Ecosystem

Event Date: 
Wednesday, August 28, 2013 - 18:15 - 18:30
Institution: 
CSIRO Canberra
Title: 

Multi-scale spatial patterns of soil microbial communities and biogeochemical processes in three arctic ecosystems

Abstract: 

Microbial communities and their functional role in soil biogeochemical processes vary across spatial scales. Although soil and microbial spatial variability has been studied in various tropical and temperate ecosystems, little information is available from arctic ecosystems. Arctic soils represent a significant proportion of global land mass and contain about one fourth of total soil carbon pool. Soil microbial nitrogen (N) transformations such as nitrification and denitrification have significant implications for N availability and N loss in nutrient-limited arctic ecosystems. This study explored the spatial relationships among microbial communities, functional processes and soil properties in three Canadian arctic ecosystems. Despite adverse climatic conditions and frequent cryopedogenic processes, soil attributes and microbial abundance are highly spatially structured and their spatial autocorrelation is consistent within and between the ecohabitats. However, the zone of spatial autocorrelation is substantially smaller than non-arctic ecosystems. Ammonia-oxidizing and denitrifying communities are spatially structured within 5 m whereas potential nitrification and denitrification are spatially autocorrelated within 40 m in arctic soils. Nitrification activities are driven at small scales (<1 m) by moisture and total organic carbon content whereas gene abundance and other edaphic factors drive at medium (1-10 m) and large (10-100 m) scales. Soil moisture, organic carbon and nitrogen content are the predominant driving factors with nirK abundance also correlated to denitrification across spatial scales. Overall, this study unravels the multi-scale determinants of nitrification and denitrification in Arctic ecosystems.

Event Date: 
Wednesday, March 27, 2013 - 18:15 - 18:30
Institution: 
Hawkesbury Institute for the Environment, University of Western Sydney
Title: 

Effect of Huanglongbing on the structure and functional diversity of microbial communities associated with citrus.

Abstract: 

Plant-microbe interactions lie at the heart of plant performance and ecology. It has been postulated that disruption of multi-trophic interactions in a stable ecosystem under the influence of invading phytopathogens will cause community reorganization and changes in the local feedback interactions. However, there is a paucity of knowledge on the extent to which such community shifts may occur, on the dynamics of changes and on the putative effects regarding the functioning of ecosystems. We have used Citrus-‘Candidatus Liberibacter asiaticus’ [Las, causal agent of devastating Huanglongbing (HLB) disease] as a host pathogen model to characterize the structure, function and interactions of plant-associated microbial communities. We applied a suit of metagenomic techniques to provide detailed census of citrus associated microbiomes. Our results confirmed that Las is the sole causal agent of HLB in Florida and revealed that HLB significantly re-structures the composition of native microbial community present either in leaf, roots and rhizosphere of citrus. Functional microarray (Geochip) and shotgun metagenomic sequencing showed that HLB has severe effects on various functional guilds of bacteria involved in key ecological processes including nitrogen cycling and carbon fixation. Overall, the metagenomic studies provided evidence that change in plant physiology mediated by Las infection could elicit shifts in the composition and functional potential of plant associated microbial communities. In the long term, these fluctuations might have important implications for the productivity and sustainability of citrus producing agro-ecosystems.

 
 
The Summer Course at the Sydney Institute for Marine Science will provide a comprehensive training for students with an interest in marine microbes and ecology. Students with a background in any one of the following areas are encouraged to apply: marine science, ecology, microbiology and biotechnology. 
 
Students will develop an integrative view of the microbes in marine ecosystems in terms of their evolution, diversity, interactions and functional roles. 
 
 

Event Date: 
Wednesday, March 28, 2012 - 19:15 - 20:00
Institution: 
University of Western Sydney
Title: 

Estimating the real contributions of microbial communities to ecosystem functioning

Abstract: 

Microorganisms have important effects on ecosystems via their effects on biogeochemical cycles and the structure of ecological communities. While ecosystem responses can, in part, be predicted by the abundance of particular functional groups, the role of microbial diversity in maintaining ecosystem services is less well understood. Microbial ecologists have generally used two approaches to address this gap. The first correlates structural responses in microbial communities to functional responses across divergent ecosystems, an approach that is susceptible to the influence of confounding factors. The second involves manipulating microbial communities in environments with reduced complexity, which can often get at the mechanisms underlying diversity-function relationships but is likely to overestimate the importance of microbial community structure relative to other environmental drivers. Multimodel inference and model selection in multivariate data represents a promising framework that is, by design, capable of estimating the real contributions of microbial diversity and is compatible with the experimental approaches commonly used by microbial ecologists. These approaches will help to address fundamental questions related to microbial community structure and function and will lead to improved predictions of the consequences of microbial community shifts for ecosystem services.

Event Date: 
Wednesday, February 29, 2012 - 18:00 - 18:30
Institution: 
University of Western Sydney
Title: 

Microbial diversity and ecosystem functions, resilience & recovery: Beyond statistical correlation.

Abstract: 

Microbes are the most dominant and diverse group of organisms on planet Earth. They are pivotal to global ecosystem function, carrying out all critical biogeochemical cycling and directly or indirect shape the Earth’s climate. Despite this, their role is not explicitly considered in climate or ecosystem models. This is largely because of their enormous diversity and the lack of theoretical and experimental approaches to illustrate and quantify the magnitude of microbial regulation of ecosystem functions. There are a growing number of studies that provide evidence of the statistical relationship between microbial community and ecosystem function, but such approaches are unable to differentiate between the correlative and casual effects. In this presentation, using a novel diversity dilution approach, I will illustrate the direct role of microbial diversity and community composition in ecosystem function and sustainability, and argue for their explicit inclusion in predictive models.

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