Mycorrhizal populations and fine root development on Norway spruce exposed to controlled doses of gaseous pollutants and simulated acidic rain treatments

Effects after long-term fumigation and simulated acidic rain (pH 4.0) treatment in open-top chambers (OTC) during 5 vegetation periods on ectomycorrhizal (EM) frequency, fine root structure and distribution of short roots were recorded for Norway spruce. Simultaneous application of ozone and SO(2) resulted in a significant decrease (P< or =0.01) in the proportion of EM root tips and an increase in the numbers of necrotic short roots. The observed differences were partly due to more than additive effects of ozone and SO(2). On the basis of EM and non-mycorrhizal (NM) short roots in the irrigated controls (OTC-V, pH 5.6, Ah-horizon: EM + NM/cm=0.05) the acid treatments resulted in drastic effects (P< or =0.05) on the branching density and the proportion of EM root tips and NM short roots. Relative numbers of short roots infected by indigenous EM fungi with trees in the fumigation treatments at pH 4.0 were similar: 1.5-1.9 EM tips/cm and differed noticeably from the control: 5.2 EM tips/cm. Again, increasing numbers of necrotic and NM short roots were noted. Parallel measurements by the ingrowth-core technique confirm the argument, that EM formation seems to be a reliable indicator of pollution-induced stress.     

Effects of mycorrhizae and other soil microbes on revegetation of heavy metal contaminated mine spoil

The effects of mycorrhizal fungi and other soil microorganisms on growth of two grasses, Andropogon gerardii Vitm. and Festuca arundinacea Schreb., in heavy metal-contaminated soil and mine tailings were investigated. A. gerardii is highly dependent on mycorrhizal fungi in native prairie, while F. arundinacea is a facultative mycotroph and relies on mycorrhizal symbiosis only in extremely infertile soils. Regardless of microbial amendments, neither plant species was able to establish and grow in the mine tailings. Both plant species grew in the moderately contaminated or non-contaminated soils, although A. gerardii grew in these soils only when mycorrhizal. Other soil microbes significantly improved growth of A. gerardii only in uncontaminated soil, but to a lesser extent than mycorrhizae. Although F. arundinacea was more highly colonized by mycorrhizal fungi than A. gerardii, neither microbial amendment affected growth of fescue in any soil. In several treatments mycorrhizal fungi adapted to uncontaminated soil stimulated plant growth more than mycorrhizae adapted to the moderately contaminated soil. However, mycorrhizal fungi adapted to contaminated soil did not increase the productivity of plant growth in contaminated soil more than fungi adapted to uncontaminated soil. A. gerardii plants inoculated with mycorrhizal fungi retained more Zn in roots than in shoots, confirming earlier reports that mycorrhizal fungi alter the translocation pattern of heavy metals in host plants. In contrast, mycorrhizae did not affect translocation patterns in F. arundinaceae, suggesting that the mycorrhizal dependence of a plant species is correlated with the retention of metals in roots. The correlation between mycorrhizal dependence of a plant species and mycorrhizal alteration of translocation pattern may also explain the inconsistent reports of mycorrhizal effects on translocation of heavy metals in plants. Plant response to mycorrhizal symbiosis may therefore provide a useful criterion for the selection of the plant species to be used in revegetation of contaminated sites.     

A modified glass bead compartment cultivation system for studies on nutrient and trace metal uptake by arbuscular mycorrhiza

A modified glass bead compartment cultivation system is described in which glass beads continue to be used in the hyphal compartment but are replaced by coarse river sand in the compartments for host plant roots and mycorrhizal hyphae. Arbuscular mycorrhizal (AM) associations were established using two host plant species, maize (Zea mays L.) and red clover (Trifolium pratense L.) and two AM fungi, Glomus mosseae and G. versiforme. When the standard and modified cultivation systems were compared, the new method yielded much more fungal tissue in the hyphal compartment. Using G. versiforme as the fungal symbiont, up to 30 mg of fungal dry matter (DM) was recovered from the hyphal compartment of mycorrhizal maize and about 6 mg from red clover. Multi-element analysis was conducted on samples of host plant roots and shoots and on harvested fungal biomass. Concentrations of P, Cu and Zn were much higher in the fungal biomass than in the roots or shoots of the host plants but fungal concentrations of K, Ca, Mg, Fe and Mn were similar to or lower than those in the plants. There were also significant differences in nutrient concentrations between the two AM fungi and these may be related to differences in their proportions of extraradical mycelium to spores. The high affinity of the fungal mycelium for Zn was very striking and is discussed in relation to the potential use of arbuscular mycorrhiza in the phytoremediation of Zn-polluted soils.     

Effects of arbuscular mycorrhizal fungi on the root uptake and translocation of radiocaesium

Because mycorrhizal fungi are intimately associated with plant roots, their importance in radionuclide (RN) recycling and subsequent dispersion into the biosphere has received an increasing interest. Recently, the capacity of arbuscular mycorrhizal fungi to take up and translocate radiocaesium to their host was demonstrated. However, the relative contribution of these processes in comparison to the ones of roots remains unknown. Here, the respective contributions of the hyphae of a Glomus species and the transformed carrot (Daucus carota L.) roots on radiocaesium uptake and translocation were compared and quantified. We observed that radiocaesium uptake by hyphae was significantly lower as compared to that of the roots, while the opposite was noted for radiocaesium translocation/uptake ratio. We also observed that the intraradical fungal structures might induce a local accumulation of radiocaesium and concurrently reduce its translocation within mycorrhizal roots. We believe that intraradical fungal structures might induce the down-regulation of radiocaesium channels involved in the transport processes of radiocaesium towards the xylem.     

Stress interactions and mycorrhizal plant response: understanding carbon allocation priorities

In this paper, a framework is presented for studying responses of mycorrhiza to external stresses, including possible feedback effects which are likely to occur. The authors review recent literature linking carbon allocation and host/fungal response under natural and anthropogenic stress, and present a conceptual model to discuss how carbon may be involved in singular and multiple stress interactions of mycorrhizal seedlings. Due to an integral integral role in metabollic processes, characterizing carbon allocation in controlled laboratory environments could be useful for understanding host/fungal responses to a variety of natural and anthropogenic stresses. Carbon allocation at the whole-plant level reflects an integrated response which links photosynthesis to growth and maintenance processes. A root-mycocosm system is described which permits spatial separation of a portion of extramatrical hyphae growing in association with seedling roots. Using this system, it is shown that root/hyphal respiratory release of pulse-labeled 14C follows a sigmoidal pattern, with typical lag, exponential and saturation phases. Total respiratory release of 14C per mg root and the fraction respired of total 14C allocated to the root is greater in ponderosa pine inoculated with Hebeloma crustuliniforme than in noninoculated controls. Results illustrate the nature of information than can be obtained using this system. Current projects using the mycocosms include characterizing the dynamics of carbon allocation under ozone stress, and following the fate of organic pollutants. The authors believe that the system could be used to differentiate fungal- and host-mediated responses to a large number of other stresses and to study a variety of physiological processes in mycorrhizal plants.     

Diversity of arbuscular mycorrhizal fungi in grassland spontaneously developed on area polluted by a fertilizer plant

Mycorrhizal colonization and diversity of arbuscular mycorrhizal fungi (AMF) were analyzed in a calcareous grassland with residual phosphate contamination 10 years after the closure of a pollutant fertilizer plant in Thuringia (Germany). AMF were detected in 21 of 22 plant species analyzed. Mean mycorrhization levels reached up to 74.5% root length colonized. AMF diversity was analyzed based on 104 sequences of the internal transcribed spacer (ITS) of the ribosomal DNA. Phylogenetic analyses revealed a total of 6 species all belonging to the genus Glomus. There was no overlap between species detected as active mycorrhizas on roots (2 taxa) or as spores (4 taxa). Compared to the regional context, the diversity of AMF at our field site was reduced, which may reflect a residual disturbance effect. However, none of the detected species was exclusive to the polluted site as they are commonly found in the region.     

Mycorrhizal mediation of plant response to atmospheric change: Air quality concepts and research considerations

The term 'global climate change' encompasses many physical and chemical changes in the atmosphere that have been induced by anthropogenic pollutants. Increases in concentrations of CO2 and CH4 enhance the 'greenhouse effect' of the atmosphere and may contribute to changes in temperature and precipitation patterns at the earth's surface. Nitrogen oxides and SO2 are phytotoxic and also react with other pollutants to produce other phytotoxins in the troposphere such as O3 and acidic substances. However, release of chlorofluorocarbons into the atmosphere may cause depletion of stratospheric O3, increasing the transmittance of ultraviolet-B (UV-B) radiation to the earth's surface. Increased intensities of UV-B could affect plants and enhance photochemical reactions that generate some phytotoxic pollutants. The role of mycorrhizae in plant responses to such stresses has received little attention. Although plans for several research programs have acknowledged the importance of drought tolerance and soil fertility in plant responses to atmospheric stresses, mycorrhizae are rarely targeted to receive specific investigation. Most vascular land plants form mycorrhizae, so the role of mycorrhizae in mediating plant responses to atmospheric change may be an important consideration in predicting effects of atmospheric changes on plants in managed and natural ecosystems.     

Prediction of phenanthrene uptake by plants with a partition-limited model

The performance of a partition-limited model on prediction of phenanthrene uptake by a wide variety of plant species was evaluated using a greenhouse study. The model predictions of root or shoot concentrations for tested plant species were all within an order of magnitude of the observed values. Modeled root concentrations appeared to be more accurate than modeled shoot concentrations. The differences of simulated and experimented concentrations of phenanthrene in roots and shoots of three representative plant species, including ryegrass, flowering Chinese cabbage, and three-colored amaranth, were less than 81% for roots and 103% for shoots. Results are promising in that the alpha(pt) values of the partition-limited model for root uptake of phenanthrene correlate well with root lipid contents. Additionally, a significantly positive correlation is also observed between root concentration factors (RCFs, defined as the ratio of contaminant concentrations in root and in soil on a dry weight basis) of phenanthrene and root lipid contents. Results from this study suggest that the partition-limited model may have potential applications for predicting the plant PAH concentration in contaminated sites.     

Responses to projected changes in climate and UV-B at the species level

Environmental manipulation experiments showed that species respond individualistically to each environmental-change variable. The greatest responses of plants were generally to nutrient, particularly nitrogen, addition. Summer warming experiments showed that woody plant responses were dominant and that mosses and lichens became less abundant. Responses to warming were controlled by moisture availability and snow cover. Many invertebrates increased population growth in response to summer warming, as long as desiccation was not induced. CO2 and UV-B enrichment experiments showed that plant and animal responses were small. However, some microorganisms and species of fungi were sensitive to increased UV-B and some intensive mutagenic actions could, perhaps, lead to unexpected epidemic outbreaks. Tundra soil heating, CO2 enrichment and amendment with mineral nutrients generally accelerated microbial activity. Algae are likely to dominate cyanobacteria in milder climates. Expected increases in winter freeze-thaw cycles leading to ice-crust formation are likely to severely reduce winter survival rate and disrupt the population dynamics of many terrestrial animals. A deeper snow cover is likely to restrict access to winter pastures by reindeer/caribou and their ability to flee from predators while any earlier onset of the snow-free period is likely to stimulate increased plant growth. Initial species responses to climate change might occur at the sub-species level: an Arctic plant or animal species with high genetic/racial diversity has proved an ability to adapt to different environmental conditions in the past and is likely to do so also in the future. Indigenous knowledge, air photographs, satellite images and monitoring show that changes in the distributions of some species are already occurring: Arctic vegetation is becoming more shrubby and more productive, there have been recent changes in the ranges of caribou, and "new" species of insects and birds previously associated with areas south of the treeline have been recorded. In contrast, almost all Arctic breeding bird species are declining and models predict further quite dramatic reductions of the populations of tundra birds due to warming. Species-climate response surface models predict potential future ranges of current Arctic species that are often markedly reduced and displaced northwards in response to warming. In contrast, invertebrates and microorganisms are very likely to quickly expand their ranges northwards into the Arctic.     

Behavior of Trifolium repens and Lolium perenne growing in a heavy metal contaminated field: Plant metal concentration and phytotoxicity

The use of a vegetation cover for the management of heavy metal contaminated soils needs prior investigations on the plant species the best sustainable. In this work, behaviors of Trifolium repens and Lolium perenne, growing in a metal-polluted field located near a closed lead smelter, were investigated through Cd, Pb and Zn-plant metal concentrations and their phytotoxicity. In these plant species, metals were preferentially accumulated in roots than in shoots, as follow: Cd>Zn>Pb. Plant exposure to such metals induced oxidative stress in the considered organs as revealed by the variations in malondialdehyde levels and superoxide dismutase activities. These oxidative changes were closely related to metal levels, plant species and organs. Accordingly, L. perenne seemed to be more affected by metal-induced oxidative stress than T. repens. Taken together, these findings allow us to conclude that both the plant species could be suitable for the phytomanagement of metal-polluted soils.     

Reclamation of a bare industrial area contaminated by non-ferrous metals: physico-chemical and biological evaluation of the durability of soil treatment and revegetation

In 1990, 3 ha of a highly metal polluted acid sandy soil at the site of a former pyrometallurgical zinc smelter was treated with a combination of beringite and compost; beringite is a substance that has a strong metal immobilization capacity. After soil treatment and sowing of a mixture of metal-tolerant Agrostis capillaris and Festuca rubra, a healthy vegetation cover developed. Five years later, an evaluation was made of soil physico-chemical parameters, potential phytotoxicity, floristic and fungal diversity and mycorrhizal infection of the plant community. Phytotoxicity was shown to be maintained at the low level observed immediately after soil treatment. The water-extractable metal fraction of the treated soil was up to 70 times lower compared to the non-treated soil. The vegetation was still healthy and regenerating by vegetative means and by seed. Diversity of higher plant species and saprophytic fungi was extremely low in the untreated area due to the high soil toxicity and the absence of metal tolerant ecotypes of plants and fungi. On the treated soil, in contrast, the species richness of higher plants was much higher; several perennial forbs which are not noted as metal tolerant had colonized the revegetated area. Most of these species belong to mycotrophic families so that the presence of a mycorrhizal network in the soil promotes their establishment. The ubiquity of the mycorrhizal fungi in the roots showed that a functioning ecosystem was establishing. In non-treated soil, the mycorrhizal infection rates of the roots were consistently lower during the whole growing season.     

Arbuscular mycorrhiza enhanced arsenic resistance of both white clover (Trifolium repens Linn.) and ryegrass (Lolium perenne L.) plants in an arsenic-contaminated soil

In a compartmented cultivation system, white clover (Trifolium repens Linn.) and ryegrass (Lolium perenne L.), with their roots freely intermingled, or separated by 37 microm nylon mesh or plastic board, were grown together in an arsenic (As) contaminated soil. The influence of AM inoculation on plant growth, As uptake, phosphorus (P) nutrition, and plant competitions were investigated. Results showed that both plant species highly depended on mycorrhizas for surviving the As contamination. Mycorrhizal inoculation substantially improved plant P nutrition, and in contrast markedly decreased root to shoot As translocation and shoot As concentrations. It also showed that mycorrhizas affected the competition between the two co-existing plant species, preferentially benefiting the clover plants in term of nutrient acquisition and biomass production. Based on the present study, the role of AM fungi in plant adaptation to As contamination, and their potential use for ecological restoration of As contaminated soils are discussed.     

Nitrogen fertility and abiotic stresses management in cotton crop: a review

This review outlines nitrogen (N) responses in crop production and potential management decisions to ameliorate abiotic stresses for better crop production. N is a primary constituent of the nucleotides and proteins that are essential for life. Production and application of N fertilizers consume huge amounts of energy, and excess is detrimental to the environment. Therefore, increasing plant N use efficiency (NUE) is important for the development of sustainable agriculture. NUE has a key role in crop yield and can be enhanced by controlling loss of fertilizers by application of humic acid and natural polymers (hydrogels), having high water-holding capacity which can improve plant performance under field conditions. Abiotic stresses such as waterlogging, drought, heat, and salinity are the major limitations for successful crop production. Therefore, integrated management approaches such as addition of aminoethoxyvinylglycine (AVG), the film antitranspirant (di-1-p-menthene and pinolene) nutrients, hydrogels, and phytohormones may provide novel approaches to improve plant tolerance against abiotic stress-induced damage. Moreover, for plant breeders and molecular biologists, it is a challenge to develop cotton cultivars that can tolerate plant abiotic stresses while having high potential NUE for the future.     

Pesticide effects on freshwater zooplankton: an ecological perspective

The effects of pesticides on zooplankton are reviewed and their ecological significance is discussed. Toxicity is shown to vary depending on animal species, genotype, life stage, and size at birth. Natural stresses such as food shortage, oxygen depletion and odors of potential predators can also affect toxicity. Populations in the growth phase are vulnerable to pesticides but have the potential to recover rapidly from the damage. Pesticides may affect the population dynamics by controlling individual survival and reproduction, and by altering the sex ratio. Furthermore, toxic chemicals may control predation risk by changing swimming behavior and body morphology, and this in turn influences the population dynamics. Many zooplankton display morphological and behavioral responses to predators when exposed to their odor-producing chemicals. However, pesticides induce a maladaptive response to predator odor, and this poses an ecological risk. The following patterns are recognized as effects of pesticides at the community and ecosystem levels: (1) induction of dominance by small species; (2) an increase of species richness and diversity; and (3) elongation of the food chain and reduction of energy transfer efficiency from primary producers to top predators.     

The effect of mycorrhiza on the growth and elemental composition of Ni-hyperaccumulating plant Berkheya coddii Roessler

The effect of arbuscular mycorrhizal fungi (AMF) on growth and element uptake by Ni-hyperaccumulating plant, Berkheya coddii, was studied. Plants were grown under laboratory conditions on ultramafic soil without or with the AM fungi of different origin. The AM colonization, especially with the indigenous strain, significantly enhanced plants growth and their survival. AMF affected also the elemental concentrations that were studied with Particle-induced X-ray emission (PIXE). AMF (i) increased K and Fe in shoots, Zn and Mn in roots, P and Ca both, in roots and shoots; (ii) decreased Mn in shoots, Co and Ni both, in shoots and roots. Due to higher biomass of mycorrhizal plants, total Ni content was up to 20 times higher in mycorrhizal plants compared to the non-mycorrhizal ones. The AMF enhancement of Ni uptake may therefore provide an improvement of a presently used technique of nickel phytomining.     

Advanced research tools for fungal diversity and its impact on forest ecosystem

Fungi are dominant ecological participants in the forest ecosystems, which play a major role in recycling organic matter and channeling nutrients across trophic levels. Fungal populations are shaped by plant communities and environmental parameters, and in turn, fungal communities also impact the forest ecosystem through intrinsic participation of different fungal guilds. Mycorrhizal fungi result in conservation and stability of forest ecosystem, while pathogenic fungi can bring change in forest ecosystem, by replacing the dominant plant species with new or exotic plant species. Saprotrophic fungi, being ecological regulators in the forest ecosystem, convert dead tree logs into reusable constituents and complete the ecological cycles of nitrogen and carbon. However, fungal communities have not been studied in-depth with respect to functional, spatiotemporal, or environmental parameters. Previously, fungal diversity and its role in shaping the forest ecosystem were studied by traditional and laborious cultural methods, which were unable to achieve real-time results and draw a conclusive picture of fungal communities. This review highlights the latest advances in biological methods such as next-generation sequencing and meta’omics for observing fungal diversity in the forest ecosystem, the role of different fungal groups in shaping forest ecosystem, forest productivity, and nutrient cycling at global scales.

     

Exposure of Brassica juncea (L) to arsenic species in hydroponic medium: comparative analysis in accumulation and biochemical and transcriptional alterations

Arsenic (As) contamination in the environment has attracted considerable attention worldwide. The objective of the present study was to see the comparative effect of As species As(III) and As(V) on accumulation, biochemical responses, and gene expression analysis in Brassica juncea var. Pusa Jaganath (PJn). Hydroponically grown 14-day-old seedlings of B. juncea were treated with different concentrations of As(III) and As(V). Accumulation of total As increased with increasing concentration of both As species and exposure time, mainly in roots. Reduction in seed germination, root–shoot length, chlorophyll, and protein content were observed with increasing concentration and exposure time of both As species, being more in As(III)-treated leaves. PJn variety showed that antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)) and stress-related parameters (cysteine, proline, and malondialdehyde (MDA)) were stimulated and allows plant to tolerate both As species. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis in leaves showed significant changes in protein profile with more stringent effect with As(III) stress. Semiquantitative RT-PCR analysis showed regulation in expression of phytochelatin synthase (PCS), metallothionine-2 (MT-2), glutathione reductase (GR), and glutathione synthetase (GS) genes under both As(III) and As(V) stresses. Results suggested that accumulation and inhibition on physiological parameters differ according to the As species, while molecular and biochemical parameters showed a combinatorial type of tolerance mechanism against As(III) and As(V) stresses.     

Influence of Lead on Atrazine Uptake by Rice (Oryza sativa L.) Seedlings from Nutrient Solution (7 pp)

Background Atrazine is a widely used herbicide, and its persistence in soil and water causes environmental concerns. In the past, plat uptake processes are mainly investigated for single contaminants. However, in many cases, contaminants co-exist in environmental matrix, such as soil, and plant uptake of one contaminant may be influenced by its co-existing ones.Methods The uptake of atrazine by rice seedlings (Oryza sativa L.) from nutrient solution through the roots was investigated in a solution culture, over an exposure period of 4 weeks. Atrazine accumulation in plant tissues was determined by gas chromatography, and lead was determined using atomic absorption spectrometry.Results and Discussion With different ratios of atrazine and Pb2+ concentrations in solution, the observed atrazine concentrations in shoots and roots varied significantly. In atrazine-Pb2+ mixture systems, the added Pb2+ either increased or decreased the concentrations or BCFs of atrazine in seedlings (relative to those without Pb2+), depending on the atrazine-Pb2+ ratio in nutrient solution. The enhanced atrazine uptake results presumably from atrazine-Pb2+ complex formation. The reduced atrazine uptake, which occurred mainly at high atrazine concentrations, is attributed to atrazine toxicity that inhibited seedling growth and transpiration. Conclusion The formation of atrazine-Pb2+ complex both in the solution and within plant tissues may affect the accumulation of both contaminants by rice plants.     

Effect of external iron and arsenic species on chelant-enhanced iron bioavailability and arsenic uptake in rice (Oryza sativa L.)

This study was conducted to investigate the effect of external iron status and arsenic species on chelant-enhanced iron bioavailability and arsenic uptake. Rice seedlings (Oryza sativa L.) were used as model plant, and were grown in artificially contaminated sandy soils irrigated with Murashige and Skoog (MS) culture solution. Arsenate uptake in roots and shoots of rice seedlings were affected significantly (p > 0.05) while dimethylarsinic acid (DMAA) was not by the additional iron and chelating ligand treatments. Regardless of iron concentrations in the soil solution, HIDS increased arsenic uptake for roots more than EDTA and EDDS. Chelating ligands and arsenic species also influenced iron uptake in rice roots. Irrespective of arsenic species, HIDS was found to be more effective in the increase of iron bioavailability and uptake in rice roots compared to other chelants. There was a significant positive correlation (r = 0.78, p < 0.05) between arsenate and iron concentrations in the roots of rice seedlings grown with or without additional iron indicating that arsenate inhibit iron uptake. In contrast, there was no correlation between iron and DMAA uptake in roots. Poor correlation between iron and arsenic in shoots indicated that iron uptake in shoots was neither affected by additional iron nor by arsenic species. Compared to the control, chelating ligands increased iron uptake in shoots of rice seedlings significantly (p < 0.05). Regardless of additional iron and arsenic species, iron uptake in rice shoots did not differed among EDTA, EDDS, and HIDS treatments.     

Possible impacts of changes in UV-B radiation on North American trees and forests

Approximately 35 species representing 14 tree genera have been evaluated for responses to UV-B radiation in North America. The best representation has been in the conifers where some 20 species representing three genera have been studied. Overall, about 1/3 of these have demonstrated some deleterious response to UV-B. However, most negative impacts have been observed under controlled environment conditions where sensitivity may be enhanced. Therefore, it seems unlikely that expected levels of ozone depletion will result in direct losses in productivity. However, the role that ambient or enhanced levels of UV-B may play in forest ecosystem processes is more difficult to access. One possible indirect response of forests to changes in UV-B radiation levels could be via alterations in plant secondary metabolites. Increases in phenolics and flavonoids that enhance epidermal UV-screening effectiveness may also influence leaf development, water relations or ecosystem processes such as plant-herbivore interactions or decomposition.