Potential remediation of 137Cs and 90Sr contaminated soil by accumulation in Alamo switchgrass

Cesium-137 ( 137Cs) and Strontium-90 ( 90Sr) are radionuclides characteristic of nuclear fallout from nuclear weapons testing and nuclear reactor accidents. Alamo switchgrass (Panicum virginatum L.) is a perennial C4 species native to central North America that produces exceptionally high biomass yields in short periods of time. In three separate experiments, Alamo switchgrass plants were tested for their ability to accumulate 137 Cs and 90 Sr from a contaminated growth medium. Plants in experiment I were grown in 33 x 20 x 7 cm plastic pans containing 2.5 kg sand. Plants in experiments 2 and 3 were grown in 30 x 3 cm diameter test tubes containing 0.3 kg growth medium. After 3 months of plant growth, either 102 Bq 137 Cs or 73 Bq 90Sr g-1 soil were added to the growth medium. Plants in all three experiments were grown within a greenhouse that was maintained at 22 ± 2 °C with a photosynthetic active radiation of 400-700 umol m-2 s-1 and a 14-16 h photoperiod. Above-ground plant biomass did not differ between plants that were not exposed to these radionuclides (controls) and those that were exposed to growth medium containing 137Cs or 90Sr over the course of the experiment. Plants accumulated 44 and 36% of the total amount of 90Sr and 137CS added to growth medium after the first 5 harvests. After the first two harvests, the concentration of 137CS and 90Sr in plant tissue and the amount of 137Cs or 90Sr removed from growth medium declined with each successive harvest. Duration of exposure correlated curvilinearly with accumulation of both 90Sr and 137CS by plants (r2 = 0.95 and 0.78, respectively). As concentration of both 137Cs and 90Sr in growth medium increased, plant accumulation of both radionuclides increased and correlated curvilinearly in seedlings (r2 = 0.83 and 0.89 respectively)

Arbuscular mycorrhizal response to adverse soil conditions

Adverse conditions are a pervasive feature in both natural as well as agronomic soils. The soil environment is constantly changing with regard to moisture, temperature and nutrition. In addition, soil properties such as fertility, pH and aeration are often changed to improve crop yields. Soils have been unintentionally contaminated as a result of accidents that occur during agronomic operations or intentionally contaminated in mining or manufacturing operations by disposal of chemicals that are toxic to plants and micro-organisms. Mycorrhizal associations in terrestrial ecosystems influence organic and inorganic nutrient relationships, water relations and carbon cycling in plants. Relatively little is known about factors that control the vigour and extent of mycorrhization. This lack of understanding arises in large part from the difficulty of studying the intact association, which is a functionally and anatomically distinct structure comprising two biologically different organisms, e.g., plants and arbuscular mycorrhizae (AM) fungi. The formation and function of mycorrhizal relationships are affected by edaphic conditions such as soil composition, moisture, temperature, pH, cation exchange capacity. They are also affected by anthropogenic stressers such as heavy metals, pesticides and soil compaction. An organism's response to stress may involve interactions among various avoidance and tolerance mechanisms (Taylor, 1978; Tingey and Taylor, 1982; Tingey and Anderson, 1991). Stress avoidance mechanisms influence the amount and rate at which stress will reach the target site in the plant. Stress tolerance is defined as resistance via an ability "to come to thermodynamic equilibrium to the stress" without being killed (Levitt, 1980). In this chapter, we shall review the effects of a number of soil-associated stressers, including soil moisture, temperature, pH, heavy metals, agricultural practices and pesticides on AM development and function and host plant tolerance to these stresses. Several publications have reviewed the impact of various stresses on plant-mycorrhizal interactions (Anderson and Rygiewicz, 1991; Read, 1991; Van Duin et al, 1991; Sylvia and Williams, 1992), which provide additional information on this subject

Influence of adverse soil conditions on the formation and function of Arbuscular mycorrhizas

The majority of plants have mycorrhizal fungi associated with them. Mycorrhizal fungi are ecologically significant because they form relationships in and on the roots of a host plant in a symbiotic association. The host plant provides the fungus with soluble carbon sources, and the fungus provides the host plant with an increased capacity to absorb water and nutrients from the soil. Adverse conditions are a pervasive feature in both natural and agronomic soils. The soil environment is constantly changing with regard to moisture, temperature and nutrient availability. In addition, soil properties are often manipulated to improve crop yields. In many cases, soils may be contaminated through disposal of chemicals that are toxic to plants and microorganisms. The formation and function of mycorrhizal relationships are affected by edaphic conditions such as soil composition, moisture, temperature, pH, cation exchange capacity, and also by anthropogenic stressors including soil compaction, metals and pesticides. Arbuscular mycorrhizal fungi are of interest for their reported roles in alleviation of diverse soil-associated plant stressors, including those induced by metals and polychlorinated aliphatic and phenolic pollutants. Much mycorrhizal research has investigated the impact of extremes in water, temperature, pH and inorganic nutrient availability on mycorrhizal formation and nutrient acquisition. Evaluation of the efficacy of plant–mycorrhizal associations to remediate soils contaminated with toxic materials deserves increased attention. Before the full potential benefits of arbuscular mycorrhizal fungi to reclaim contaminated soils can be realized, research advances are needed to improve our understanding of the physiology of mycorrhizae subjected to adverse physical and chemical conditions. This paper will review literature and discuss the implications of soil contamination on formation and function of arbuscular mycorrhizal associations

A composite transcriptional signature differentiates responses towards closely related herbicides in Arabidopsis thaliana and Brassica napus

In this study, genome-wide expression profiling based on Affymetrix ATH1 arrays was used to identify discriminating responses of Arabidopsis thaliana to five herbicides, which contain active ingredients targeting two different branches of amino acid biosynthesis. One herbicide contained glyphosate, which targets 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), while the other four herbicides contain different acetolactate synthase (ALS) inhibiting compounds. In contrast to the herbicide containing glyphosate, which affected only a few transcripts, many effects of the ALS inhibiting herbicides were revealed based on transcriptional changes related to ribosome biogenesis and translation, secondary metabolism, cell wall modification and growth. The expression pattern of a set of 101 genes provided a specific, composite signature that was distinct from other major stress responses and differentiated among herbicides targeting the same enzyme (ALS) or containing the same chemical class of active ingredient (sulfonylurea). A set of homologous genes could be identified in Brassica napus that exhibited a similar expression pattern and correctly distinguished exposure to the five herbicides. Our results show the ability of a limited number of genes to classify and differentiate responses to closely related herbicides in A. thaliana and B. napus and the transferability of a complex transcriptional signature across species

Bt Crop Effects on Functional Guilds of Non-Target Arthropods: A Meta-Analysis

Background: Uncertainty persists over the environmental effects of genetically-engineered crops that produce the insecticidal Cry proteins of Bacillus thuringiensis (Bt). We performed meta-analyses on a modified public database to synthesize current knowledge about the effects of Bt cotton, maize and potato on the abundance and interactions of arthropod non-target functional guilds. Methodology/Principal Findings: We compared the abundance of predators, parasitoids, omnivores, detritivores and herbivores under scenarios in which neither, only the non-Bt crops, or both Bt and non-Bt crops received insecticide treatments. Predators were less abundant in Bt cotton compared to unsprayed non-Bt controls. As expected, fewer specialist parasitoids of the target pest occurred in Bt maize fields compared to unsprayed non-Bt controls, but no significant reduction was detected for other parasitoids. Numbers of predators and herbivores were higher in Bt crops compared to sprayed non-Bt controls, and type of insecticide influenced the magnitude of the difference. Omnivores and detritivores were more abundant in insecticide-treated controls and for the latter guild this was associated with reductions of their predators in sprayed non-Bt maize. No differences in abundance were found when both Bt and non-Bt crops were sprayed. Predator-to-prey ratios were unchanged by either Bt crops or the use of insecticides; ratios were higher in Bt maize relative to the sprayed non-Bt control

Wetland and riparian plant communities at risk of invasion by transgenic herbicide-resistant \u3ci\u3eAgrostis\u3c/i\u3e spp. in central Oregon

Creeping bentgrass (Agrostis stolonifera) and redtop (A. gigantea) are introduced turfgrasses that are naturalized throughout the northern U.S. Interest in creeping bentgrass has risen following the 2003 escape of a genetically modified (GM), herbicide- resistant cultivar near Madras, Oregon. The objectives of this study were to characterize the floristic attributes of the plant communities associated with naturalized Agrostis populations in the Madras area, and to identify plant communities at risk of invasion by transgenic Agrostis. Vegetation data collected from 62 stratified random vegetation plots with and without A. stolonifera and A. gigantea identified 11 distinct plant communities. Community composition was strongly correlated with an indirect soil moisture index based on the wetland status of individual species. Results indicate that wetland plant communities are at the highest risk of invasion by transgenic A. stolonifera. Also, inter-specific gene flow to A. gigantea could affect additional habitats and plant communities where A. stolonifera is not found. Both A. stolonifera and A. gigantea were invasive in wetland and riparian settings in the Madras study area, and introducing glyphosate (e.g., Roundup®, Rodeo®) herbicide tolerance into these populations would eliminate the primary means of control for these species

Influence of adverse soil conditions on the formation and function of Arbuscular mycorrhizas

The majority of plants have mycorrhizal fungi associated with them. Mycorrhizal fungi are ecologically significant because they form relationships in and on the roots of a host plant in a symbiotic association. The host plant provides the fungus with soluble carbon sources, and the fungus provides the host plant with an increased capacity to absorb water and nutrients from the soil. Adverse conditions are a pervasive feature in both natural and agronomic soils. The soil environment is constantly changing with regard to moisture, temperature and nutrient availability. In addition, soil properties are often manipulated to improve crop yields. In many cases, soils may be contaminated through disposal of chemicals that are toxic to plants and microorganisms. The formation and function of mycorrhizal relationships are affected by edaphic conditions such as soil composition, moisture, temperature, pH, cation exchange capacity, and also by anthropogenic stressors including soil compaction, metals and pesticides. Arbuscular mycorrhizal fungi are of interest for their reported roles in alleviation of diverse soil-associated plant stressors, including those induced by metals and polychlorinated aliphatic and phenolic pollutants. Much mycorrhizal research has investigated the impact of extremes in water, temperature, pH and inorganic nutrient availability on mycorrhizal formation and nutrient acquisition. Evaluation of the efficacy of plant–mycorrhizal associations to remediate soils contaminated with toxic materials deserves increased attention. Before the full potential benefits of arbuscular mycorrhizal fungi to reclaim contaminated soils can be realized, research advances are needed to improve our understanding of the physiology of mycorrhizae subjected to adverse physical and chemical conditions. This paper will review literature and discuss the implications of soil contamination on formation and function of arbuscular mycorrhizal associations

Arbuscular mycorrhizal response to adverse soil conditions

Adverse conditions are a pervasive feature in both natural as well as agronomic soils. The soil environment is constantly changing with regard to moisture, temperature and nutrition. In addition, soil properties such as fertility, pH and aeration are often changed to improve crop yields. Soils have been unintentionally contaminated as a result of accidents that occur during agronomic operations or intentionally contaminated in mining or manufacturing operations by disposal of chemicals that are toxic to plants and micro-organisms. Mycorrhizal associations in terrestrial ecosystems influence organic and inorganic nutrient relationships, water relations and carbon cycling in plants. Relatively little is known about factors that control the vigour and extent of mycorrhization. This lack of understanding arises in large part from the difficulty of studying the intact association, which is a functionally and anatomically distinct structure comprising two biologically different organisms, e.g., plants and arbuscular mycorrhizae (AM) fungi. The formation and function of mycorrhizal relationships are affected by edaphic conditions such as soil composition, moisture, temperature, pH, cation exchange capacity. They are also affected by anthropogenic stressers such as heavy metals, pesticides and soil compaction. An organism's response to stress may involve interactions among various avoidance and tolerance mechanisms (Taylor, 1978; Tingey and Taylor, 1982; Tingey and Anderson, 1991). Stress avoidance mechanisms influence the amount and rate at which stress will reach the target site in the plant. Stress tolerance is defined as resistance via an ability "to come to thermodynamic equilibrium to the stress" without being killed (Levitt, 1980). In this chapter, we shall review the effects of a number of soil-associated stressers, including soil moisture, temperature, pH, heavy metals, agricultural practices and pesticides on AM development and function and host plant tolerance to these stresses. Several publications have reviewed the impact of various stresses on plant-mycorrhizal interactions (Anderson and Rygiewicz, 1991; Read, 1991; Van Duin et al, 1991; Sylvia and Williams, 1992), which provide additional information on this subject