University of Guelph

About: University of Guelph is a education organization based out in Guelph, Ontario, Canada. It is known for research contribution in the topics: Population & Poison control. The organization has 26542 authors who have published 50553 publications receiving 1715255 citations. The organization is also known as: U of G & Guelph University.

Crop residue influence on denitrification, N2O emissions and denitrifier community abundance in soil

Abstract: Bacterial denitrification plays an important role in the global nitrogen cycle and is a principal contributor of nitrous oxide (N2O) to the atmosphere. The influence of simple (glucose) and complex (red clover and barley residue) carbon (C) sources on the amount of denitrification, N2O molar ratio (N2O:(N2 + N2O)), and abundance of soil total bacterial and denitrifier communities was investigated using repacked soil cores. Quantitative PCR was used to determine the abundance of the total bacterial community (16S rRNA gene) and components of the denitrifier community, cnorBP (Pseudomonas mandelii and related species), cnorBB (Bosea/Bradyrhizobium/Ensifer spp.) and nosZ gene bearing communities. The relationship between the supply of, and demand for, terminal electron acceptors (TEAs), as determined by the relative availability of C and nitrate (NO3−), influenced the amount of denitrification and the N2O molar ratio for both simple and complex C sources. Addition of glucose and red clover to the soil increased microbial activity, leading to NO3− depletion and an increased consumption of N2O, whereas in soil amended with barley straw, there was not sufficient stimulation of microbial activity to create sufficient TEA demand to cause a measurable increase in emissions. This resulted in a higher N2O molar ratio at the end of the incubation for the barley straw amended soil. A significant relationship (R2 = 0.83) was found between respiration and cumulative denitrification, suggesting that the available C increased microbial activity and O2 consumption, which led to conditions favorable for denitrification. The source of C did not significantly affect the total bacterial community or the nosZ copy numbers with an average of 4.9 × 107 16S rRNA gene copies g−1 dry soil and 4.6 × 106 nosZ gene copies g−1 dry soil, respectively. The addition of red clover plus NO3− significantly increased the cnorBP denitrifier community in comparison with the unamended control while the density of the cnorBP denitrifier community increased from 3.9 × 104 copies g−1 dry soil to a maximum of 8.7 × 105 copies g−1 dry soil following addition of glucose plus NO3− to soil. No significant correlations were found between the denitrifier community densities and cumulative denitrification or N2O emissions, suggesting that the denitrification activity was decoupled from the denitrifier community abundance.

Environmental and physical controls on northern terrestrial methane emissions across permafrost zones

Abstract: Methane (CH4) emissions from the northern high-latitude region represent potentially significant biogeochemical feedbacks to the climate system. We compiled a database of growing-season CH4 emissions from terrestrial ecosystems located across permafrost zones, including 303 sites described in 65 studies. Data on environmental and physical variables, including permafrost conditions, were used to assess controls on CH4 emissions. Water table position, soil temperature, and vegetation composition strongly influenced emissions and had interacting effects. Sites with a dense sedge cover had higher emissions than other sites at comparable water table positions, and this was an effect that was more pronounced at low soil temperatures. Sensitivity analysis suggested that CH4 emissions from ecosystems where the water table on average is at or above the soil surface (wet tundra, fen underlain by permafrost, and littoral ecosystems) are more sensitive to variability in soil temperature than drier ecosystems (palsa dry tundra, bog, and fen), whereas the latter ecosystems conversely are relatively more sensitive to changes of the water table position. Sites with near-surface permafrost had lower CH4 fluxes than sites without permafrost at comparable water table positions, a difference that was explained by lower soil temperatures. Neither the active layer depth nor the organic soil layer depth was related to CH4 emissions. Permafrost thaw in lowland regions is often associated with increased soil moisture, higher soil temperatures, and increased sedge cover. In our database, lowland thermokarst sites generally had higher emissions than adjacent sites with intact permafrost, but emissions from thermokarst sites were not statistically higher than emissions from permafrost-free sites with comparable environmental conditions. Overall, these results suggest that future changes to terrestrial high-latitude CH4 emissions will be more proximately related to changes in moisture, soil temperature, and vegetation composition than to increased availability of organic matter following permafrost thaw.

ModDrop: Adaptive Multi-Modal Gesture Recognition

Abstract: We present a method for gesture detection and localisation based on multi-scale and multi-modal deep learning. Each visual modality captures spatial information at a particular spatial scale (such as motion of the upper body or a hand), and the whole system operates at three temporal scales. Key to our technique is a training strategy which exploits: i) careful initialization of individual modalities; and ii) gradual fusion involving random dropping of separate channels (dubbed ModDrop ) for learning cross-modality correlations while preserving uniqueness of each modality-specific representation. We present experiments on the ChaLearn 2014 Looking at People Challenge gesture recognition track, in which we placed first out of 17 teams. Fusing multiple modalities at several spatial and temporal scales leads to a significant increase in recognition rates, allowing the model to compensate for errors of the individual classifiers as well as noise in the separate channels. Futhermore, the proposed ModDrop training technique ensures robustness of the classifier to missing signals in one or several channels to produce meaningful predictions from any number of available modalities. In addition, we demonstrate the applicability of the proposed fusion scheme to modalities of arbitrary nature by experiments on the same dataset augmented with audio.

Identifying Canadian mosquito species through DNA barcodes

Abstract: A short fragment of mt DNA from the cytochrome c oxidase 1 (CO1) region was used to provide the first CO1 barcodes for 37 species of Canadian mosquitoes (Diptera: Culicidae) from the provinces Ontario and New Brunswick. Sequence variation was analysed in a 617-bp fragment from the 5' end of the CO1 region. Sequences of each mosquito species formed barcode clusters with tight cohesion that were usually clearly distinct from those of allied species. CO1 sequence divergences were, on average, nearly 20 times higher for congeneric species than for members of a species; divergences between congeneric species averaged 10.4% (range 0.2-17.2%), whereas those for conspecific individuals averaged 0.5% (range 0.0-3.9%).