Modelling overdispersion with integer-valued moving average processes

A new first-order integer-valued moving average, INMA(1), model based on the negative binomial thinning operation defined by Risti´c et al. [21] is proposed and characterized. It is shown that this model has negative binomial (NB) marginal distribution when the innovations follow a NB distribution and therefore it can be used in situations where the data present overdispersion. Additionally, this model is extended to the bivariate context. The Generalized Method of Moments (GMM) is used to estimate the unknown parameters of the proposed models and the results of a simulation study that intends to investigate the performance of the method show that, in general, the estimates are consistent and symmetric. Finally, the proposed model is fitted to a real dataset and the quality of the adjustment is evaluated.publishe

Effects of Heavy Metals and Arbuscular Mycorrhiza on the Leaf Proteome of a Selected Poplar Clone: A Time Course Analysis

Arbuscular mycorrhizal (AM) fungi establish a mutualistic symbiosis with the roots of most plant species. While receiving photosynthates, they improve the mineral nutrition of the plant and can also increase its tolerance towards some pollutants, like heavy metals. Although the fungal symbionts exclusively colonize the plant roots, some plant responses can be systemic. Therefore, in this work a clone of Populus alba L., previously selected for its tolerance to copper and zinc, was used to investigate the effects of the symbiosis with the AM fungus Glomus intraradices on the leaf protein expression. Poplar leaf samples were collected from plants maintained in a glasshouse on polluted (copper and zinc contaminated) or unpolluted soil, after four, six and sixteen months of growth. For each harvest, about 450 proteins were reproducibly separated on 2DE maps. At the first harvest the most relevant effect on protein modulation was exerted by the AM fungi, at the second one by the metals, and at the last one by both treatments. This work demonstrates how importantly the time of sampling affects the proteome responses in perennial plants. In addition, it underlines the ability of a proteomic approach, targeted on protein identification, to depict changes in a specific pattern of protein expression, while being still far from elucidating the biological function of each protein

Field Performance of alder-Frankia Symbionts for the Reclamation of Oil Sands Sites

The Canadian province of Alberta is the world's largest producer of petroleum products from oil sands exploitation. Oil sands process-affected materials (OSPM), such as tailings sand, produced as a result of bitumen extraction, has low fertility, low organic matter content, it is alkaline, compactable, and contains residual hydrocarbons, making it a very inhospitable growth environment. The petroleum industry is currently involved in efforts to revegetate and remediate the tailings sand. One approach used is revegetation of the reclamation sites with Frankia-inoculated alders. Alders are primary succession trees that have the ability to grow in nutrient poor and waterlogged environments, in part because they form a symbiotic relationship with the nitrogen-fixing Actinobacteria, Frankia. In 2005, field trials were established at Syncrude Canada Ltd. The effect of Frankia-inoculated alders on soil quality was evaluated by monitoring the chemical and microbiological characteristics of the soil. The impact on the indigenous microbial community was also studied using hydrocarbon mineralization assays, and molecular approaches, such as denaturing gradient gel electrophoresis (DGGE). Plant parameters (biomass, nitrogen content) were measured to evaluate the impact of Frankia on alder health and growth. After two growth seasons, Frankia-inoculated and non-inoculated alders yielded comparable amounts of plant biomass and there was an increase in hydrocarbon (hexadecane, naphthalene and phenanthrene) mineralization where the reclamation site had been planted with alder-Frankia. The alder rhizosphere samples all had comparable hydrocarbon mineralization rates. DGGE profiles confirmed a change in the microbial communities of the bulk soil between unplanted and alder-Frankia treatments. Soil tests showed that alder-Frankia decreased soil pH (from 7.5 to 6.6, in 2006, and from 8.2 to 7.2 in 2007) and plant-available sodium content (70% reduction), and had a positive impact on soil organic matter content (increase in up to 6 times in alder-Frankia plots). The field results have confirmed that the alder-Frankia combination results in improved remediation capabilities and enhances soil quality. These improvements in soil quality of the reclamation site provide evidence of the potential of alder-Frankia symbionts to be part of a reclamation strategy for the reforestation of the site, and the re-establishment of a balanced ecosystem. Crown Copyright \ua9 2010.Peer reviewed: YesNRC publication: Ye