Carbon sequestration

Maria-Luisa Gutierrez-Zamora

The JAMS rendezvous this October 31st took place in the fourth floor of the Museum with a magnificent view of Sydney, and began with an ad hoc presentation featuring sulphurous scents and sexy fangs. Katherina Petrou (UTS) initiated us in the science of the sulphur cycle in the oceans and how this process is dominated by the production of dimethylsulfoniopropionate (DMSP) by microalgae and its decomposition into dimethylsulphide (DMS), a strong odorous chemoattractant for a range of marine organisms. In tackling the mystery of how harmful algal blooms disappear, Katherina discovered that DMS produced by the dinoflagellate Alexandrium minutum (causative agent of toxic algal blooms) was the chemical cue for the infection of its parasitoid Parvilucifera sinerae.  An elegant video illustrated how DMS at 300 nM was able to activate the parasitoid spores from a dormant state to leave the sporangium (an infected A. minutum cell) in transit to infect other cells and propagate. Activation only occurred in the range of 30 to 300 nM indicating that the effect was dependent on cell density. Thus, Katherina’s work showed that DMS plays an important role in the biological control of toxic algal blooms in the oceans. Her results contribute to the better understanding of marine chemical ecology.

Event Date: 
Wednesday, October 31, 2012 - 06:15 - 06:30

Impact of nutrient addition on microbial community actively decomposing wheat residues and sequestration of carbon in soil


Soils represent a significant terrestrial carbon reservoir and there is considerable interest in increasing or maintaining its size.   Recent work has suggested that microbially mediated carbon sequestration into soils may be maximised by ensuring adequate supply of other nutrients (nitrogen, phosphorous, sulphur), thus maintaining high microbial carbon use efficiency.  This is particularly important in cropping agriculture systems where appropriate crop-residue management may result in substantial soil carbon and general soil quality improvements.
A soil microcosm experiment was conducted to evaluate the effects of nutrients on the decomposition of wheat residues; specifically the effects on active bacterial community and carbon sequestration.  Stable Isotope Probing (SIP) of 16S rDNA using Phylochip microarrays was employed to investigate the bacterial community associated with the decomposition of 13C-labelled wheat straw and incorporation of the carbon into soil humus.  Respiration and carbon, nitrogen, phosphorous and sulphur transformations were measured over a 56 day incubation to assess priming effects, both gross and net humification efficiency and carbon sequestration through microbiological action.  Soils that received wheat residues only always showed an increase in “new” carbon (13C), although they did not always show an increase in “total” (12C +13C) carbon.  Soils receiving nutrients (nitrogen, phosphorous and sulphur) with wheat residues did show an increase in both new and total carbon pools, suggesting availability of nutrients other than carbon influence soil carbon sequestration.  Bacterial communities responsible for residue decomposition and carbon sequestration were different for nutrient added and no-nutrient treatments, indicating microbial carbon use efficiency is also influenced by the composition of the active community.  Our results suggest that soil carbon:nitrogen:phosphorus:sulphur (C:N:P:S) stoichiometry and bacterial community composition play important roles in determining potential levels of carbon sequestration in agricultural soils.

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