Effect of arsenic-contaminated irrigation water on growth and elemental composition of tomato and cabbage cultivated in three different soils, and related health risk assessment.

This study was carried out to determine the effect of arsenic on tomato and cabbage cultivated in sand, sandy silt, and silt soil, and irrigated with water containing arsenic at concentrations 0.05 and 0.2 mg/L. Increasing arsenic in irrigation water did not affect the photosynthetic machinery. The chlorophyll content index increased in case of all soils and was dependent on the soil nitrogen, phosphorous, and plant biomass. Arsenic concentrations of 0.05 and 0.2 mg/L did not display any phytotoxic symptoms other than reduction in biomass in some cases. In cabbage, arsenic treatment of 0.2 mg/L increased the overall plant biomass production, while in tomato there was a decrease in aerial part and fruit biomass. The biomass production of both plants treated with different concentrations of arsenic, in the three soils was in the following order: silt > sand > sandy silt. Increase of arsenic in the irrigation water resulted in increase in arsenic concentration in the root and aerial part of both plants, at the same cultivation parameters. But tomato fruits displayed a decrease in arsenic accumulation with higher arsenic treatment. In both plants, the arsenic concentration in the plant parts changed in the following order: root > aerial part > fruit. Cabbage accumulated approximately twenty-fold more arsenic in the edible part (0.10-0.25 mg/kg DW) as compared to tomato (0.006-0.011 mg/kg DW) and displayed a good correlation with soil extractable arsenic. When cabbage was cultivated in three different soils applying the same irrigation water, it accumulated arsenic in the following order: sand > sandy silt > silt (p < 0.001 at 0.05 mg/L and p < 0.01 at 0.2 mg/L arsenic treatment). In tomato, the difference in arsenic accumulation among different soil types was highly significant (p < 0.001) but the accumulation pattern varied with the arsenic treatment applied. Sandy soil with the lowest total soil arsenic (4.32 mg/kg) resulted in the highest arsenic concentration in both plants. Among all soils and plants, the transfer factors and bioaccumulation factors were higher in sandy soil, and in cabbage. The estimated daily intake and hazard quotient values for arsenic were lower than 1 in all cases, implying no non-cancerous health risks at the arsenic concentrations applied in our study. Among nutrients only P showed a slight decline with increasing arsenic concentration while all other elements (Mg, K, Ca, S, Si, Fe, Mn, Cu, Zn) did not display any significant changes.

Detection of plant cadmium toxicity by monitoring dielectric response of intact root systems on a fine timescale.

The root dielectric response was measured on a minute scale to assess its efficiency for monitoring short-term cadmium (Cd) toxicity non-destructively. Electrical capacitance (CR), dissipation factor (DR) and electrical conductance (GR) were detected during the 24 to 168 h after Cd treatment (0, 20, 50 mg Cd2+ kg-1 substrate) in potted maize, cucumber and pea. Stress was also evaluated by measuring leaf chlorophyll content, Fv/Fm and stomatal conductance (gs) in situ, and shoot and root mass and total root length after harvest. CR showed a clear diurnal pattern, reflecting the water uptake rate, and decreased significantly in response to excessive Cd due to impeded root growth, the reduced tissue permittivity caused by accelerated lignification, and root ageing. Cd exposure markedly increased DR, indicating greater conductive energy loss due to oxidative membrane damage and enhanced electrolyte leakage. GR, which was coupled with root hydraulic conductance and varied diurnally, was increased transiently by Cd toxicity due to enhanced membrane permeability, but declined thereafter owing to stress-induced leaf senescence and transpiration loss. The time series of impedance components indicated the comparatively high Cd tolerance of the applied maize and the sensitivity of pea cultivar, which was confirmed by visible shoot symptoms, repeated physiological investigations and biomass measurements. The results demonstrated the potential of single-frequency dielectric measurements to follow certain aspects of the stress response of different species on a fine timescale without plant injury. The approach can be combined with widely used plant physiological methods and could contribute to breeding crop genotypes with improved stress tolerance.

Monitoring of plant water uptake by measuring root dielectric properties on a fine timescale: diurnal changes and response to leaf excision.

BACKGROUND: The measurement of root dielectric response is a useful non-destructive method to evaluate root growth and function. Previous studies tracked root development throughout the plant growing cycle by single-time electrical measurements taken repeatedly. However, it is known that root conductivity and uptake activity can change rapidly, coupled with the day/night cycles of photosynthetic and transpiration rate. Therefore, the low-frequency dielectric monitoring of intact root-substrate systems at minute-scale temporal resolution was tested using a customized impedance measurement system in a laboratory environment. Electrical capacitance (CR) and conductance (GR) and the dissipation factor (DR) were detected for 144 h in potted maize, cucumber and pea grown under various light/dark and temperature conditions, or subjected to progressive leaf excision or decapitation. Photosynthetic parameters and stomatal conductance were also measured to evaluate the stress response. RESULTS: The CR and GR data series showed significant 24-h seasonality associated with the light/dark and temperature cycles applied. This was attributed to the diurnal patterns in whole-plant transpiration (detected via stomatal conductance), which is strongly linked to the root water uptake rate. CR and GR decreased during the 6-day dark treatment, and dropped proportionally with increasing defoliation levels, likely due to the loss of canopy transpiration caused by dark-induced senescence or removal of leaves. DR showed a decreasing trend for plants exposed to 6-day darkness, whereas it was increased markedly by decapitation, indicating altered root membrane structure and permeability, and a modified ratio of apoplastic to cell-to-cell water and current pathways. CONCLUSIONS: Dynamic, in situ impedance measurement of the intact root system was an efficient way of following integrated root water uptake, including diurnal cycles, and stress-induced changes. It was also demonstrated that the dielectric response mainly originated from root tissue polarization and current conduction, and was influenced by the actual physiological activity of the root system. Dielectric measurement on fine timescale, as a diagnostic tool for monitoring root physiological status and environmental response, deserves future attention.

Arsenic uptake and accumulation in bean and lettuce plants at different developmental stages.

The pattern of arsenic (As) uptake at different developmental stages in plants and its consequent influence on the growth of plants was investigated in bean and lettuce. Further, the human health risk from the consumption of these As-laced vegetables was determined. The irrigation water was contaminated with As at concentrations of 0.1, 0.25, and 0.5 mg/L. The As concentration in the plant parts (root, stem, leaves, and flower/fruit) was determined in bean at the young, flowering, and fruiting stages and lettuce at the young and mature stages. At the different growth stages, As had an impact on the biomass of bean and lettuce plant parts, but none of the biomass changes were significant (p>0.05). The increase in As concentration of the irrigation water elevated the As concentration of plant parts of both plants at all growth stages, with the exception of the bean fruit. The As concentration in the developmental stages was in the order: lettuce (young>mature) and bean (fruiting>young>flowering). In lettuce, the transfer factor was higher at the young stage (0.09-0.19, in the control and 0.1 mg/L As treatment), while in bean, it was highest at the flowering stage (0.09-0.41, in all treatments). In the edible part, lettuce possessed substantially elevated As concentrations (0.30, 0.61, and 1.21 mg/kg DW) compared to bean (0.008, 0.005, and 0.022 mg/kg DW) at As treatments of 0.1, 0.25, and 0.5 mg/L, respectively, and posed significant health risks at all applied As concentrations.

Soil biological activity after a sixty-year fertilization practice in a wheat-maize crop rotation.

This study aimed to survey the long-term effects of fertilization practices on the functional diversity of the soil microbiota. A 60-year fertilization experiment with mineral fertilizers, farmyard manure and combined treatments was sampled in two consecutive years in maize (Zea mays L.) and wheat (Triticum aestivum L.). Soil chemical properties, plant growth and physiological parameters were measured. The MicroRespTM method was applied to assess the community level physiological profiles (CLPPs) of the rhizosphere soil, and the arbuscular mycorrhizal fungal (AMF) colonization of the roots was determined. Samples were taken in the early vegetative stages, at flowering, and at harvest in both years. The measured parameters were analysed using multifactorial ANOVA to determine treatment effects, crop-dependent differences, and seasonality. PCA analysis was performed on the data matrix to reveal more complex correspondences, and Pearson's product-moment correlation was used to confirm relationships between some of the measured soil and plant parameters. Fertilization treatments caused long-term changes in some biological parameters such as: MicroRespTM parameters, citrate utilization, total substrate-induced respiration value, and the ratio of utilization of amino acids and sugars. The rate of AMF colonization responded mainly to the plant nutrition status and the plant requirements, suggesting a plant-mediated effect in the case of mycorrhiza. Mineral nitrogen fertilization and soil acidification were found to be the main factors affecting the catabolic activity of soil microbiota, while AMF colonization responded to the balance of plant nutrition.

Electrical Capacitance versus Minirhizotron Technique: A Study of Root Dynamics in Wheat-Pea Intercrops.

This study evaluated the concurrent application and the results of the root electrical capacitance (CR) and minirhizotron (MR) methods in the same plant populations. The container experiment involved three winter wheat cultivars, grown as sole crops or intercropped with winter pea under well-watered or drought-stressed conditions. The wheat root activity (characterized by CR) and the MR-based root length (RL) and root surface area (RSA) were monitored during the vegetation period, the flag leaf chlorophyll content was measured at flowering, and the wheat shoot dry mass (SDM) and grain yield (GY) were determined at maturity. CR, RL and RSA exhibited similar seasonal patterns with peaks around the flowering. The presence of pea reduced the maximum CR, RL and RSA. Drought significantly decreased CR, but increased the MR-based root size. Both intercropping and drought reduced wheat chlorophyll content, SDM and GY. The relative decrease caused by pea or drought in the maximum CR was proportional to the rate of change in SDM or GY. Significant linear correlations (R2: 0.77-0.97) were found between CR and RSA, with significantly smaller specific root capacitance (per unit RSA) for the drought-stress treatments. CR measurements tend to predict root function and the accompanying effect on above-ground production and grain yield. The parallel application of the two in situ methods improves the evaluation of root dynamics and plant responses.

Effect of Se-Enriched Irrigation Water on the Biomass Production and Elemental Composition of Green Bean, Cabbage, Potato and Tomato.

Additional Selenium (Se) intake may be recommended in areas of Se deficiency to prevent various human diseases. One possibility for this is biofortification. In this experiment, the effect of irrigation water containing 100 and 500 µg L-1 Se, in the form of Na2SeO4, on green bean, cabbage, potato and tomato was investigated in a greenhouse pot experiment with sand, silty sand and silt soils. The chlorophyll content index was usually improved by Se and was significantly higher in potato in sand and silty sand and in tomato in silty sand and silt soils. The Se content of edible plant parts increased 63-fold in the 100 µg L-1 Se treatment and almost 400-fold in the 500 µg L-1 Se treatment, averaged over the four species and the three soils. Irrigation water with a Se content of 100 µg L-1 may be suitable for the production of functional food in the case of green beans, potatoes and tomatoes. However, due to its greater Se accumulation, cabbage should only be irrigated with a lower Se concentration. The use of Se-enriched irrigation water might be a suitable method for Se biofortification without a significant reduction in plant biomass production and without a remarkable modification of other macro- and microelement contents.

Effect of the Boron Concentration in Irrigation Water on the Elemental Composition of Edible Parts of Tomato, Green Bean, Potato, and Cabbage Grown on Soils With Different Textures.

The most important environmental source of boron (B) contamination is irrigation water. The data on the effect of B on the elemental composition in the edible parts of vegetables are scarce. A greenhouse pot experiment investigated the effect of irrigation water containing 0.1 and 0.5 mg/L B on the biomass, elemental (e.g., B, Mg, K, Fe, Cu, and Zn) composition, and photosynthetic parameters of tomato (Solanum lycopersicum), green bean (Phaseolus vulgaris), potato (Solanum tuberosum), and cabbage (Brassica oleracea) plants grown on 10 kg of sand, silty sand, or silty soil. The biomass of the edible part was unaffected by B treatment. The soil type determined the effect of B irrigation on the elemental composition of vegetables. The B content increased by 19% in tomatoes grown on silty soil. The 0.1 mg/L B treatment facilitated tomato fruit ripening on all soils, and the 0.5 mg/L B treatment doubled its chlorophyll content index (CCI) on silty soil. The 0.5 mg/L B treatment negatively affected the nutritional value of green beans on all soils, decreasing the Fe and K contents by an average of 83 and 34%, respectively. The elemental composition of potato was unaffected by the treatments, but the CCI of potato leaves increased in the 0.5 mg/L B treatment by 26%. The B content was increased by 39% in cabbages grown on light-textured soils. In conclusion, B concentration of up to 0.5 mg/L in irrigation water had no significant beneficial or adverse effect on the investigated vegetables, but 0.1 mg/L B treatment could shorten tomato fruit maturation time on B-poor soils. The B levels in vegetables remained suitable for human consumption.

Density and Diversity of Microbial Symbionts under Organic and Conventional Agricultural Management.

The influence of organic and conventional farming and agroecology on the diversity and functioning of indigenous soil microbial communities was examined using a multifactorial analysis based on an extended minimum data set of classical status and functional tests. Main soil physicochemical properties and selected microbiological indicators, the quantity of heterotrophic or aerobic spore-forming bacteria, basal and substrate-induced respiration, catabolic activity with MicroResp™, and fluorescein diacetate enzyme activity were characterized. A pot experiment applying the most probable number method was designed with soil dilution series using Pisum sativum L. and Triticum spelta L. to assess the symbiotic infectivity and genetic diversity of key indicator groups of the plant microbiome, e.g. nitrogen-fixing bacteria (rhizobia) and arbuscular mycorrhizal fungi. Soil pH, humus content, CFU, enzyme activity, and soil respiration were significantly higher in organic soils. The activity of soil microorganisms was mainly related to clay, humus, calcium, and magnesium parameters. A redundancy analysis test of catabolic activities showed that samples were grouped according to different substrate utilization patterns and land uses were also clearly separated from each other. Farming practice influenced the abundance and diversity of microbial populations. Dark septate endophytic fungi were only found in conventional soils. In addition to confirming soil health improvements by organic management, our results highlight the importance of a complex evaluation including both classical status and functional parameters of soil microbiota, which may more reliably indicate a shift in the quality status of soils.

Symbiotic Effectivity of Dual and Tripartite Associations on Soybean (Glycine max L. Merr.) Cultivars Inoculated With Bradyrhizobium japonicum and AM Fungi.

Soybean (Glycine max L. Merr.) is regarded worldwide as indisputably one of the most important crops for human food and animal feed. The presence of symbiotic bacteria and fungi is essential for soybean breeding, especially in low-input agricultural systems. Research on the cooperation between different microbial symbionts is a key to understanding how the health and productivity of the plant is supported. The symbiotic effectivity of dual and tripartite symbiotic agents was investigated in two pot experiments on different soybean cultivars with special regard to compatibility. In the Selection experiment, two out of sixteen soybean cultivars (Aliz, Emese) were chosen on the basis of their drought tolerance and used in all the other investigations. In the Compatibility experiment, the compatible coupling of symbiotic partners was selected based on the efficiency of single and co-inoculation with two Bradyrhizobium japonicum strains and two commercial arbuscular mycorrhizal fungal (AMF) products. Significant differences were found in the infectivity and effectivity of the microsymbionts. The rhizobial and AMF inoculation generally improved plant production, photosynthetic efficiency and root activity, but this effect depended on the type of symbiotic assotiation. Despite the low infectivity of AMF, inocula containing fungi were more beneficial than those containing only rhizobia. In the Drought Stress (DS) experiment, co-inoculated and control plants were grown in chernozem soil originating from organic farms. Emese was more resistant to drought stress than Aliz and produced a bigger root system. Under DS, the growth parameters of both microbially inoculated cultivars were better than that of control, proving that even drought tolerant genotypes can strengthen their endurance due to inoculation with AMF and nitrogen fixing bacteria. Root electrical capacitance (CR) showed a highly significant linear correlation with root and shoot dry mass and leaf area. The same root biomass was associated with higher CR in inoculated hosts. As CR method detects the absorptive surface increasing due to inoculation, it may be used to check the efficiency of the microbial treatment.

Application of Electrical Capacitance Method for Prediction of Plant Root Mass and Activity in Field-Grown Crops.

The root electrical capacitance (C R ) method is suitable for assessing root growth and activity, but soil water content (SWC) strongly influences the measurement results. This study aimed to adapt the method for field monitoring by evaluating the effect of SWC on root capacitance to ensure the comparability of C R detected at different SWC. First a pot experiment was conducted with maize and soybean to establish C R -SWC functions for the field soil. Ontogenetic changes in root activity were monitored under field conditions by simultaneously measuring C R and SWC around the roots. The C R values were normalized using SWC data and experimental C R -SWC functions to obtain C R*, the comparable indicator of root activity. The effect of arbuscular mycorrhizal fungi (AMF) inoculation on the C R* and biomass of field-grown soybean was investigated. The pot trial showed an exponential increase in C R with SWC. C R -SWC functions proved to be species-specific. C R showed strong correlation with root dry mass (R2 = 0.83-0.87). The root activity (C R*) of field-grown crops increased until flowering, then decreased during maturity. This was consistent with data obtained with other methods. AMF inoculation of soybean resulted in significantly higher C R* during the late vegetative and early flowering stages, when destructive sampling concurrently showed higher shoot biomass. The results demonstrated that the root capacitance method could be useful for time course studies on root activity under field conditions, and for comparing single-time capacitance data collected in areas with heterogeneous soil water status.

Effect of Arbuscular Mycorrhizal Fungi on the Growth and Polyphenol Profile of Marjoram, Lemon Balm, and Marigold.

The aim of this study is to examine the effect of arbuscular mycorrhizal fungi (AMF) colonization on biomass, polyphenol profile, and content of economically important herbs. A pot experiment was performed with marjoram, lemon balm, and marigold applying a commercially available AMF mixture for inoculation. Major polyphenols were identified using HPLC-UV-ESI-qTOFMS on the basis of their UV-vis and mass spectral characteristics, and selected ones were quantified. We showed that AMF can provide different services for each herb. Marjoram had the highest level of fungal colonization (82 M%) followed by lemon balm (62 M%) and marigold (17 M%). AMF inoculation significantly increased the biomass of marjoram (1.5-fold), the number of marigold flowers (1.2-fold), and the yield of rosmarinic acid and lithospermic acid isomers of marjoram (1.5-fold) and lemon balm (1.2-fold). Therefore, the quantity and quality of plant material could be improved by the application of optimized AMF inoculum.

Estimation of AM fungal colonization - Comparability and reliability of classical methods.

The characterization of mycorrhizal status in hosts can be a good indicator of symbiotic associations in inoculation experiments or in ecological research. The most common microscopic-based observation methods, such as (i) the gridline intersect method, (ii) the magnified intersections method and (iii) the five-class system of Trouvelot were tested to find the most simple, easily executable, effective and objective ones and their appropriate parameters for characterization of mycorrhizal status. In a pot experiment, white clover (Trifolium repens L.) host plant was inoculated with 6 (BEG144; syn. Rhizophagus intradices) in pumice substrate to monitor the AMF colonization properties during host growth. Eleven (seven classical and four new) colonization parameters were estimated by three researchers in twelve sampling times during plant growth. Variations among methods, observers, parallels, or individual plants were determined and analysed to select the most appropriate parameters and sampling times for monitoring. The comparability of the parameters of the three methods was also tested. As a result of the experiment classical parameters were selected for hyphal colonization: colonization frequency in the first stage or colonization density in the later period, and arbuscular richness of roots. A new parameter was recommended to determine vesicule and spore content of colonized roots at later stages of symbiosis.

Mycorrhizal symbiosis effects on growth of chalk false-brome (Brachypodium pinnatum) are dependent on the environmental light regime.

AMF (arbuscular mycorrhizal fungi) colonization of the grass chalk false-brome (Brachypodium pinnatum (L.) P. B.) was studied in selected habitats under spatially different light regimes: (a) shade condition under oak trees, (b) half shade in a shrubby area and (c) full-sun conditions on unshaded grassland. This study assessed the variations in AMF colonization of the grass dependent on the light supply in field habitats. Soil, root and shoot samples were collected four times during the vegetation period (in June, July, September and October). Root colonization, root and shoot biomass as well as soil water content were determined. The highest rate of AMF colonization was detected in June under half-sun and full-sun conditions, where about 50% of the roots were colonized. The average amount of arbuscules was less than 20% in the roots at the three sites, with the highest number of arbuscules in June, under half-sun and full-sun conditions, however, not under the trees. Overall, best mycorrhizal colonization occurred during summer, and its rate decreased in autumn. This tendency inversely correlated with the amount of precipitation, and thus with the water content of soils. The high colonization rate of the examined root samples, and also its seasonal fluctuation, might reflect the importance of the symbiosis where inorganic nutrients and water are the growth-limiting factors. The marginal AMF colonization of chalk false-brome under shade conditions indicates that plants do not use AMF under all stress conditions. When low light limits photosynthesis and thus growth of the plants, they dispense with the colonization of AMF in order to save the expenditure of organic carbon.

Metabolic activity and genetic diversity of microbial communities inhabiting the rhizosphere of halophyton plants.

A preliminary study was conducted to compare the community level physiological profile (CLPP) and genetic diversity of rhizosphere microbial communities of four plant species growing nearby Kiskunság soda ponds, namely Böddi-szék, Kelemen-szék and Zab-szék. CLPP was assessed by MicroResp method using 15 different substrates while Denaturing Gradient Gel Electrophoresis (DGGE) was used to analyse genetic diversity of bacterial communities. The soil physical and chemical properties were quite different at the three sampling sites. Multivariate statistics (PCA and UPGMA) revealed that Zab-szék samples could be separated according to their genetic profile from the two others which might be attributed to the geographical location and perhaps the differences in soil physical properties. Böddi-szék samples could be separated from the two others considering the metabolic activity which could be explained by their high salt and low humus contents. The number of bands in DGGE gels was related to the metabolic activity, and positively correlated with soil humus content, but negatively with soil salt content. The main finding was that geographical location, soil physical and chemical properties and the type of vegetation were all important factors influencing the metabolic activity and genetic diversity of rhizosphere microbial communities.

Drought, but not salinity, determines the apparent effectiveness of halophytes colonized by arbuscular mycorrhizal fungi.

The halophytes Plantago maritima, Aster tripolium, Artemisia santonicum, Puccinellia limosa, Festuca pseudovina and Lepidium crassifolium from two different saline soils of the Hungarian steppe were examined for colonization by arbuscular mycorrhizal fungi (AMF). The salt aster (A. tripolium) and the sea plantain (P. maritima) were examined more thoroughly by recording root colonization parameters, the salt content in the soil and monthly precipitations in 2001 and 2002. Mycorrhizal colonization was maximal in late spring to early summer and had a second peak later in the autumn. Arbuscule formation and overall mycorrhizal colonization appeared to be inversely correlated with the intensity of rainfall at the investigated sites. The results suggest that, in addition to seasonality, drought may play an important role in governing mycorrhizal activity in saline habitats. In greenhouse experiments, conditions in which AMF could overcome the inhibitory effects of sodium chloride on establishing plant-mycorrhizal symbiosis were not met.