Dominik Vodnik

EDTA enhanced heavy metal phytoextraction : metal accumulation, leaching and toxicity

Synthetic chelates such as ethylene diamine tetraacetic acid (EDTA) have been shown to enhance phytoextraction of some heavy metals from contaminated soil. In a soil column study, we examined the effect of EDTA on the uptake of Pb, Zn and Cd by Chinese cabbage (Brassica rapa), mobilization and leaching of heavy metals and the toxicity effects of EDTA additions on plants. The most effective was a single dose of 10 mmol EDTA kg−1 soil where we detected Pb, Zn and Cd concentrations that were 104.6, 3.2 and 2.3-times higher in the aboveground plant biomass compared to the control treatments. The same EDTA addition decreased the concentration of Pb, Zn and Cd in roots of tested plants by 41, 71 and 69%, respectively compared to concentrations in the roots of control plants. In columns treated with 10 mmol kg−1 EDTA, up to 37.9, 10.4 and 56.3% of initial total Pb, Zn and Cd in soil were leached down the soil profile, suggesting high solubility of heavy metals-EDTA complexes. EDTA treatment had a strong phytotoxic effect on the red clover (Trifolium pratense) in bioassay experiment. Moreover, the high dose EDTA additions inhibited the development of arbuscular mycorrhiza. The results of phospholipid fatty acid analyses indicated toxic effects of EDTA on soil fungi and increased environmental stress of soil microfauna.

Photosynthetic performance of vegetative and reproductive structures of green hellebore (Helleborus viridis L. agg.)

Photosynthetic irradiance response of vegetative and reproductive structures of the green-flowered deciduous perennial green hellebore was studied by the comparative use of chlorophyll (Chl) fluorescence techniques and gas exchange measurements. All the Chl-containing organs (leaves, sepals, stalks, and fruits) examined were photosynthetically active showing high intrinsic efficiencies of photosystem 2 (Fv/Fm: 0.75–0.79) after dark adaptation. Even in the smaller fertile and sterile parts of the flower (nectaries and anthers) a remarkable photosynthetic competence was detected. With increasing photon flux densities (PFD) electron transport rates, actual quantum yields, and photochemical quenching coefficients of the main photosynthetic organs decreased in the order: leaf>sepal>fruit>stalk. At moderate to high PFDs the sepals achieved maximum electron transport rates corresponding to about 80 % of concomitant mature leaves. In contrast, maximum net photosynthetic rate of the sepals [2.3 μmol(CO2) m−2 s−1] were less than one fourth of the leaves [10.6 μmol(CO2) m−2 s−1]. This difference is explained by a 70–80 % lower stomatal density of sepals in comparison to leaves. As the basal leaves emerge late during fruit development, the photosynthetically active sepals are a major source of assimilates, contributing more than 60 % of whole-plant CO2 gain in early spring. The ripening dehiscent fruits are characterized by an effective internal re-fixation of the respirational carbon loss and thus additionally improve the overall carbon budget.

Local Adaptation to Soil Hypoxia Determines the Structure of an Arbuscular Mycorrhizal Fungal Community in Roots from Natural CO2 Springs

ABSTRACT The processes responsible for producing and maintaining the diversity of natural arbuscular mycorrhizal (AM) fungal communities remain largely unknown. We used natural CO2 springs (mofettes), which create hypoxic soil environments, to determine whether a long-term, directional, abiotic selection pressure could change AM fungal community structure and drive the selection of particular AM fungal phylotypes. We explored whether those phylotypes that appear exclusively in hypoxic soils are local specialists or widespread generalists able to tolerate a range of soil conditions. AM fungal community composition was characterized by cloning, restriction fragment length polymorphism typing, and the sequencing of small subunit rRNA genes from roots of four plant species growing at high (hypoxic) and low (control) geological CO2 exposure. We found significant levels of AM fungal community turnover (β diversity) between soil types and the numerical dominance of two AM fungal phylotypes in hypoxic soils. Our results strongly suggest that direct environmental selection acting on AM fungi is a major factor regulating AM fungal communities and their phylogeographic patterns. Consequently, some AM fungi are more strongly associated with local variations in the soil environment than with their host plants distribution.

Inoculation ofRhododendron cv. Belle-Heller with two strains ofPhialocephala fortinii in two different substrates

The growth response of an ornamentalRhododendron hybrid to the inoculation withPhialocephala fortinii was studied in two pot experiments in order to decide about the effectiveness of the inoculation of young rhododendron microplants. Two different substrates were used in both experiments, either sterilized or non-sterilized: a horticultural substrate and a soil collected from a field site with dominant ericoid vegetation. Two fungal isolates were used for an inoculation:P. fortinii strain P (UAMH 8433) andP. fortinii strain F, a dark septate endophyte (DSE) previously isolated from naturally-infected roots ofVaccinium myrtillus. BothPhialocephala strains successfully colonized the roots of the host plants forming typical DSE (=pseudomycorrhizal) colonization pattern including the formation of intracellular microsclerotia. However, pseudomycorrhizal colonization did not affect the growth parameters of the host rhododendrons. The results from both experiments indicate a neutral effect of the inoculation with DSE fungi on the growth ofRhododendron cv. Belle-Heller.

Effect of EDTA washing of metal polluted garden soils. Part II: Can remediated soil be used as a plant substrate?

In a field experiment on metal contaminated and EDTA-remediated soil we studied plant performance, mycorrhizal associations and prospects of potential re-use of remediated soil as a garden substrate. Two experimental plots of 4 × 1 × 0.3 m were filled, one with remediated and the other with original contaminated soil. Selected cultivars were rotated over the course of 16months. Pb, Zn, Cd and micronutrient plant uptake was measured and their phytoaccessibility was analyzed by the DTPA method. Plant fitness was assessed by chlorophyll fluorescence and gas exchange measurements and evaluation of root colonization were analyzed with mycorrhizal fungi. Remediation reduced Pb and Cd concentrations in roots, green parts and fruits in most of the plants. Phytoaccumulation of Zn was reduced in one half of the cultivars. Some plants suffered from Mn deficiency as total soil Mn was reduced 4-fold and phytoaccessibility of micronutrients Cu, Fe and Mn for 54, 26 and 79%, respectively. Plant biomass was reduced. Photosynthetic parameters of plants grown in original and remediated soil were similar, except for the reduction in Spinacia oleracea. The frequency of mycorrhizal colonization in the roots of Pisum sativum was reduced five-fold and no significant changes were found in Allium cepa roots. Remediation reduced plant uptake of Pb below the concentration stipulated by legislation. Measures to reduce plant accumulation of other toxic metals and to revitalize remediated soil are needed.

Photosynthesis of Cockspur [Echinochloa crus-galli (L.) Beauv.] at Sites of Naturally Elevated CO2 Concentration

High abundance of cockspur (Echinochloa crus-galli) at the geothermal carbon dioxide spring area in Stavešinci indicates that this species is able to grow under widely varying CO2 concentrations. Living cockspur plants can even be found very close to gas-releasing vents where growth is significantly reduced. Plant height correlated well with CO2 exposure. The δ13C value of the CO2 spring air was −3.9 ‰ and δ13C values of high-, medium-, and low-CO2 plants were −10.14, −10.44, and −11.95 ‰, respectively. Stomatal response directly followed the prevailing CO2 concentrations, with the highest reduction of stomatal conductance in high CO2 concentration grown plants. Analysis of the curves relating net photosynthetic rate to intercellular CO2 concentration (PN-Ci curves) revealed higher CO2 compensation concentration in plants growing at higher CO2 concentration. This indicates adjustment of respiration and photosynthetic carbon assimilation according to the prevailing CO2 concentrations during germination and growth. There was no difference in other photosynthetic parameters measured.

Lead uptake by Picea abies seedlings: Effects of nitrogen source and mycorrhizas

Summary Heavy metals, and particularly lead (Pb), have accumulated in the humic layer of forest soils in Central Europe and North America. Among other environmental factors, rhizosphere pH and mycorrhizas have the potential of modifying heavy metal uptake of forest trees and, thus, heavy metal stress. To investigate the influence of rhizosphere pH and mycorrhizas on Pb uptake, we grew Norway spruce seedlings, non-mycorrhizal or ectomycorrhizal with Laccaria bicolor or Paxillus involutus in root boxes in a quartz sand/nutrient solution culture system. The seedlings were supplied with NH 4 NO 3 -N or NO 3 -N for 6 weeks. During the last 3 weeks, 5 μM lead (Pb) was added to the nutrient solution. The pH at the rhizoplane of short roots measured with antimony microelectrodes was higher with NO 3 − nutrition than with NH 4 NO 3 nutrition. In shoots, no Pb was detected. Total Pb in roots was reduced by mycorrhizal infection but was not affected by the N source. The portion of Pb that could be desorbed from roots by washes in 5 mM CaCl 2 or 0.4 mM HCl was 47 or 10%, respectively. This portion comprised mainly apoplastic Pb and was neither affected by the N source nor by the presence of mycorrhiza. Mycorrhizal infection had no effect on the pH at the rhizoplane. The element content of semi-thin sections of mycorrhizal or non-mycorrhizal short roots was examined with X-ray microanalysis. The Ca and Mg contents in the cortex cell walls of both mycorrhizal and non-mycorrhizal seedlings were strongly increased with NO 3 − nutrition, indicating a higher cation exchange capacity of the cortex apoplast with NO 3 − nutrition. Despite of the higher binding capacity of the cortex cell walls, the Pb content was lower with NO3- nutrition than with NH 4 NO 3 nutrition. In addition, the Pb content in the stele was also reduced with NO 3 − nutrition. Mycorrhizal infection had no effect on the Pb content of cell walls in the cortex and stele. In an accompanying solution culture experiment conducted under similar conditions, increased solution pH (pH 5 vs. pH 3.2) had a similar effect on Pb contents in root cortex cell walls as had NO 3 − nutrition in the sand culture experiment. We conclude that in forest ecosystems where NO 3 − is the main N source, increased rhizosphere pH may reduce Pb uptake into the root cortex.

Bimodal dynamics of primary metabolism-related responses in tolerant potato-Potato virus Y interaction

BackgroundPotato virus Y (PVY) is a major pathogen that causes substantial economic losses in worldwide potato production. Different potato cultivars differ in resistance to PVY, from severe susceptibility, through tolerance, to complete resistance. The aim of this study was to better define the mechanisms underlying tolerant responses of potato to infection by the particularly aggressive PVYNTN strain. We focused on the dynamics of the primary metabolism-related processes during PVYNTN infection.ResultsA comprehensive analysis of the dynamic changes in primary metabolism was performed, which included whole transcriptome analysis, nontargeted proteomics, and photosynthetic activity measurements in potato cv. Désirée and its transgenic counterpart depleted for accumulation of salicylic acid (NahG-Désirée). Faster multiplication of virus occurred in the NahG-Désirée, with these plants developing strong disease symptoms. We show that while the dynamics of responses at the transcriptional level are extensive and bimodal, this is only partially translated to the protein level, and to the final functional outcome. Photosynthesis-related genes are transiently induced before viral multiplication is detected and it is down-regulated later on. This is reflected as a deficiency of the photosynthetic apparatus at the onset of viral multiplication only. Interestingly, specific and constant up-regulation of some RuBisCO transcripts was detected in Désirée plants, which might be important, as these proteins have been shown to interact with viral proteins.In SA-deficient and more sensitive NahG-Désirée plants, consistent down-regulation of photosynthesis-related genes was detected. A constant reduction in the photochemical efficiency from the onset of viral multiplication was identified; in nontransgenic plants this decrease was only transient. The transient reduction in net photosynthetic rate occurred in both genotypes with the same timing, and coincided with changes in stomatal conductivity.ConclusionsDown-regulation of photosynthesis-related gene expression and decreased photosynthetic activity is in line with other studies that have reported the effects of biotic stress on photosynthesis. Here, we additionally detected induction of light-reaction components in the early stages of PVYNTN infection of tolerant interaction. As some of these components have already been shown to interact with viral proteins, their overproduction might contribute to the absence of symptoms in cv. Désirée.

Influence of nitrogen on leaf chlorophyll content and photosynthesis of ‘Golden Delicious’ apple

Abstract The aim of the present study was to estimate the influence of different rates of soil-applied nitrogen on leaf N and chlorophyll content and photosynthesis in ‘Golden Delicious’ apple trees. Three different treatments were included: the trees were either fertilized with 80 kg N ha−1 (N-80), 250 kg N ha−1 (N-250) or left unfertilized (CON). Fertilization increased leaf nitrogen content, with a more prominent effect in high N application level treatment. In all treatments, a slight seasonal decrease in leaf nitrogen content was observed. N-250 treatment resulted in higher chlorophyll content; a similar effect was found late in the season for N-80 treatment. Measurements of A-C i curves, performed on spur leaves, revealed a higher CO2 saturated photosynthetic rate in N-250 trees compared with low application level fertilized or unfertilized trees. No effect of N fertilization on carboxylation efficiency was found, as revealed by comparisons of the initial slopes of A-C i curves. The lack of positive effect is rather surprising, since the leaf N content was efficiently increased with application of fertilizer. Obviously, the existing pool of leaf nitrogen in non-fertilized trees does not limit Rubisco activity and efficiency.

The Effects of Natural CO2 Enrichment on the Growth of Maize

SUMMARY Maize plants (Zea mays) were grown in a field influenced by a geothermal source of CO2 (CO2 spring Stavešinci, Slovenia). Yield parameters and the content of photosynthetic pigments, mineral nutrients, antioxidants and soluble sugars were measured and the photo-synthetic performance was followed in plants growing at different CO2 conditions. Growth parameters were negatively correlated with the soil CO2 concentration as measured at 20 cm depth. Analysis of A-Ci curves revealed lower maximum photosynthesis (CO2-saturated photosynthesis) and lower carboxylation efficiency in high CO2 plants when compared to low CO2 plants. Several biochemical parameters, as the decrease in chlorophyll content and the increase in antioxidants indicate stress in plants exposed to a high CO2 environment.