Ecophysiology of iron homeostasis in plants

In nature, iron (Fe) occurs in abundance and ranks fourth among all elements on Earth’s surface. Still, its availability to plants is reduced, once this element is in the form of hydrated oxides, which can limit plant productivity and biomass production. On the other hand, in high concentrations, this essential micronutrient for the plants can become a toxic agent, increasing the environmental contamination. Fe is necessary for the maintenance of essential processes like respiration and photosynthesis, participating in the electron transport chain and in the conversion between Fe²⁺ and Fe³⁺, being a key element for carbon dioxide (CO₂) fixation and, therefore, important for crop production of cultivated or natural species. The balance of Fe should be strictly controlled, because both its deficiency and its toxicity affect the physiological process of plants. In aerated soils Fe is present in the form of Fe³⁺, which is the oxidized form and is less available to plants, so these organisms have developed different strategies for absorption, transport and storage of Fe. Deficiency and excess of Fe correlate with local soil conditions and with the care adopted in plant nutrition during the phenological phases and/or in the course of its cultivation. In situations of excessive accumulation of Fe in tissues, an enhancement of hydroxyl radical generation (OH^?) occurs by Fenton reaction. Here, we review the nutritional, genetic and ecophysiological aspects of uptake, translocation and accumulation of Fe ions in plants growing under conditions of deficiency or toxicity of this metal.     

Common vole (Microtus arvalis) ecology and management: implications for risk assessment of plant protection products

Common voles (Microtus arvalis) are common small mammals in some European landscapes. They can be a major rodent pest in European agriculture and they are also a representative generic focal small herbivorous mammal species used in risk assessment for plant protection products. In this paper, common vole population dynamics, habitat and food preferences, pest potential and use of the common vole as a model small wild mammal species in the risk assessment process are reviewed. Common voles are a component of agroecosystems in many parts of Europe, inhabiting agricultural areas (secondary habitats) when the carrying capacity of primary grassland habitats is exceeded. Colonisation of secondary habitats occurs during multiannual outbreaks, when population sizes can exceed 1000 individuals ha^?1. In such cases, in‐crop common vole population control management has been practised to avoid significant crop damage. The species' status as a crop pest, high fecundity, resilience to disturbance and intermittent colonisation of crop habitats are important characteristics that should be reflected in risk assessment. Based on the information provided in the scientific literature, it seems justified to modify elements of the current risk assessment scheme for plant protection products, including the use of realistic food intake rates, reduced assessment factors or the use of alternativee focal rodent species in particular European regions. Some of these adjustments are already being applied in some EU member states. Therefore, it seems reasonable consistently to apply such pragmatic and realistic approaches in risk assessments for plant protection products across the EU. © 2013 Society of Chemical Industry     

Nutrient release from decomposing leaf litter of temperate deciduous forest trees along a gradient of increasing tree species diversity

In the litter of six deciduous tree species (Fagus sylvatica, Tilia spp., Fraxinus excelsior, Carpinus betulus, Acer pseudoplatanus and Acer platanoides) and in stand-specific litter mixtures, we compared mass loss and nutrient release across diversity levels along a gradient of decreasing proportion of Fagus in stands with similar environmental and physical soil conditions. The litterbag studies ran over 22 months. The decomposition rate constants (k) of the temperate forest species ranged from k = 0.5 for Fagus to k = 1.5-2 for all other tree species. In Fagus, k was closely negatively correlated with the thickness of the litter layer and positively correlated with soil pH and isopod abundance. k was significantly higher in the mixed species stands (except for Carpinus and Fraxinus) and was positively correlated with earthworm abundance. Over the whole incubation time, nutrient amount and release rates of N, P, K, Ca and Mg as well as C-related ratios showed significant differences between tree species but no consistent differences among the diversity levels. Initial C-related nutrient ratios of the leaf litter and abundance of mesofauna and macrofauna were correlated with the length of time lag before nutrient release. We conclude that the mere number of tree species is not the main driver of nutrient release and decomposition processes, but that key groups of the decomposer fauna as well as the characteristic traits of the individual tree species are decisive.     

Food choice and impact of food sources from farms on blood coagulation in rodenticide resistant Norway rats

Rodents are mostly controlled by using anticoagulant rodenticides to minimise adverse effects along the food production chain. Genetic resistance to anticoagulant compounds occurs in populations of Norway rats (Rattus norvergicus) and other rodents throughout the world. This can be problematic for control operations and put predators and scavengers at risk because resistant prey individuals carry high anticoagulant loads. Single nucleotide polymorphisms (SNPs) in the vitamin K reductase complex subunit 1 (VKORC1) gene that are associated with rodenticide resistance are related to several pleiotropic effects including increased vitamin K requirement. The uptake of dietary vitamin K available from food sources present on farms including corn silage and garden herbs may mitigate such effects. We tested the preference for food rich in vitamin K1/3 in Norway rats susceptible or resistant to bromadiolone due to the homozygous amino acid variant Tyr139Cys. We also studied the effect of vitamin K consumption from several food sources on blood clotting in bromadiolone resistant and susceptible Norway rats. There was no general preference of rats for food sources rich in vitamin K. Surprisingly, there was no effect of vitamin K uptake on blood clotting times. However, the consumption of 4 of 5 corn silages prevented the rise in blood clotting times that otherwise occurred in vitamin K deficient bromadiolone resistant rats. This seemed to be due to substances with vitamin K activity present in silage and may contribute to the sustaining and spreading SNPs that are related to rodenticide resistance. As corn silage is becoming increasingly available to rats due to the expansion in generating bio-energy from corn silage, there may be a future increase in the occurrence of anticoagulant resistant Norway rats and associated problems in agro-ecosystems.     

A climatic risk analysis of the threat posed by the South American leaf blight (SALB) pathogen <Emphasis Type="Italic">Microcyclus ulei</Emphasis> to major rubber producing countries

In 2010, symptoms of cobweb disease were observed on cultivated Pleurotus eryngii crops in Spain. Based on morphological and genetic analyses, the causal agent of cobweb was identified as Cladobotryum mycophilum. Pathogenicity tests on fruit bodies were performed using conidial suspensions of three C. mycophilum isolates. The causal agent was re-isolated in 80–85 % of the fruit bodies inoculated internally and 15–40 % of those fruit bodies inoculated on the cap surface. The results pointed to a certain resistance of the P. eryngii cap surface to the mycelium of C. mycophilum. Two cropping trials inoculated with C. mycophilum were set up to evaluate the pathogenicity of the causal agent of cobweb in two casings. At the end of the growth cycle, 50–60 % of the inoculated blocks cased with mineral soil, and 20–33 % of the inoculated blocks cased with black peat showed cobweb symptoms. This difference in the appearance of the disease and its aggressiveness may be partly explained by different electrical conductivity values of the casing materials used. In vitro sensitivity of the C. mycophilum isolates and P. eryngii strains against four fungicides (chlorothalonil, prochloraz-Mn, thiabendazole and thiophanate-methyl) was assessed in radial growth experiments on fungicide-amended media. The most effective fungicides for inhibiting the in vitro growth of C. mycophilum were prochloraz-Mn and chlorothalonil, while prochloraz-Mn was also the most selective fungicide between P. eryngii and C. mycophilum, and chlorothalonil was the most toxic fungicide against the P. eryngii mycelium.     

Multi-scale Modeling of Animal Movement and General Behavior Data Using Hidden Markov Models with Hierarchical Structures

Hidden Markov models (HMMs) are commonly used to model animal movement data and infer aspects of animal behavior. An HMM assumes that each data point from a time series of observations stems from one of N possible states. The states are loosely connected to behavioral modes that manifest themselves at the temporal resolution at which observations are made. Due to advances in tag technology and tracking with digital video recordings, data can be collected at increasingly fine temporal resolutions. Yet, inferences at time scales cruder than those at which data are collected and, which correspond to larger-scale behavioral processes, are not yet answered via HMMs. We include additional hierarchical structures to the basic HMM framework, incorporating multiple Markov chains at various time scales. The hierarchically structured HMMs allow for behavioral inferences at multiple time scales and can also serve as a means to avoid coarsening data. Our proposed framework is one of the first that models animal behavior simultaneously at multiple time scales, opening new possibilities in the area of animal movement and behavior modeling. We illustrate the application of hierarchically structured HMMs in two real-data examples: (i) vertical movements of harbor porpoises observed in the field, and (ii) garter snake movement data collected as part of an experimental design. Supplementary materials accompanying this paper appear online.     

Effects of selective cutting and herbicide use in spring barley on seed production of Cirsium arvense

A field experiment was performed in Sweden to evaluate the effect of herbicide treatment and selective cutting on the seed production of Cirsium arvense. Four treatments (control (C), selective cutting (S), early (H1) and late (H2) herbicide application) were laid out in a randomized block experiment. The field was sown with spring barley and contained a natural population of the weed. Treatments were first applied 2015 and repeated 2016. Changes in the number of seeds per flower receptacle and average seed weight were measured over time in 2016 from the onset of seed production until crop harvest. At harvest, number of shoots per area and cumulative numbers of flower receptacles, which had shed mature seeds over the season, were counted. These data were used to assess total seed production over the season. Treatment H2 led to a significantly decreased number of seeds per receptacle (49) compared to S (59), H1 (64) and C (67). Over time and treatment, number of seeds per flower receptacle was lowest in the second week (47) and increased over the third week to 69 in week four. Average weight per seed was about constant over time (0.91?mg) while H1 and S (0.63 and 0.78?mg, respectively) had lower seed weights compared to H2 and C (1.04 and 1.19?mg, respectively). Total seed production over the season in terms of number of seeds per square meter was greatly reduced by all treatments (5–20 seeds m^?2, or 3–14?mg?m^?2) compared to the control (6600 seeds m^?2, or 7800?mg?m^?2). We conclude that seed production of C. arvense is inhibited a thousand-fold and equally well by selective cutting as by early or late herbicide treatments.