Conference Presentations by Sue Grayston
Global Soil Biodiversity Initiative 1st conference in Dijon, France
Papers by Sue Grayston
Grassland ecophysiology and grazing ecology, 2000
The effects of defoliation on grass root biomass, distribution, diameter, morphology, growth and ... more The effects of defoliation on grass root biomass, distribution, diameter, morphology, growth and mycorrhizal symbiosis are discussed. Carbon flow in the rhizosphere in response to defoliation, and the effects of grazing on soil microorganisms are described. It is considered that a multidisciplinary approach to research in these areas is required.
Functional diversity in nutrient mobilization by ectomycorrhizal fungi (EcM) has been demonstrate... more Functional diversity in nutrient mobilization by ectomycorrhizal fungi (EcM) has been demonstrated with fungal isolates in microcosms. It remains a challenge to demonstrate this diversity in the field due to the difficulty in locating the exact areas of nutrient mobilization in a complex soil environment and is further complicated by the presence and activity of hyphae from closely related saprotrophic fungal species. In a previous study, we introduced a novel, in-situ imprint method to visualize the locations of soil phosphatase activity present on the soil. By coupling this imprint method with immediate, centimeter-scale soil sampling targeted at the exact areas of phosphatase activity indicated by the imprint, we develop a new method to localize EcM species associated with high rates of phosphatase activity in the field. We tested this targeted sampling method at two scales: at a fine scale within 20 cm x 20 cm imprint plots, and at a landscape scale across replicate age class st...
Ecology
Litter decomposition is a key process that allows the recycling of nutrients within ecosystems. I... more Litter decomposition is a key process that allows the recycling of nutrients within ecosystems. In temperate forests the role of large herbivores in litter decomposition remains a subject of debate. To address this question, we used two litterbag experiments in a quasi-experimental situation resulting from the introduction of Sitka black-tailed deer Odocoileus hemionus sitkensis on forested islands of Haida Gwaii (Canada). We investigated the two main pathways by which deer could modify litter decomposition: change in litter quality and modification of decomposer communities. We found that deer presence significantly reduced litter mass loss after one year, mainly through a reduction in litter quality. This mass loss reflected a 30 and 28 % lower loss of carbon (C) and nitrogen (N), respectively. The presence of deer also reduced the ability of decomposers to breakdown carbon, but not nitrogen. Indeed, litter placed on an island with deer lost 5% less carbon after one year of decomposition than did litter decomposing on an island without deer. This loss in ability to decompose litter in presence of deer was outweighed by the differences in mass loss associated with the effect of deer on litter quality. Additional effects of feces deposition by deer on the decomposition process were also significant but minor. These results suggest that the effects continental-scale dramatic increases in deer populations may have on broad-scale patterns of C and N cycling deserve closer attention.
In temperate forest ecosystems, the role of large herbivores in litter decomposition, a key nutri... more In temperate forest ecosystems, the role of large herbivores in litter decomposition, a key nutrient cycling process, is unresolved. Herbivores may first modify litter abundance by affecting plant cover. They may also modify the decomposition process by changing litter quality and altering decomposers' ability by changing soil abiotic properties and/or decomposer communities. Using two litterbag transplantation experiments in the quasi-experimental situation resulting from the introduction of Sitka black-tailed deer to the forests of Haida Gwaii (Canada), we disentangle the relative importance of the latter modifications on litter decomposition. We demonstrate that deer strongly reduce carbon (C) and nitrogen (N) loss, a 21 and 38 % decrease respectively, mainly by altering plant community composition. We reveal other ecosystem changes induced by deer through feces deposition, abiotic soil modification or decomposer community changes that affect decomposition processes, but are ...
Applied and environmental microbiology, Jan 27, 2017
Fine root litter is the principal source of carbon stored in forest soils and a dominant source o... more Fine root litter is the principal source of carbon stored in forest soils and a dominant source of carbon for fungal decomposers. Differences in decomposer capacity between fungal species may be important determinants of fine-root decomposition rates. Variable-retention harvesting (VRH) provides refuge for ectomycorrhizal fungi, but its influence on fine-root decomposers is unknown, as are the effects of functional shifts in these fungal communities on carbon cycling. We compared fungal communities decomposing fine-roots (in litter bags) under VRH, clearcut, and uncut stands at two sites (6- and 13-years post-harvest), and two decay stages (43-days and 1 year after burial), in Douglas-fir forests in coastal British Columbia, Canada. Fungal species and guilds were identified from decomposed fine-roots using high-throughput sequencing. Variable-retention had short-term effects on β-diversity; harvest treatment modified fungal community composition at the 6-year post-harvest site, but ...
Soil Biology and Biochemistry
Microbial gene markers are hypothesized to be mediating factors between environment factors and m... more Microbial gene markers are hypothesized to be mediating factors between environment factors and methane flux, but mediation is not typically modeled directly in ecosystem studies using graphic models. Structural equation modelling (SEM) was used to test if mcrA and 16S markers were mediating the effects of soil moisture on methane flux in two ecosystem types, Upland and Wetland Forest. SEM results indicated that mcrA functional marker was a mediator in the Upland Forest but not in the Wetland Forest. In the Upland Forest, the 16S marker indirectly effected methane flux though its effect on the mcrA marker. The results suggest that functional genes are mediating drivers in ecosystems where environmental factors are weak drivers of methane fluxes. Our results highlight the importance of testing for microbial indirect pathways in assessing drivers of methane cycling and provide a basis for more complex modelling of mediated pathways in analysis of ecosystem processes.
Applied and environmental microbiology, 2017
The Athabasca oil sand deposit is one of the largest single oil deposits in the world. Following ... more The Athabasca oil sand deposit is one of the largest single oil deposits in the world. Following surface mining, companies are required to restore soil-like profiles that can support the previous land capabilities. The objective of this study was to assess whether the soil prokaryotic alpha diversity (α-diversity) and β-diversity in oil sand soils reconstructed 20 to 30 years previously and planted to one of three vegetation types (coniferous or deciduous trees and grassland) were similar to those found in natural boreal forest soils subject to wildfire disturbance. Prokaryotic α-diversity and β-diversity were assessed using massively parallel sequencing of 16S rRNA genes. The β-diversity, but not the α-diversity, differed between reconstructed and natural soils. Bacteria associated with an oligotrophic lifestyle were more abundant in natural forest soils, whereas bacteria associated with a copiotrophic lifestyle were more abundant in reconstructed soils. Ammonia-oxidizing archaea w...
Soil Biology and Biochemistry, 2016
Tree species can influence rates of soil N transformations, but the question remains whether diff... more Tree species can influence rates of soil N transformations, but the question remains whether differences in N cycling rates are mirrored by the abundance of relevant functional genes. We studied whether the influence of tree species on soil N transformation processes and abundance of functional genes exist across two sites in British Columbia with different N availability. We used the 15 N pool-dilution method to estimate gross rates of ammonification and nitrification in forest floors of four conifers in a common garden experiment. The abundances of bacteria, fungi, nitrification (AOA amoA, AOB amoA) and denitrification (nirS, nirK) genes were determined by qPCR. Western red cedar (Thuja plicata) had the highest rates of gross ammonification and NH4 + consumption, followed by Sitka spruce (Picea sitchensis), hemlock (Tsuga heterophylla), and Douglas-fir (Pseudotsuga menziesii); all species showed net nitrate immobilization. Western red cedar forest floors had the greatest abundance of bacterial 16S genes and ammonia-oxidizing archaea amoA genes. This suggests that tree species foster different abundances of ammonification and denitrification functional groups. Differences in N transformation rates between the sites were related to site N status, as reflected in C:N ratios of the forest floor and microbial biomass, and were more closely tied to rates of N consumption rather than gross mineralization. Rates of most N transformation processes were related to microbial C:N ratio, indicating that the N status of microbes rather than their biomass or activity level determined the rates of N cycling. Ammonification rates were associated with forest floor and microbial biomass C:N ratio as well as bacterial and fungal abundances. Nitrification rates and denitrification gene abundance were associated with microbial biomass C:N ratios and AOA amoA gene abundance. The forest floor's genetic potential for denitrification was positively correlated with its nitrification potential as indicated by ammonia-oxidizer abundance. We conclude that tree species influenced forest floor N cycling and soil microbial gene abundances, and that functional genetics can be useful for exploring mechanistic links between tree species and nitrogen cycling processes.
Journal of Experimental Botany
Canadian Journal of Forest Research
Ce document est protégé par la loi sur le droit d'auteur. L'utilisation des services d'Érudit (y ... more Ce document est protégé par la loi sur le droit d'auteur. L'utilisation des services d'Érudit (y compris la reproduction) est assujettie à sa politique d'utilisation que vous pouvez consulter en ligne.
The understanding of how nitrogen (N) is cycled in forests is important for improving models of g... more The understanding of how nitrogen (N) is cycled in forests is important for improving models of global biogeochemical cycles and potential climate change mitigation practices, as forests can serve as important sinks and sources of greenhouse gases. To determine the role of tree species identity on N cycling we used two sites (one N rich the other N poor) within a common garden experimental forest on Vancouver Island, British Columbia, Canada. We used the 15N pool dilution method to ascertain gross and net rates of N mineralization and nitrification in soils taken from pure stands of four tree species (western red cedar, western hemlock, Douglas-fir, and Sitka spruce). We also measured soil microbial biomass carbon (C) and nitrogen to determine if the microbial pool was storing the 15N by the end of the pool-dilution experiment. We used qPCR to determine the abundance of total bacterial and fungal communities associated with different tree species and also the abundance of functional...
Soil Biology and Biochemistry, 2013
Predicted alterations in belowground plant-allocated C as a result of environmental change may ca... more Predicted alterations in belowground plant-allocated C as a result of environmental change may cause compositional shifts in soil microbial communities, and it has been hypothesized that such alterations will influence C mitigation in forest ecosystems. In order to investigate to what degree living trees influence the abundance and activity of mycorrhizal fungi, saprotrophic fungi, and bacteria we used a geostatistical approach to examine natural abundance stable-isotope-ratios of soil microbial PLFAs, respired CO2, and different soil organic C pools in a 100 point grid extending from an area of retention trees into a clear-cut area. Labile C from trees was the major source of C for the fungal communities and influenced the composition of the microbial community and soil respiration rates up to ten meters into the clear-cut. When the input of labile plant C decreased, it appeared that microorganisms became increasingly dependent on recycled C released during microbial turnover, resulting in a decrease in soil respiration. Our findings demonstrate that plants not only influence the structure and function of soil microbial communities but also act as important regulators of belowground C flux, soil C sequestration and, ultimately, soil C stocks. (c) 2013 Elsevier Ltd. All rights reserved.
Soil Biology and Biochemistry, 2002
The larvae of the crane¯y, Tipula paludosa (Meig.), graze on plant root systems and are a prevale... more The larvae of the crane¯y, Tipula paludosa (Meig.), graze on plant root systems and are a prevalent pest of upland grassland. Using a slant board system, their effect on two pasture species, Trifolium repens L. and Lolium perenne L. were studied. The larvae fed voraciously on the main root axes of T. repens, causing a 15% reduction in primary axis root length. In contrast, there was no overall effect of grazing on root length of L. perenne. However, the proportion of the root system of L. perenne present as laterals was reduced. The plant N content of T. repens was reduced by grazing, possibly due to leakage of N-containing compounds or selectivity of N-rich tissue by the grazing invertebrate. Larvae were larger when fed on T. repens, and their faeces had a higher concentration of bacteria than when fed on L. perenne.
Rhizodeposition is a key process influencing nutrient availability through its stimulation of mic... more Rhizodeposition is a key process influencing nutrient availability through its stimulation of microbial activity in the rhizosphere. Microbial community structure and function in the rhizosphere has been hypothesised to be a consequence of variation in the quantity and quality of rhizodeposition. This paper discusses the character of carbon loss from trees and describes the use of community level physiological profiles (CLPP) to characterise microbial communities from the rhizosphere and rhizoplane of hybrid larch {Larix eurolepis), Sitka spruce (Picea sitchensis), sycamore {Acer pseudoplatanus) and non-rhizosphere (bulk) samples from a farm woodland site. Canonical variate analysis (CVA) was used to analyse the carbon utilisation data and discriminate treatment effects. CVA discriminated the rhizosphere and rhizoplane microbial communities from the bulk soil. The carbon profiles of the rhizosphere microbial communities from the three tree species were similar, but there was significant discrimination of the communities from the three tree rhizoplanes. These differences were mainly attributable to differences in carboxylic acid utilisation. Isolation and enumeration of culturable microorganisms from these soils confirmed the stimulatory effect of the rhizosphere on microbial growth, and in particular on pseudomonad proliferation, and that there are qualitative and quantitative differences in microbial communities associated with these tree species. The possible relationship between microbial diversity and carbon availability in the rhizosphere of different tree species is discussed.
ABSTRACT Canada's ratification of the Kyoto Protocol in 2002 has raised questions of the ... more ABSTRACT Canada's ratification of the Kyoto Protocol in 2002 has raised questions of the role of ecosystem management as a tool to temporarily reduce the net greenhouse gas burden of the forestry industry and potentially generate emission offset credits. We examined growing season methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) fluxes, soil nutrient chemistry, and microbial biomass and CH4-oxidizing bacterial communities in 20-year-old sub-boreal lodgepole pine and maritime hemlock plantations under control conditions and simulated operational fertilization with N (200kg urea-N per ha, applied twice) and N, P, K, and micronutrients. CH4 uptake was significantly greater in the lodgepole pine site than in the hemlock site (152-221 and 57-81 micrograms CH4 consumed per square meter per hour), and there were no significant differences among treatments at either site. Among sites, treatments, and sampling times, CH4 uptake correlated positively with NH4 concentrations and negatively with extractable organic N:P quotients, indicating that this process may potentially be limited by nutrient availability to the CH4-oxidizing bacteria. N2O efflux was measured sporadically at a few flux collars, but was not significantly different from zero at any site, treatment, or time. Soil respiration (CO2 efflux) rates were faster in the hemlock than lodgepole pine site (243-409 and 100-266 milligrams CO2 per square meter per hour), and significant treatment differences were observed at individual times, though with fertilized plots exhibiting both faster and slower rates than controls. Soil respiration correlated significantly with microbial biomass C and N and NO3. Within each site, soil respiration, but not CH4 uptake, was positively correlated with soil temperature. New experiments examining the short-term effects of fertilization on greenhouse gas exchanges are underway, and both short and long-term effects will be evaluated in relation to changes in C storage in plant biomass, litter, and soil organic matter under the same fertilized and control conditions.
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Conference Presentations by Sue Grayston
Papers by Sue Grayston