Carbon dioxide

Event Date: 
Wednesday, September 30, 2015 - 19:00 - 19:45
Institution: 
University of Southern California
Title: 

Microbial evolutionary surprises in the future ocean:  Long-term adaptation of marine nitrogen-fixing cyanobacteria to high CO2

Abstract: 

The globally-distributed marine cyanobacterium Trichodesmium plays a key role in ocean biogeochemical cycles, as it is a major source of newly fixed atmospheric nitrogen to marine food webs.  Trichodesmium N2 fixation rates have been shown to increase under expected future high carbon dioxide (CO2) levels in short-term studies due to physiological plasticity, but its long-term adaptive responses to ongoing anthropogenic CO2 increases are unknown. My lab has been carrying out a nearly decade-long experimental evolution study with Trichodesmium growing under selection by projected future elevated CO2 levels.  Unexpectedly, selection under high CO2 results in large increases in nitrogen fixation and growth rates that appear to be irreversible, even after adapted cell lines are moved back to lower present day CO2 levels for hundreds of generations. This represents an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained even after returning to the ancestral environment. These constitutive rate increases are accompanied by irreversible shifts in diel nitrogen fixation patterns, up-regulation of cellular energetic pathways, elevated expression of non-coding intergenic DNA, and increased activity of a potentially regulatory DNA methyltransferase enzyme. Ongoing work in my lab is examining the consequences of multiple nutrient limitation interactions (iron and phosphorus) for the physiology, biochemistry and genetics of Trichodesmium adapted to growing in a more nutrient-limited, acidified future ocean environment.  
 

Event Date: 
Wednesday, February 27, 2013 - 15:15 - 15:45
Institution: 
University of Western Sydney
Title: 

Responses of soil fungi to global change: effects of elevated atmospheric CO2, temperature and drought

Abstract: 

Fungi are central to forest carbon and nutrient cycles in Australian sclerophyll forest soils, but little is known about how they will respond to future global change. Our recent research has used a combination of controlled environment glasshouse and field experimentation to investigate the interactive effects of elevated atmospheric CO2 concentration [CO2], increased temperature and drought on Australian eucalypt soil fungal biodiversity.
 
In a glasshouse experiment, seedlings of two eucalypt species (Eucalyptus saligna and E. sideroxylon) were grown in field soil for 5 months under sub-ambient (290 µl l-1), ambient (400 µl l-1) and elevated (650 µl l-1) atmospheric CO2 conditions at both ambient (26°C) and elevated temperature (30°C). Multivariate analyses conducted on molecular data generated from soil and hyphal ingrowth bags (which select for mycorrhizal fungal mycelia) showed a significant (P < 0.035) separation between fungal communities associated with the two different tree species. While there was an effect of [CO2] and temperature, the response was plant species dependent with the exception of the combined elevated [CO2] and elevated temperature treatment (650 µl l-1 CO2 and 30oC) which clustered together regardless of tree species.
 
In the field experiment, E. saligna trees were grown in 12 whole tree chambers for three years under controlled temperature conditions and exposed to either ambient (ca. 380 µl l-1) or elevated (ca. 640 µl l-1) atmospheric [CO2] and different watering regimes to simulate drought. Multivariate analyses of molecular data showed that elevated [CO2] intensified the effect of drought stress by significantly altering fungal community composition.
 
Collectively, our data demonstrate that alterations to atmospheric [CO2], temperature and drought conditions modify soil fungal communities associated with Australian eucalypts. We are currently investigating the knock-on effects of these changes for fungal driven soil processes given the potential for soil microorganisms to significantly influence the direction and magnitude of terrestrial ecosystem/atmosphere feedbacks that regulate global change.

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