis and regreening (I, II, III) on the shoot system appeared simultaneously with three types of rooting (I, II, III) in different stages of plant growth under Fe-free media. The difference in the regreening processes of plants grown in Fe-free and Fe-treated media indicated that their signaling pathways for Fe localization might be different. The morphological responses were found to correlate to three types of regular and rhythmic pH changes in the nutrient solutions. The sites of pH responses and Fe³⁺ reducing activities in the roots showed dependence on the type of root and shoot morphology.

The aim of the study was to determine the response of soil enzymes such as dehydrogenases, urease and acid and alkaline phosphatases to heating oil contaminating (0.0, 0.25, 0.5, 0.75, 1.0, 1.5% of soil) the experimental soil supplemented with lime and used for cultivation of yellow lupine of the Markiz variety. An increasing contamination of soil with heating oil stimulated the activity of dehydrogenases and acid and alkaline phosphatases but had a toxic effect on yellow lupine. Lime supplements did not have a significant effect on an average activity of soil dehydrogenases. However, such soil treatment had a significant effect on urease. Increasing heating oil doses in lime-supplemented soil stimulated urease activity, whereas in lime-free soil urease activity was inhibited. The activity of acid and alkaline phosphatase was lower in limed soil than in lime-free soil. The activity of dehydrogenases, urease and alkaline phosphatase in the soil with lupine cultivation was significantly higher than in the unsown soil.

The glutamate kinase activity was investigated as a plant stress response to Cd, Zn, As or sewage sludge application to soil in the pot and field experiments with spinach (Spinacia oleracea L.). Allosteric regulation of glutamate kinase activity by free proline creates a possibility for an increase in glutamic acid content due to the synthesis of glutathione and phytochelatines in plant cells. For this reason the high rates of As, Cd and Zn applied into soil strongly decreased the glutamate kinase activity. Allosteric regulation of the glutamate kinase activity did not inhibit the synthesis of proline and hydroxyproline under stress condition caused by organic pollutants after application of sewage sludge. Formed proline was bound to stress proteins and therefore glutamate kinase activity was not inhibited.

Soils were sampled from the plots with four variants of fertilisation: Nil - without fertilisation, NPK - mineral fertilisation, FYM - farmyard manure, FYM + NPK - farmyard manure with mineral fertilisation, and two variants of crop rotation: field IV - classical 9-year crop rotation, field B - 2-year rotation of alternative growing. Determination of urease, CFU of Azotobacter spp. and potential nitrogenase activity was conducted during the period 1999-2004. The urease activity was positively affected by manure fertilisation (FYM) and by the combination of FYM + NPK. The statistically significantly highest counts of Azotobacter spp. and the highest nitrogenase activity were determined on field B in variants FYM and FYM + NPK. The results show that there was a higher amount of accessible nitrogen present on field IV than on field B. This might explain the lower counts of Azotobacter spp. and therefore the lower nitrogenase activity. According to our results, activity of urease, CFU of Azotobacter spp. and potential nitrogenase activity are very closely connected with N inputs.

The CULTAN (Controlled Uptake Long Term Ammonium Nutrition) system is based on one-time injection of the whole dose of nitrogen required for the vegetation period. The effect of this method on yield and grain quality of winter wheat was observed in a 2-year small-plot trial at 4 different experimental sites in the Czech Republic. The experiment comprised two treatments with the total amount of nitrogen applied during fertilization of 150 kg N/ha. At the CULTAN treatment the whole dose was applied all at once using the GFI 3A injection machine (Maschinen und Antriebstechnik GmbH Güstrow), whereas at the control treatment, the dose was divided into three applications. The average grain yield of winter wheat in 2007 was 9.56 t/ha (control) and 8.78 t/ha (CULTAN); in 2008 it was 9.91 t/ha (control) and 9.63 t/ha (CULTAN). The differences in 2008 were not statistically significant. The contents of nitrogen and gluten were significantly lower at CULTAN treatment in both years. The values of falling number, Zeleny test and bulk density were generally similar at both treatments.

In this research cyanobacteria (Blue-Green Algae, BGA) were isolated, identified, multiplied and used as an inoculum in pot rice experiment. The pH, moisture and algal population were measured in four seasons. The highest and lowest pH (6.7, 6.2), moisture of soil (43%, 34%) and algal population (12, 20 Colony-Forming Units/50 ml on A and B medium and 4, 5 Colony-Forming Units/50 ml on A and B medium) were recorded in spring and winter, respectively. The only heterocystous cyanobacteria were found in soil samples identified as Anabaena with four species (A. spiroides, A. variabilis, A. torulosa and A. osillarioides). The germination of rice seeds treated with cyanobacteria was faster than control. The result of pot experiment were: increase of 53% in plant height; 66% in roots length; 58% in fresh leaf and stem weight; 80% in fresh root weight; 125% in dry leaf and stem weight; 150% in dry root weight; 20% in soil moisture; 28% in soil porosity and a decrease of 9.8% in soil bulk density and 4.8% in soil particle density. There were significant differences (P < 0.05) in pot treated with BGA as compared with control.

An incubation experiment with addition of EDTA and alfalfa into soils contaminated with heavy metal over 200 years was carried out in order to evaluate the EDTA effects on microbial properties. Alfalfa was added to soils together with EDTA to examine its abilities to improve microbial activities affected by EDTA. The obtained results showed that the addition of EDTA led to a significant decrease of microbial biomass C during the first 24 days of incubation. At the end of the experiment the microbial biomass C significantly increased quite close to the original level. The EDTA amendment caused, probably due to the toxic effects, a significant increase in respiratory activities and of the metabolic quotient qCO₂. An addition of alfalfa significantly improved the microbial biomass C contents in arable soils treated together with EDTA. Both, respiratory activities and qCO₂ significantly increased after the soil treatment with EDTA together with alfalfa. EDTA alone decreased the microbial biomass, alfalfa alone as organic substrate was mineralised and utilised by soil microorganisms for their metabolism.

Plant root and shoot dry weight, leaf relative water content (LRWC) and chlorophyll content were reduced by 30%, 21%, 15%, 34%, respectively, at 40mM NaCl as compared to non-salt stress conditions. However, membrane permeability (MP) of plant increased (85.0%) with increasing salinity. Foliar nutrient application (FNA) alleviated deleterious effects of salinity stress on growth and this effect was statistically significant. The highest alleviation effect of FNA at 40mM salinity stress was observed in the case of 10mM foliar KNO₃ and Ca(NO₃)₂ application, resulting in increase in plant root dry weight (50%), shoot dry weight (50%), LRWC (8.2%) and MP decrease (27.4%) at 40mM NaCl. Phosphorus, Fe and Zn contents in shoots and roots of plants also increased with FNA treatments, but they were still much lower than those of non-salt stress treatment. Sulphur, P, Fe and Zn contents of shoots reached similar values as in non-salt stress treatment when KNO₃ was applied, whereas Fe, Mn, Zn, and Cu contents of roots reached the values of non-salt stress treatment when Ca(NO₃)₂ was applied.

The objective of this study was to examine and demonstrate how harvesting age (flower age) contribute to the variations in the quality of Echinacea purpurea (L.) Moench. The effects of different flower developmental stages on caffeic acid derivatives and isobutylamide content are described. These phytochemicals were extracted from fresh plants with 60% ethanol and quantified by the HPLC analysis. The results revealed that the quality of Echinacea is strongly influenced by the flower developmental stages. The highest content of both hydrophilic and lipophilic components in the anthodium of Echinacea plants were found in the third (mature) developmental stage, which is regarded as the optimum one for the harvest to obtain optimum yield levels.

Dynamics of crop growth and photosynthesis are two main processes that are of major importance for adaptation of plants to their environment. Two experiments were carried out during 2005 and 2006 with sun and shaded barley plants. The results showed that leaf area increased with leaf position on the main stem up to leaf position 5 for sun and leaf position 6 for shaded plants, and then declined towards flag leaves. Air temperature affected leaf appearance, mainly at the beginning of the growing season. A positive correlation between leaf expansion duration (LED) and accumulated temperature sum was measured for both variants, LED linearly increased with temperature sum. Leaf expansion rate (LER) showed a similar dependence on accumulated air temperatures in both light variants. A strong relation was found between soil temperature and LER for the first four leaves of the main stem of shaded plants in 2006. In shaded environment the higher LER was associated with lower accumulated irradiance sum when light restriction supported an increase of leaf elongation and final leaf length.

The seeds of two medicinal plants, namely Chamomilla recutita (Babong) and Origanum majorana (Bardaqoush) were subjected to germination in different NaCl concentrations, polyamines (putrescine, spermidine, spermine) and to combination of both. The results revealed that the growth alterations induced by NaCl were alleviated by various levels of polyamines. The organic solutes of both plant seedlings exhibited somewhat variable responses to various salinity levels or polyamines treatments and in combination of both treatments. Putrescine in Ch. recutita seedlings was more effective in alleviating the stress effects of salinization than spermidine and spermine, while in O. majorana seedlings spermidine was more effective. Generally, the degree of stimulation differed according to the type, concentration of the additive used and the type of the plant tested.

This paper addressed the spatial distribution characteristics of organic matter, total nitrogen, extractable phosphorus and extractable potassium in agricultural soils of Northeast China. The related factors were explored using geostatistics and geographic information systems. The results showed that the log-transformed data of the four soil nutrients followed a normal distribution. Soil extractable phosphorus had a higher coefficient of variation. The experimental variogram of the log-transformed data of soil organic matter, total nitrogen and extractable phosphorus was fitted with an exponential model, while soil extractable potassium was fitted to a spherical model. Soil samples from smaller slope gradients had higher organic matter and total nitrogen. Soil type affected the four soil nutrients significantly. Soil samples from dry farming land had significantly higher total nitrogen and extractable potassium than soil from paddy fields, while the contrary was found for extractable phosphorus. Along the Yinma River, soil samples from the western part have statistically higher values for organic matter, total nitrogen and extractable potassium than those collected from the eastern part.

Changes in root anatomical structures at successive cycles of selection (cycle 1 to cycle 18, alternating) were observed in the study of maize (Zea mays L. cv. Saracura-BRS 4154) capable to survive and produce in temporarily flooded soils; this cultivars was developed by the Maize and Sorghum National Research Center through stratified phenotypic recurrent selection for cultivation wetland soils. Field trial was carried out and flooding of the soil was initiated at the six-leaf stage; the soil was flooded with water (20-cm deep) three times per week. Root sample was collected, fixed, and selected for observation in photon microscope. A gradual increase in the number of aerenchyma, the proportion of vascular cylinder, smaller metaxylem, and phloem and epidermis width, and a decrease in exodermis and cortex were observed in successive selection cycles. Such phenotypic changes impart the flood tolerance ability to this maize cultivar.

The effects of putrescine (a polyamine), low temperature and their combinations on the activities of apoplastic antioxidant enzymes were studied in the leaves of two wheat cultivars, winter (Dogu-88) and spring (Gerek-79). Fifteen-day-old wheat seedlings were treated with putrescine solutions (0.1, 1 and 10mM) prior to cold treatment (5/3°C). The activities of apoplastic catalase, peroxidase and superoxide dismutase were determined in the leaves both under normal and cold conditions at 1, 3 and 5 days. The results indicate that cold treatment significantly increased the activities of apoplastic catalase, peroxidase and superoxide dismutase in winter wheat while not generally affecting spring wheat. Under control conditions, the putrescine treatments were more effective in increasing the enzyme activities in winter wheat than in spring wheat. However, under cold conditions, the putrescine treatments surprisingly induced enzyme activities in spring wheat while generally reducing those in winter wheat leaves. The results show that putrescine may act as an agent inducing primary changes in the apoplastic antioxidant system of wheat leaves during reactive oxygen species-mediated damage caused by low temperature stress.

The heavy metal contents and their bioavailability were monitored in soils of Central Spiš region of SR. This area belongs to long term contaminated and hygienically loaded areas. Soil contamination by heavy metals is caused especially by ore mining, processing and treatment. Soil samples from the Central Spiš contained higher proportions of mobile forms which corresponded to the following sequence Pb > Zn > Cu, while for mobilizable forms the sequence of investigated metals was as follows: Cu > Zn > Pb. Soil pH is one of the parameters that affect significantly the share of bioavailable forms of metals. Higher proportions of mobile fractions of metals were detected in samples taken from soils with acidic pH. Statistical processing confirmed a relationship between the percentage share of lead and zinc in the mobile form and the level of pH/KCl, which was significant for Zn: r = -0.53. The relationships for lead and copper were insignificant.

The interaction of manganese with cadmium (Cd) toxicity was studied on maize plants grown in hydroponics. Manganese supplied as MnSO₄clearly alleviated the toxic effect of cadmium on the root growth of maize seedlings. The magnitude of alleviation was dose dependant and total abolition of 10µM Cd toxicity on root growth was observed at Mn/Cd ratio of 20:1. The 12 h pre-treatment with 10μM Cd was generally toxic for nitrate uptake and reduction (both determined in Cd-free media). The beneficial effect of 100μM Mn on this toxicity was confirmed for the low-affinity nitrate uptake system, but on the other hand, Mn alone seems to be slightly toxic for high affinity nitrate uptake system and on the nitrate reductase activity.

Skin scuffing is a problem of washing of the individual potato varieties, which is particularly important at harvests of physiologically immature tubers. Washing of such tubers cannot be recommended. Discoloration of scuffed tuber parts is another problem, which is exhibited by gray, brown to black color. Greening of washed tubers is mostly influenced by storage manner that also affects tuber sprouting. Mechanical damage, occurrence of several diseases, abiotic injuries, pest damages is also a problem. Various responses of potato varieties were found to tuber washing. Varieties with rough, netted skin, physiologically immature tubers, infected with diseases, mechanically damaged, susceptible to soft rot, expressing abiotic changes are not suitable for the washing. Tubers of varieties with smooth and bright skin, without scuffing, with later greening in the light, free of disease and abiotic injury presence and non-damaged by pests are suitable for washing. From this view the best results of tuber washing were obtained with varieties and hybrids: Adéla,Astoria, Belladonna, Dali, Ditta, Flavia, Futura, Katka, Kordoba, Kornelie, Lady Christl, Laura, Milva, Princess, Redstar, Rosara, Samantana, Satina, Secura, Velox,Vera,Victoria, KE 524-11, KE 12-83.

The uptake of As, Cd, Pb, and Zn and potential phytoremediation efficiency of five high biomass producing crops, white sweetclover (Melilotus alba L.), red clover (Trifolium pratense L.), curled mallow (Malva verticillata L.), safflower (Carthamus tinctorius L.) and hemp (Cannabis sativa L.) commonly used as grazing and/or energy crops was evaluated in both pot and field experiments at soils with different level of element contamination. In pot experiment the highest phytoremediation efficiency was demonstrated by C. tinctorius where 4.8% of Cd and 1.1% of Zn were removed from the moderately contaminated soil in one vegetation period when repeated harvest of aboveground biomass was performed. The removal of As and Pb was negligible for all the investigated plant species. At the highest element content in soil inhibition of plant growth due to the element phytotoxicity to plants was reported in most of cases. In the precise field experiment lower phytoremediation efficiency (biennial phytoremediation factors did not exceed 0.2% for Pb and Zn and 0.3% for Cd for C. tinctorius) was determined but yield suppress was not observed. Thus, free space for manipulation with element mobility in soil to increase element uptake by plants remains for further research.

A three-year field experiment was conducted from 2000 to 2002 in North-East Poland. Each year three sulphur fertilization rates in the form of sulphate (S-SO^2-₄) and pure (S-S⁰) sulphur were applied: 40, 80 and 120 kg/ha. In the soil horizon at the depth of 0-40 cm the triple rate of S- and S-S⁰) depressed soil reaction. Acidification of soil caused by S-SO^2-₄ became evident already in the first year of the study while that resulting from S-S⁰) application appeared as late as in the third year. The effect of sulphur on soil in the 40-80 cm horizon was irregular. As the sulphur rates increased and the duration of the experiment progressed, sulphates accumulated in soil. In the 0-40 cm soil layer, the increasing rates of sulphur tended to increase the content of N-NH⁺₄. In most objects, the NPK + S fertilization, and especially the single S-SO^2-₄ treatment, caused an increase in N-NO^-₃ in both soil layers compared with the NPK fertilized object. The dose of 120 kg/ha S-SO^2-₄ caused a significant increase in the concentration of available phosphorus in soil in the 0-40 and 40-80 cm layers.

The production of organic acids and changes during decomposition of rice straw amended with tricalcium phosphate (TCP) and Udaipur rock phosphate (URP) were studied under laboratory conditions. The organic C content of rice straw decreased and total N increased with time, resulting in a decrease in C:N ratio as the decomposition progressed. The pH decreased to acidic range in all the treatments on day 15, but became alkaline again later on. Soluble P increased at 15 days after incubation, declined later during decomposition, and was highest in the treatments containing TCP and Aspergillus awamori inoculation. Citric, oxalic, formic and maleic acids were detected during decomposition of rice straw and maximum amounts were present on day 15. Citric and oxalic acids were responsible mainly for P solubilization from TCP and URP; generally, citric acid was the most effective in P solubilization.

By reference to the Eternal Rye trial in Halle, Germany, as an example, it is demonstrated that long-term trials provide indispensable information for contemporary and future land use research. These trials serve as tools for the examination of cultivation measures or the effects of climate on nutrient dynamics and mobilization, microbial biodiversity, mineral composition or soil formation processes. They are therefore essential for the evaluation of land-use strategies or climatic change and, because of that, can provide more accuracy in related political considerations.

The paper deals with the possibilities of arsenic analysis in the soil. The aim is the selection and verification of the methods for analysis of As in the soil, which seem to be suitable for risk evaluation based on the increased As soil load. Economical and analytical availability of the methods is an important criterion. A sample set of 6 heavily contaminated soils was used to compare application potential of prevalent as well as less common procedures for determination of arsenic forms in soils. The results showed that substitution of analytically more demanding As total content analysis and sequential analysis for simple extraction using one-off agents seemed to be promising in many cases. The comparison and evaluation of statistical correlation of used methods of As analysis in the soil was realised. The results suggested that using the combination of simple 1M NH₄NO₃ extraction and determination procedure for amorphous Fe forms in the soil (the Tamm method) was suitable for the risk assessment stemming from the As contamination without necessity of the application of more complicated sequential extraction procedures.

The effects of different concentrations of copper (0-800 μmol) on growth, protein contents, peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and phenylalanine ammonia-lyase (PAL) in Jatropha curcas L. seedlings were assessed by means of pot experiments. Results suggested that increased copper concentrations lead to decreased shoot elongation and seedling biomass. Protein content in the leaves and roots reached their highest levels at the copper concentrations of 400 μmol, while the highest protein content in the stem was observed at 800 μmol copper. POD activity in leaves and stems was unaffected at low copper concentrations, but showed a considerable variation at high copper concentrations. In roots, the highest POD activity was observed at 200 μmol copper. Under copper stress, SOD activity in leaves increased concomitantly with increasing copper up to 400 μmol, and SOD activity in stems and roots showed a slight increase. Catalase activity significantly elevated in leaves and roots but showed no significant changes in stems of the seedlings exposed to copper. A gradual increase of PAL activity in leaves and roots at the copper concentration of 400 and 200 μmol was observed, while PAL activity remained unchanged in stems.

Significant quantities of Cd have been added to soils globally due to various anthropogenic activities, posing a serious threat to safe food production and human health. Rhizosphere, as an important interface of soil and plant, plays a significant role in the agro-environmental system. This article presents a review of relationship between root excretion and microorganisms and plant resistance to Cd toxicity and possible mechanisms. Root exudates markedly altered in species and quantity under Cd stress. Root exudates can affect Cd absorption by plants through changing the physical and chemical characteristics of rhizospheres. The influence of root exudates on Cd bioavailability and toxicity may include modifying the rhizosphere pH and Eh, chelating/complexing and depositing with Cd ions, and altering the community construction, the numbers and activities of rhizospheric microbes. In this paper, the methods to reduce the transfer of Cd in soil-plant system by adjusting rhizosphere environment are discussed, and some aspects are also proposed that should be emphasized in the future research work.