Hazardous doses of the herbicide imazamox in wild plant species and oilseed rape cultivars

Imidazolinones and crops resistant to these herbicides have successfully been introduced recently in some European countries. Imazamox has a high efficacy, moderate persistence and ecotoxicity, but data on hazardous doses (HD) in non-target plants and species sensitivity distributions (SSDs) are still scarce. To screen a larger variety of plant taxa in standardized vegetative vigor tests, 22 wild plant species and 14 oilseed rape (OSR) cultivars were sown into trays filled with a standard soil. When seedlings had reached the three-to-four leaf stage, plants were exposed to a single application of the herbicide Bolero® using a commercial pump sprayer. The five treatments corresponded to rates of 0 (control), 0.4, 4, 20 and 40 g/ha of imazamox with latter representing the recommended dose in Switzerland. Two weeks after the application, five plants per treatment were sub-sampled at random and visible injuries and fresh weights were recorded as endpoints for herbicidal effects. Dose-response curves and effective doses (EDs) were fitted using the drc package of the statistical software R and SSDs were obtained using ETX2.0. ED50 varied between 0.006 and 37 g/ha of the active ingredient in Nigella arvensis and Brassica rapa. Several dose-response curves indicated hormetic effects at a hundredth of the recommended field dose. In OSR, exposure to the field rate (40 g/ha) resulted in growth reductions between 28 and 97 % in the non imazamox-tolerant cultivars and in growth stimulations of up to 20 % in imazamox-tolerant cultivars. Responses were unrelated to leaf thickness, growth rates and the taxonomy of the tested species. Hazardous doses were 0.32 g/ha for HD5 and 3.9 g/ha for HD50 indicating that 50 % of the non-target plants would be affected at a tenth of the recommended dose. Based on general herbicide drift values the results suggest that potentially adverse effects may be expected up to a distance of 4 m offsite. Keywords: Clearfield, non-target plants, plant growth tests, plant functional typesSchädliche Dosen des Herbizids Imazamox bei verschiedenen Wildpflanzenarten und RapssortenImidazolinone und gegen diese Herbizide resistente Sorten einiger Kulturarten wurden in den letzten Jahren in einigen Europäischen Ländern erfolgreich eingeführt. Imazamox hat eine hohe Wirksamkeit, moderate Persistenz und Ökotoxizität, aber es gibt bislang nur wenige Informationen zu Schaddosen (hazardous doses, HD) in Nichtzielpflanzen und Art-Sensitivitäts-Spektren (species sensitivity distributions, SSDs). Um eine größere Anzahl von Pflanzenarten in standardisierten Wachstumstests zu überprüfen, wurden 22 Wildpflanzenarten und 14 Rapssorten in mit Standardboden gefüllten Schalen ausgesät. Bei Erreichung des Drei- bis Vierblattstadiums wurden die Pflanzen einmal mittels Pumpsprüher mit dem Herbizid Bolero® behandelt. Die fünf eingesetzten Behandlungen entsprachen den Dosen 0 (Kontrolle), 0.4, 4, 20 und 40 g AS/ha, wobei die letztere in der Schweiz die empfohlene Aufwandmenge darstellte. Zwei Wochen nach der Applikation wurden fünf Pflanzen pro Behandlung nach dem Zufallsprinzip geerntet, wobei sichtbare Schäden und Frischgewichte als Wirkkriterien betrachtet wurden. Dosis-Wirkungs-Kurven und effektive Dosen (EDs) wurden mit Hilfe des drc-Pakets mit der Statistik-Software R berechnet und SSDs wurden mittels ETX2.0 abgeleitet. Die ED50-Werte schwankten zwischen 0.006 und 37 g/ha der aktiven Substanz in Nigella arvensis und Brassica rapa. Viele der Dosis-Wirkungs-Beziehungen deuteten hormetische Effekte bei einem Hundertstel der empfohlenen Aufwandmenge an. Bei den nicht Imazamox-toleranten Rapssorten wurden bei der empfohlenen Aufwandmenge (40 g/ha) Wachstumsreduktionen zwischen 28 und 97 % beobachtet, während in den Imazamox-toleranten Sorten Wachstumsstimulationen von bis zu 20 % auftraten. Die beobachteten Effekte standen in keinem Zusammenhang mit der Blattdichte, den Wachstumsraten und der Taxonomie der überprüften Pflanzenarten. Die ermittelten Schaddosen betrugen 0.32 g/ha für HD5 und 3.9 g/ha für HD50, was darauf hindeutet, dass 50 % der Nichtzielarten bei einem Zehntel der empfohlenen Aufwandmenge beeinträchtigt würden. Wenn man die Abdrifteckwerte für Herbizidanwendungen zu Grunde legt, wären potenziell nachteilige Effekte bis zu einer Entfernung von 4 m zum Feldrand zu erwarten. Stichwörter: Clearfield, funktionelle Pflanzentypen, Nichtzielpflanzen, Pflanzenwachstumstest

Tree-rings analysis to reconstruct atmospheric mercury contamination at a historical mining site

Mercury (Hg) is a global environmental concern due to its toxicity (especially high in methylated form) and the long-range distribution of its gaseous elemental form (GEM). Hg-contaminated areas, such as abandoned mining sites, pose intrinsic difficulties for their management and heavy monitoring costs. In these environments, plant-based solutions may play a key role in the ecosystem quality assessment and support remediation strategies, combining reliability and costeffectiveness. In this study, we adopted a biomonitoring approach by using tree rings of four different species collected in the proximity of the miningmetallurgical area of Abbadia San Salvatore, central Italy, a major former Hg mining district whose reclamation is currently in progress. Our dendrochemical analysis was aimed at identifying the historical changes of local atmospheric Hg contamination and at singling out, for the first time in the study area, other potentially toxic elements (PTEs) associated with the past mining activity. Collected cores dated back to early as 1940 and provided the temporal patterns of atmospheric Hg emission vs the produced liquid quantities, so reconstructing the historical impact of the mining site on nearby terrestrial ecosystems and resident human population. Current GEM contamination was found about twenty times lower than that of the fully operational mine periods. From a first survey on other PTEs, thallium (Tl) and lead (Pb) appeared to be potentially associated with the mining activity, thus suggesting new working assumptions for further dendrochemical analyses and for the inclusion of Pb in human biomonitoring surveys of the Mt. Amiata area, actually not present in the control list. The results prompt a more thorough assessment by tracking for a longer time span a critical site that is an ideal open-field lab to study the ecophysiology of different tree species in relation to environmental behavior of PTEs for better-assessing wildlife and human exposures

Investigations on plant functional traits, epidermal structures and the ecophysiology of the novel bioenergy species Sida hermaphrodita Rusby and Silphium perfoliatum L.

A growth experiment was performed with different accessions of the novel bioenergy species Sida hermaphrodita Rusby (Fanpetals, Malvaceae) and Silphium perfoliatum L. (Cup Plant, Asteraceae) to study differences between the perennial shrubs and the variation among biotypes. Non-destructive assessments (phenology, leaf numbers, height, SPAD and gas exchange) and several harvests were conducted to examine growth, allometry and the quality of shoot material (C:N, raw ash, protein, fibre, fat, calorific value and leafδ13C). In addition to the functional analyses, epidermal structures of two widely used accessions were addressed to give insight into anatomical properties of the species.   In the establishment phase, productivity was higher on average in S. hermaphrodita than in S. perfoliatum since latter remains in the rosette stage in the first year. While the accessions of S. hermaphrodita did not significantly differ in growth, functional traits and forage quality, S. perfoliatum showed large biotypic variation. Leaf water and ash contents, raw protein and fat levels were higher in latter species, while raw fibre contentswere twice as highin S. hermaphrodita. At the end of the season, the calorific value of senesced stems of S. hermaphrodita proved to be higher than that of senesced leaves of S. perfoliatum pointing to its suitability of as a solid fuel.   Despite the shorter longevity, lower SPAD and smaller size, the delicate leaves of S. hermaphrodita had more stomata, higher photosynthetic rates and higher stomatal conductances than the robust leaves of S. perfoliatum. Less negative δ13C signatures in S. perfoliatum (-27.3 ‰) compared to S. hermaphrodita (-30.24 ‰), point to the potentially higher water use efficiency of S. perfoliatum. Further investigations on the relationships between leaf properties, carbon acquisition and stomatal conductance under dry conditions may serve to select productive lines of the bioenergy species on marginal land thus avoiding conflicts with the farming of food crops

Discharge and Water Quality of the River Moselle from 1990 to 2020 as Related to Climatic Changes and De-Industrialization

Reductions in industrial pollutant loads and the introduction and modernization of wastewater treatment facilities have improved the quality of inland waters in Europe and elsewhere, but climatic change, changes in runoff and the legacy of mine wastes may increase pressures on many aquatic environments. In the present study, data obtained by monitoring the French–German river are collated to visualize long-term trends in the pollution, river discharges and temperatures of Moselle waters. While air temperatures and accumulated heat sums in the catchment area showed an upward trend, precipitation and discharge levels as well as river temperatures were less affected by the ongoing climatic change. At the same time, the electric conductivity, i.e., the total suspended solids, did not show the anticipated reductions, while oxygen levels and pH values have showed upward trends since the 1990s. Despite the improvements in classical water quality parameters, the flooding of abandoned mines, increased water abstraction for cooling and agriculture and untreated old and emerging pollutants may aggravate environmental problems in the future. Climatic change will probably modify the runoff of pollutant loads by increasing the severity of flash floods and by concentrating water pollutants in drought spells

Air quality in post-mining towns: tracking potentially toxic elements using tree leaves

In this study, leaves of the evergreen holm oak Quercus ilex were used to assess airborne contamination of potentially toxic elements (PTEs) at five towns located on the slopes of the Mt. Amiata (central Italy), an area with a long history of mining and, more recently, an important district for the industrial exploitation of geothermal energy. PTE composition and covariance of washed and unwashed Q. ilex leaves of three different ages (6, 12 and 24 month-old) were used to identify atmospheric inputs of PTEs at residential areas, evaluate long-term adsorption and retention of PTEs by the leaves, thus providing an indication of potential human exposure. Moreover, the determination of foliar concentrations of major elements (C, N, S and P) allowed an assessment of the nutritional status of the investigated urban tree stands which excluded the existence of stress condition caused by air pollution or other disturbances. Results indicated that overall Pb, Cu, and Cd concentration were low in the investigated urban sites, if compared with similar studies conducted in larger Italian cities, denoting a low contribution of vehicular traffic to the atmospheric pathway. The five urban settlements were characterized by a specific profile of elements (Al, Ba, Hg and Sb) enriched in unwashed leaves, resulting from the distinct geochemical characteristics of the area and from diffuse (i.e., urban activity) and point sources of PTEs emission (i.e., brownfields, geothermal power plants). The latter sources primarily govern the distribution of Hg, whose contamination was found to be very localized close to a major abandoned mining area. Our data provided quantitative evidence of the spectrum of PTEs potentially impacting resident population and may prove useful in support of follow-up instrumental monitoring campaigns of air quality, as well as for human health and ecological risk assessments

Divergent N Deficiency-Dependent Senescence and Transcriptome Response in Developmentally Old and Young Brassica napus Leaves

In the spring oilseed rape (OSR) cultivar ‘Mozart’ grown under optimal N supply (NO) or mild N deficiency (NL) the transcriptome changes associated with progressing age until early senescence in developmentally old lower canopy leaves (leaf #4) and younger higher canopy leaves (leaf #8) were investigated. Twelve weeks old NO and NL plants appeared phenotypically and transcriptomically identical, but thereafter distinct nutrition-dependent differences in gene expression patterns in lower and upper canopy leaves emerged. In NO leaves #4 of 14-week-old compared to 13-week-old plants, ∼600 genes were up- or downregulated, whereas in NL leaves #4 ∼3000 genes were up- or downregulated. In contrast, in 15-week-old compared to 13-week-old upper canopy leaves #8 more genes were up- or downregulated in optimally N-supplied plants (∼2000 genes) than in N-depleted plants (∼750 genes). This opposing effect of N depletion on gene regulation was even more prominent among photosynthesis-related genes (PSGs). Between week 13 and 14 in leaves #4, 99 of 110 PSGs were downregulated in NL plants, but none in NO plants. In contrast, from weeks 13 to 16 in leaves #8 of NL plants only 11 PSGs were downregulated in comparison to 66 PSGs in NO plants. Different effects of N depletion in lower versus upper canopy leaves were also apparent in upregulation of autophagy genes and NAC transcription factors. More than half of the regulated NAC and WRKY transcription factor, autophagy and protease genes were specifically regulated in NL leaves #4 or NO leaves #8 and thus may contribute to differences in senescence and nutrient mobilization in these leaves. We suggest that in N-deficient plants the upper leaves retain their N resources longer than in amply fertilized plants and remobilize them only after shedding of the lower leaves

Differential elemental stoichiometry of two Mediterranean evergreen woody plants over a geochemically heterogeneous area

Leaf nutrient composition and stoichiometry reflect complex interactions of the plant with its environment and are useful traits to explore ecological processes and relationships. In the present study, the foliar elemental compositions of two common Mediterranean woody species, the evergreen broad-leaved Quercus ilex and the coniferous Pinus pinaster growing in an area of Central Italy known for geochemical and geothermal anomalies, were investigated. To assess the site-specific and age-dependent pattern of foliar composition and stoichiometry, macronutrients (C, N, P, K, Mg, S) and trace elements (Al, As, Ba, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Sb, V, Zn) were determined in leaves and needles of three different ages (6-, 12- and 24-month-old) collected from metalliferous (geothermal, mining) and rural areas. Leaves of Q. ilex showed comparatively high concentrations of micronutrients (i.e., Cu, Fe and Zn), while needles of P. pinaster accumulated significantly high concentrations of potentially toxic elements (i.e., As, Pb and S). No significant trend was found in elemental concentrations in relation to the age of leaves and needles. Multi-element stoichiometry of P. pinaster was driven by the geochemical heterogeneity of the sites, suggesting plastic adaptation at the sites with the most selective edaphoclimatic conditions (i.e., patches with nutrient poor and metalliferous soils). On the other hand, the content of both nutrients and potentially toxic elements in Q. ilex leaves varied little across the study area, reflecting stoichiometric stability; this is consistent with the ecophysiological features of Q. ilex as a late-successional species with a dominant role in the ecosystems of the Mediterranean area. Our findings demonstrate the value of foliar stoichiometric traits for understanding plant adaptation in a heterogeneous environment and also the consequences of biotic interactions during succession

Nitrogen Supply Drives Senescence-Related Seed Storage Protein Expression in Rapeseed Leaves

In general, yield and fruit quality strongly rely on efficient nutrient remobilization during plant development and senescence. Transcriptome changes associated with senescence in spring oilseed rape grown under optimal nitrogen supply or mild nitrogen deficiency revealed differences in senescence and nutrient mobilization in old lower canopy leaves and younger higher canopy leaves [1]. Having a closer look at this transcriptome analyses, we identified the major classes of seed storage proteins (SSP) to be expressed in vegetative tissue, namely leaf and stem tissue. Expression of SSPs was not only dependent on the nitrogen supply but transcripts appeared to correlate with intracellular H2O2 contents, which functions as well-known signaling molecule in developmental senescence. The abundance of SSPs in leaf material transiently progressed from the oldest leaves to the youngest. Moreover, stems also exhibited short-term production of SSPs, which hints at an interim storage function. In order to decipher whether hydrogen peroxide also functions as a signaling molecule in nitrogen deficiency-induced senescence, we analyzed hydrogen peroxide contents after complete nitrogen depletion in oilseed rape and Arabidopsis plants. In both cases, hydrogen peroxide contents were lower in nitrogen deficient plants, indicating that at least parts of the developmental senescence program appear to be suppressed under nitrogen deficiency

Linking N2O concentrations in different soil depths to denitrification genes abundances under the influence of an elevated atmospheric CO2 concentration

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Linking N2O concentrations in different soil depths to denitrification genes abundances under the influence of an elevated atmospheric CO2 concentration

The production of nitrous oxide (N2O) from agricultural soils by denitrification forms a major part of the global emission of this important greenhouse gas. Due to a lack of the nosZ gene encoding the nitrous oxide reductase, some denitrifying bacteria are not able to reduce N2O to N2. Until now, factors influencing the proportion of denitrifying bacteria having this truncated pathway are not well understood. Under a changing climate, namely increasing concentrations of CO2 in the atmosphere, plant growth and exudation as well as soil moisture will be influenced which probably also affects conditions for denitrifying bacteria in soil. We investigated in the present study N2O production rates as well as densities of functional genes (narG, napA, nirK, nirS and nosZ) encoding reductases involved in the denitrification process in different soil depths of an oilseed rape field under both, ambient and elevated CO2 concentrations (Mini-FACE Experiment) during the growing season 2007. Gas samples were collected in soil air sampling probes installed at three different soil depths (5, 15 and 30 cm). Soil samples were collected at three depths (0-10, 10-20 and 20-30 cm) on sixdates during the season 2007. Soil temperature, precipitation and soil moisture content were monitored in the field. N2O concentrations in soil were highest in deeper soil layers under moist and high nitrate conditions. Total amounts of DNA as well as functional gene densities of denitrifying bacteria changed during the vegetation period with lower values when soil was dry. Effects of soil depth dominated over those of elevated atmospheric CO2 concentrations. However, during some periods throughout oilseed rape growth altered ratios of nosZ to napA indicate temporal changes in the soil bacterial denitrifier community