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Root-associated microbes can alleviate plant abiotic stresses, thus potentially supporting adaptation to a changing climate or to novel environments during range expansion. While climate change is extending plant species fundamental niches northward, the distribution and colonization of mutualists (e.g., arbuscular mycorrhizal fungi) and pathogens may constrain plant growth and regeneration. Yet, the degree to which biotic and abiotic factors impact plant performance and associated microbial communities at the edge of their distribution remains unclear. Here, we use root microscopy, coupled with amplicon sequencing, to study bacterial, fungal, and mycorrhizal root-associated microbial communities from sugar maple seedlings distributed across two temperate-to-boreal elevational gradients in southern Québec, Canada. Our findings demonstrate that soil pH, soil Ca, and distance to sugar maple trees are key drivers of root-associated microbial communities, overshadowing the influence of elevation. Interestingly, changes in root fungal community composition mediate an indirect effect of soil pH on seedling growth, a pattern consistent at both sites. Overall, our findings highlight a complex role of biotic and abiotic factors in shaping tree-microbe interactions, which are in turn correlated with seedling growth. These findings have important ramifications for tree range expansion in response to shifting climatic niches. The analysis of root fungal, mycorrhizal, and bacterial communities of tree seedlings sampled across elevation gradients reveals strong effects of edaphic factors on microbial communities and interactions between root microbes and seedling growth. [ABSTRACT FROM AUTHOR]

The Arctic is warming at an alarming rate. While changes in plant community composition and phenology have been extensively reported, the effects of climate change on reproduction remain poorly understood. We quantified multidecadal changes in flower density for nine tundra plant species at a low- and a high-Arctic site in Greenland. We found substantial changes in flower density over time, but the temporal trends and drivers of flower density differed both between species and sites. Total flower density increased over time at the low-Arctic site, whereas the high-Arctic site showed no directional change. Within and between sites, the direction and rate of change differed among species, with varying effects of summer temperature, the temperature of the previous autumn and the timing of snowmelt. Finally, all species showed a strong trade-off in flower densities between successive years, suggesting an effective cost of reproduction. Overall, our results reveal region- and taxon-specific variation in the sensitivity and responses of co-occurring species to shared climatic drivers, and a clear cost of reproductive investment among Arctic plants. The ultimate effects of further changes in climate may thus be decoupled between species and across space, with critical knock-on effects on plant species dynamics, food web structure and overall ecosystem functioning. [ABSTRACT FROM AUTHOR]

Background: Infrared thermography (IRT) techniques and full-field deformation calorimetry approaches have profoundly impacted the experimental mechanics community. The way in which granular materials are tested is currently excluded from this trend, as evidenced by the small number of papers in the literature mentioning the use of thermographic cameras. Objective: The objective of this work was to perform a thermomechanical analysis of soft granular systems by distinguishing temperature changes associated with thermoelastic coupling (TEC) and mechanical dissipation (MD). Methods: Cyclic confined compression was applied to different granular systems consisting of ellipsoidal cross-section cylinders made of thermoplastic polyurethane. The temperatures measured using IRT were processed to identify the heat associated with TEC and MD, based on considerations of adiabaticity and thermodynamic cycle completion. Various granular configurations and spatial resolutions of the thermal maps were compared. Results: Strong TEC is revealed around the contact areas between all particles, which can be explained by stress concentrations. Strong MD is found around specific contacts, as well as within some particles, which can be explained by viscosity and friction. TEC data was processed for a granular system comprised of about 600 interparticle contacts, providing statistical information. Conclusions: TEC appears to be a strong coupling in the sense that its intensity is much higher than that of the MD. It is shown that IRT provides valuable information at the local scale, namely the signature of reversible (TEC) and irreversible (MD) mechanical phenomena, both at the interparticle contacts and inside the particles. [ABSTRACT FROM AUTHOR]

Understanding how spring phenology influences early life can provide important insights into drivers of future development and survival. We combined unique, long-term data from a bighorn sheep population and satellite-derived phenology indices to quantify the relative importance of maternal and environmental influences on milk composition and lamb overwinter survival. Based on 216 milk samples from 34 females monitored over 6 years, we found that longer snow-free and vegetation growing seasons increased milk fatty acid, iron and lactose concentrations. Structural equation modelling revealed no causality between milk energy content, lamb weaning mass and lamb overwinter survival. Our results suggest that spring conditions can affect milk energy content, but we did not detect any effect on lamb overwinter survival either directly or indirectly through lamb weaning mass. The effect of green-up date on milk composition and energy content suggests that herbivores living in seasonal environments, such as the bighorn sheep, might rely on a strategy intermediate between 'capital' and 'income' breeding when energy demands are high. [ABSTRACT FROM AUTHOR]

Intraguild (IG) predation and interspecific competition may affect the settlement and success of species in their habitats. Using data on forest-dwelling hawks from Finland, we addressed the impact of an IG predator, the northern goshawk Accipiter gentilis (goshawk), on the breeding of an IG prey, the common buzzard Buteo buteo. We hypothesized that the subordinate common buzzard avoids breeding in the proximity of goshawks and that interspecific competitors, mainly Strix owls, may also disturb common buzzards by competing for nests and food. Our results show that common buzzards more frequently occupied territories with a low IG predation threat and with no interspecific competitors. We also observed that common buzzards avoided territories with high levels of grouse, the main food of goshawks, possibly due to a risk of IG predation since abundant grouse can attract goshawks. High levels of small rodents attracted interspecific competitors to common buzzard territories and created a situation where there was not only an abundance of food but also an abundance of competitors for the food. These results suggest interplay between top-down and bottom-up processes which influence the interactions between avian predator species. We conclude that the common buzzard needs to balance the risks of IG predation and interference competition with the availability of its own resources. The presence of other predators associated with high food levels may impede a subordinate predator taking full advantage of the available food. Based on our results, it appears that interspecific interactions with dominant predators have the potential to influence the distribution pattern of subordinate predators. [ABSTRACT FROM AUTHOR]

The mountain pine beetle ( Dendroctonus ponderosae, MPB) has killed millions of lodgepole pine ( Pinus contorta) trees in Western Canada, and recent range expansion has resulted in attack of jack pine ( Pinus banksiana) in Alberta. Establishment of MPB in the Boreal forest will require use of jack pine under a suite of environmental conditions different from those it typically encounters in its native range. Lodgepole and jack pine seedlings were grown under controlled environment conditions and subjected to either water deficit or well watered conditions and inoculated with Grosmannia clavigera, a MPB fungal associate. Soil water content, photosynthesis, stomatal conductance, and emission of volatile organic compounds (VOCs) were monitored over the duration of the six-week study. Monoterpene content of bark and needle tissue was measured at the end of the experiment. β-Phellandrene, the major monoterpene in lodgepole pine, was almost completely lacking in the volatile emission profile of jack pine. The major compound in jack pine was α-pinene. The emission of both compounds was positively correlated with stomatal conductance. 3-Carene was emitted at a high concentration from jack pine seedlings, which is in contrast to monoterpene profiles of jack pine from more southern and eastern parts of its range. Fungal inoculation caused a significant increase in total monoterpene emission in water deficit lodgepole pine seedlings right after its application. By 4 weeks into the experiment, water deficit seedlings of both species released significantly lower levels of total monoterpenes than well watered seedlings. Needle tissue contained lower total monoterpene content than bark. Generally, monoterpene tissue content increased over time independent from any treatment. The results suggest that monoterpenes that play a role in pine-MPB interactions differ between lodgepole and jack pine, and also that they are affected by water availability. [ABSTRACT FROM AUTHOR]

During the last 20 years, ecologists discovered the importance of including spatial relationships in models of species distributions. Among the latest developments in modelling how species are spatially structured are eigenfunction-based spatial filtering methods such as Moran's eigenvector maps (MEM) and principal coordinates of neighbour matrices (PCNM). Although these methods are very powerful and flexible, they are only suited to study distributions resulting from non-directional spatial processes. The asymmetric eigenvector map (AEM) framework, a new eigenfunction-based spatial filtering method, fills this theoretical gap. AEM was specifically designed to model spatial structures hypothesized to be produced by directional spatial processes. Water currents, prevailing wind on mountainsides, river networks, and glaciations at historical time scales are some of the situations where AEM can be used. This paper presents three applications of the method illustrating different combinations of: sampling schemes (regular and irregular), data types (univariate and multivariate), and spatial scales (metres, kilometres, and hundreds of kilometres). The applications include the distribution of a crustacean ( Atya) in a river, bacterial production in a lake, and the distribution of the copepodite stages of a crustacean on the Atlantic oceanic shelf. In each application, a comparison is made between AEM, MEM, and PCNM. No environmental components were included in the comparisons. AEM was a strong predictor in all cases, explaining 59.8% for Atya distribution, 51.4% of the bacterial production variation, and 38.4% for the copepodite distributions. AEM outperformed MEM and PCNM in these applications, offering a powerful and more appropriate tool for spatial modelling of species distributions under directional forcing and leading to a better understanding of the processes at work in these systems. [ABSTRACT FROM AUTHOR]

Two cases of massive pulmonary embolism, confirmed by angiographic or necropsy findings, were remarkable by the absence of arterial hypoxaemia. The various mechanisms responsible for arterial hypoxaemia in pulmonary embolism are discussed. It is suggested that in patients with massive pulmonary embolism a markedly decreased cardiac output might account for the absence of arterial hypoxaemia. In the light of these two cases the finding of a normal PaO2 does not rule out the diagnosis of pulmonary embolism. [ABSTRACT FROM AUTHOR]