Robert L. Bradley's research while affiliated with Université de Sherbrooke and other places

Publications (113)

Article
Full-text available
Moss‐associated cyanobacteria nitrogen (N2‐) fixation can contribute to support moss growth and constitutes a major source of new N in boreal forest ecosystems. The biomass of moss‐colonizing cyanobacteria and their N2‐fixation are usually considered linearly correlated. Yet, recent evidence has shown that cyanobacterial biomass and N2‐fixation can...
Article
Full-text available
AimsWe explored how long-term agricultural practices affect arbuscular mycorrhizal (AM) fungal traits and community structure.Methods We sampled soil and roots from a 26-year-old field experiment comprising 16 replicated treatments, in which we manipulated tillage intensity (moldboard vs. chisel plow), fertilization (organic vs. mineral) and crop r...
Article
The contribution of Coarse Woody Debris (CWD) to N inputs in boreal ecosystems has been reported in intensively managed Scandinavian forests in Europe and in Pacific coastal rainforest in North America. These estimates range from 0.085 to 2 kg N ha⁻¹ y⁻¹. Data from Eastern Canadian forests that receive fewer sylvicultural treatments than do Scandin...
Article
Full-text available
Earthworms are an important soil taxon as ecosystem engineers, providing a variety of crucial ecosystem functions and services. Little is known about their diversity and distribution at large spatial scales, despite the availability of considerable amounts of local-scale data. Earthworm diversity data, obtained from the primary literature or provid...
Article
Full-text available
Earthworms are an important soil taxon as ecosystem engineers, providing a variety of crucial ecosystem functions and services. Little is known about their diversity and distribution at large spatial scales, despite the availability of considerable amounts of local-scale data. Earthworm diversity data, obtained from the primary literature or provid...
Article
Knowledge is lacking on the factors controlling the structure and spatial distribution of earthworm communities within agroecosystems. We first hypothesized that forested riparian buffer strips (FRBS) within agricultural landscapes would be a refuge for earthworms, as we predicted higher soil moisture and organic matter inputs in FRBS than in adjac...
Article
Many laboratory and mesocosm studies have demonstrated that earthworms influence nitrogen (N) cycling reactions that produce nitrous oxide (N2O) in well-aerated soils, but whether earthworms can stimulate N2O fluxes in realistic field conditions remains to be determined. We conducted two field experiments in southern Quebec in perennial forage agro...
Article
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The increase in soil organic matter mineralization rate in boreal forests that may result from global warming is a major concern as it could release large amounts of C to the atmosphere. On the other hand, this may also release N to the soil and stimulate tree growth, which could partly offset the C losses from the soil. The long-term interaction b...
Article
Soils systems provide essential ecosystem functions and services performed by a hyperdiverse array of fauna, but how soil communities respond to climate change remains an understudied topic. Although previous long-term studies have found variable effects of climate change manipulations on soil communities, precipitation often yields strong response...
Article
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In the province of Québec (Canada), pre-commercial thinning (PCT) is a common silvicultural practice applied to young black spruce (Picea mariana (Mill.) BSP) stands. PCT removes some of the competing vegetation and smaller black spruce stems, in order to improve growth rates and reduce forest rotation intervals. It is uncertain whether this positi...
Article
Boreal ericaceous shrubs, such as Kalmia angustifolia, have evolved various traits allowing them to interfere with the growth of conifer trees. These include the ability to spread through rhizomatous growth and to produce high amounts of tannins that interfere with soil N cycling. We examined how pre-commercial thinning (PCT) of young black spruce...
Article
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Inorganic N fertilizers are commonly used in commercial blueberry fields; however, this form of N can favor increased weed species’ growth, which can ultimately reduce the benefits of fertilization. We hypothesized that chipped ramial wood (CRW) compost is an effective alternative organic fertilizer for blueberry plants when weeds are present, as e...
Article
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The forest floor of boreal forest stores large amounts of organic C that may react to a warming climate and increased N deposition. It is therefore crucial to assess the impact of these factors on the temperature sensitivity of this C pool to help predict future soil CO2 emissions from boreal forest soils to the atmosphere. In this study, soil warm...
Data
This PDF file includes: Materials and Methods Supplementary Text Figs. S1 to S6 Tables S1 to S4 References
Article
Full-text available
Soil organisms, including earthworms, are a key component of terrestrial ecosystems. However, little is known about their diversity, their distribution, and the threats affecting them. We compiled a global dataset of sampled earthworm communities from 6928 sites in 57 countries as a basis for predicting patterns in earthworm diversity, abundance, a...
Article
Full-text available
Soil organisms, including earthworms, are a key component of terrestrial ecosystems. However, little is known about their diversity, their distribution, and the threats affecting them. We compiled a global dataset of sampled earthworm communities from 6928 sites in 57 countries as a basis for predicting patterns in earthworm diversity, abundance, a...
Data
This PDF file includes: Materials and Methods Supplementary Text Figs. S1 to S6 Tables S1 to S4 References
Article
Full-text available
Soil organisms, including earthworms, are a key component of terrestrial ecosystems. However, little is known about their diversity, their distribution, and the threats affecting them. We compiled a global dataset of sampled earthworm communities from 6928 sites in 57 countries as a basis for predicting patterns in earthworm diversity, abundance, a...
Data
This PDF file includes: Materials and Methods Supplementary Text Figs. S1 to S6 Tables S1 to S4 References
Data
This PDF file includes: Materials and Methods Supplementary Text Figs. S1 to S6 Tables S1 to S4 References
Article
Full-text available
Soil organisms, including earthworms, are a key component of terrestrial ecosystems. However, little is known about their diversity, their distribution, and the threats affecting them. We compiled a global dataset of sampled earthworm communities from 6928 sites in 57 countries as a basis for predicting patterns in earthworm diversity, abundance, a...
Data
This PDF file includes: Materials and Methods Supplementary Text Figs. S1 to S6 Tables S1 to S4 References
Article
Full-text available
1.Understanding the factors and mechanisms driving the structure of ecological networks is a challenge for community ecologists. Notably, it remains unclear whether observed interaction patterns between two trophic groups are a result of (1) preferential partner selection between groups, or (2) species interactions within groups. 2.We conducted an...
Poster
Full-text available
The boreal forest represents ~50% of the world forest, and 30% is in Canada. It contributes to the storage of 0.5 Peta grams of C per year (1015 g/an). Primary production in boreal forests is strongly limited by nitrogen bioavailability. Although boreal soils are rich in organic nitrogen, its bioavailability is low due to slow decomposition at thes...
Article
We hypothesized that the rhizosphere priming effect (RPE) of soil organic matter by mutant barley lacking root hairs is dependant on a large network of symbiotic arbuscular mycorrhizal fungi (AMF). We thus predicted that fertilizing with phosphate-P would reduce AMF abundance and, in turn, reduce RPE of mutant barley. We packed microcosms with a P-...
Data
Aboveground vegetative biomass (AGVBM) and belowground biomass (BGBM) N content (g N m-2) in the three study plant species. (a–d) N content in lowbush blueberry (LB) AGVBM and BGBM in mixtures with poverty oat grass (POG; dark grey bars) or sweet fern (SF; light grey bars). (e–h) N content in POG and SF AGVBM and BGBM in mixtures with LB. Values ar...
Data
Results of analysis of covariance (ANCOVA) conducted on plants’ aboveground vegetative biomass (AGVBM) production. Plant species was used as a categorical variable and the percentage of fertilizer-derived N recovered (PFNR) in plants as a covariate. (DOCX)
Article
Full-text available
Numerous studies have speculated that lowbush blueberry (Vaccinium angustifolium) is less efficient than weed species at taking up inorganic nitrogen (N) derived from fertilizers, thus raising questions as to the effectiveness of N fertilization in commercial fields. However, competition for acquiring N as well as specific interactions between blue...
Data
Soil characteristics in the study lowbush blueberry field. Data are shown for the two areas of the field where the plots were located: the area colonized by sweet fern and the area colonized by poverty oat grass. (DOCX)
Data
Raw data for N concentration (%) and 15N/14N ratio in the aboveground and belowground biomass (g m-2) of lowbush blueberry, sweet fern and poverty oat grass as a function of weed density level and companion species. (XLSX)
Data
Results of an analysis of covariance (ANCOVA) conducted on the percentage of fertilizer-derived N recovered (PFNR) in plants. Plant species was used as a categorical variable and the belowground biomass (BGBM) as a covariate. (DOCX)
Data
Aboveground and belowground biomass (g m-2), N concentration (%) and percentage of fertilizer-derived N recovered [PFNR (%)] in lowbush blueberry, sweet fern and poverty oat grass as a function of weed density level and companion species. (CSV)
Article
Wind exposure may reduce the snowpack and increase frost damage to lowbush blueberry (Vaccinium angustifolium Ait.). Farmers in the Saguenay-Lac-Saint-Jean region (Québec) have therefore installed natural windbreaks to maintain a deep snow cover. We verified the efficiency of 39 windbreaks distributed over two farms. Over two consecutive years, sno...
Article
Full-text available
Kalmia angustifolia is a boreal ericaceous shrub that can rapidly spread on black spruce forest cutovers in eastern Canada, where CPRS (i.e. Cutting with Protection of Regeneration and Soils”) is practiced. The proliferation of Kalmia often coincides with a reduction in the growth rate of regenerating black spruce seedlings. We report on a study wh...
Article
Biological nitrogen fixation (BNF) by moss-associated cyanobacteria may represent up to 30% of the total nitrogen (N) input in unfertilized boreal forests. It remains difficult, however, to obtain reliable estimates of BNF at the landscape scale due to high spatial variability of BNF at lower scales where it is usually measured. Here we identify mo...
Article
A study was undertaken to test the effects of molybdenum (Mo) and phosphorus (P) amendments on biological nitrogen (N) fixation (BNF) by boreal forest moss-associated cyanobacteria. Feather moss (Pleurozium schreberi) samples were collected on five sites, on two dates and at different roadside distances (0-100m) corresponding to an assumed gradient...
Article
Full-text available
Lowbush blueberry is an important crop in the Saguenay–Lac-Saint-Jean region of Quebec. Accurate evaluation of agronomic practices currently requires destructive sampling and loss of productive fields. We showed that the point intercept method is a rapid and reliable nondestructive alternative for predicting biomass and yield of lowbush blueberry a...
Article
Tree-based intercropping (TBI) may increase carbon (C) sequestration in agroecosystems, but may reduce crop yields. In this study of TBI, we used ecosys, a comprehensive mathematical model of terrestrial ecosystems, which represents interspecific competition for light, nutrients, and water, to evaluate the concurrent effects of TBI on C sequestrati...
Article
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Tree-based intercropping (TBI) systems have shown some promise in mitigating greenhouse gas 16 emissions, such as by sequestering carbon and decreasing soil nitrous oxide emissions. However, 17 the effects of TBI on soil methane fluxes remain unknown. In a field study, we failed to show 18 differences in soil CH4 production between TBI and conventi...
Article
Tree-based intercropping (TBI) system has been suggested as an alternative to conventional monocropping (CM) for decreasing overall greenhouse gas (GHG) emissions. However, little is known about the advantages of TBI compared with organic CM system with low fertilizer inputs. This project compared CO2 and N2O dynamics in replicated TBI and CM in Sa...
Article
Biological nitrogen fixation (BNF) performed by moss-associated cyanobacteria is one of the main sources of new nitrogen (N) input in pristine, high-latitude ecosystems. Yet, the nutrients that limit BNF remain elusive. Here, we tested whether this important ecosystem function is limited by the availability of molybdenum (Mo), phosphorus (P), or bo...
Article
In vitro digestion assays provide useful data for wild ruminant ecologists. It remains highly constraining, however, to conduct these assays in the field. We evaluated various proxies for in vitro digestion assays that use ruminal liquor from wild ruminants. The ruminal liquor of freshly killed white-tailed deer (Odocoileus virginianus) was used to...
Article
The rhizosphere is known as the most active biogeochemical layer of the soil. Therefore, it could be a beneficial environment for biotic methane oxidation. The aim of this study was to document - by means of batch incubation tests - the kinetics of CH4 oxidation in rhizosphere soils that were previously exposed to methane. Soils from three pre-expo...
Article
Full-text available
Since agriculture directly contributes to global anthropogenic greenhouse gas (GHG) emissions, integrating trees into agricultural landscapes through agroforestry systems is a viable adaptive strategy for climate change mitigation. The objective of this study was to evaluate the carbon (C) sequestration and financial benefits of C sequestration acc...
Article
Plants and their microbial symbionts are often found to interact non-randomly in nature, but we have yet to understand the mechanisms responsible for such preferential species associations. Theory predicts that host plants should select symbiotic partners bearing traits complementary to their own, as this should favor cooperation and evolutionary s...
Article
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On Anticosti Island (Quebec, Canada), overbrowsing by white-tailed deer (Odocoileus virginianus) has substantially modified plant communities and reduced the recruitment of balsam fir (Abies balsamea) seedlings over most of the territory. An exception to this phenomenon has been observed in localised patches occurring on a single geological deposit...
Article
Plants are routinely colonized by both beneficial and detrimental microorganisms. These two microbial guilds may indirectly interact with each other via their host, either by modifying its vigor, or by altering its hormonal/defense status. Here, we studied indirect interactions between arbuscular mycorrhizal (AM) fungi and three plant pathogens. We...
Article
It is often reported in the technical literature that the presence of vegetation improves the methane oxidation efficiency of biosystems; however, the phenomena involved and biosystem performance results are still poorly documented, particularly in the field. This triggered a study to assess the importance of vegetation in methane oxidation efficie...
Article
Estimating future fluxes of CH4 between land and atmosphere requires well-conceived process-based biogeochemical models. Current models do not represent the anaerobic oxidation of methane (AOM) in land surface soils, in spite of increasing evidence that this process is widespread. Our objective was to determine whether AOM, or potential AOM, common...
Article
An important asset for the management of wild ungulates is recognizing the spatial distribution of forage quality across heterogeneous landscapes. To do so typically requires knowledge of which plant species are eaten, in what abundance they are eaten, and what their nutritional quality might be. Acquiring such data, however, may be difficult and t...
Article
Full-text available
An important asset for the management of wild ungulates is recognizing the spatial distribution of forage quality across heterogeneous landscapes. To do so typically requires knowledge of which plant species are eaten, in what abundance they are eaten, and what their nutritional quality might be. Acquiring such data, however, may be difficult and t...
Article
Full-text available
Nutrient cycling in riparian buffers is partly influenced by decomposition of crop, grass, and native tree species litter. Nonnative earthworms in riparian soils in southern Quebec are expected to speed the processes of litter decomposition and nitrogen (N) mineralization, increasing carbon (C) and N losses in gaseous forms or via leachate. A 5-mon...
Article
Full-text available
Overbrowsing by white-tailed deer (Odocoileus virginianus Zimmermann) on Anticosti Island (Canada) created a need to develop efficient methods for estimating their foraging patterns. We tested the ability of near infrared (NIR) spectra of feces and of fecal chemical properties to predict diet composition of different individuals. We first used a pr...
Article
A majority of plant species has roots that are colonized by both arbuscular mycorrhizal (AM) and non-mycorrhizal (NM) fungi. The latter group may include plant mutualists, commensals, parasites and pathogens. The co-occurrence of these two broad groups may translate into competition for root volume as well as for plant-derived carbon (C). Here we p...
Article
Fertilizing soils with animal excrements from farms with common antibiotic use represents a risk of disseminating antibiotic resistance genes into the environment. In the case of tetracycline antibiotics, it is not clear, however, whether the presence of antibiotic residues further enhances the gene occurrence in manured soils. We established a mic...
Article
Despite the growing appreciation for the functional diversity of arbuscular mycorrhizal (AM) fungi, our understanding of the causes and consequences of this diversity is still poor. In this opinion article, we review published data on AM fungal functional traits and attempt to identify major axes of life history variation. We propose that a life hi...
Article
Anaerobic oxidation of methane (CH4) (AOM) is a process that was first reported to occur in deep anoxic marine sediments. In this environment, CH4 is oxidized with sulphate (SO42-) as the terminal electron acceptor. It is mediated by a syntrophic consortium formed by SO42- reducing bacteria and anaerobic CH4 oxidizing Archaea, or by the latter alon...
Article
Plant roots provide various forms of soil labile carbon (i.e., rhizodeposition), which stimulate the growth of heterotrophic bacteria in the rhizosphere. This, in turn, provides a food source for phagotrophic protozoa and other bacterivores, whose carbon:nutrient ratios are generally higher than those of their food source. In order to maintain thei...
Article
The intensity of boreal forest wildfires is highly variable, such that natural wood charcoal can be produced at different peak temperatures. This, in turn, may have consequences on the physico-chemical and functional properties of the charcoal that is returned to soil. We report on a microcosm study where black spruce wood charcoal produced at five...
Article
Full-text available
Plants acclimate to nitrogen (N) or moisture stress by respectively increasing photosynthetic N use efficiency (PNUE) or water use efficiency (WUE), in order to maximize their relative growth rate (RGR). These two phenotypic adaptations have opposite effects on specific leaf area (SLA). Thus, intraspecific variations in the SLA-RGR relationship sho...
Chapter
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The purpose of this chapter is to describe the history and current status of agroforestry research and practices across Canada and provide recommendations as “the way forward.” Each of the five regions (the Atlantic Region, Quebec, Ontario, the Prairies, and British Columbia) has unique climates, soils, landforms, and natural resource management sy...
Conference Paper
Background/Question/Methods Arbuscular mycorrhizal (AM) fungi are ubiquitous soil fungi that live symbiotically in roots of a majority of terrestrial plant species. Due to a lack of understanding of AM fungal life history strategies, we still have very little power to predict the outcome of mutualistic interactions between plant and AM fungal ind...
Article
a b s t r a c t The effects of earthworms on soil CH 4 emissions remain ambiguous, as previous studies revealed both positive and negative effects on net rates of CH 4 production. These differences may be linked to land-use history such as pasturing intensity, as the treading of livestock and the input of faeces will affect physical and chemical so...
Article
The practice of careful logging has been mandated in northeastern Canada’s coniferous and mixedwood forests as a means of protecting natural regeneration while minimizing soil disturbance by machinery. This practice imposes evenly spaced, parallel trails for circulation of harvesting machinery, while most of the understory and soil is left intact i...