The contribution of EcM fungi to forest denitrification has been over-looked, despite the effects EcM fungi have on soil nitrate and C availability, two important factors controlling N<sub>2</sub>O emissions. Although fungal denitrification has been proposed as a significant source of N<sub>2</sub>O in forest soils, the ability for EcM fungi to denitrify is unknown. Here, I test the hypotheses that EcM fungi regulate forest N<sub>2</sub>O production both indirectly by supplying free-living microbes with C through exudation and mycelial turnover, and directly by denitrifying themselves. Soil incubations demonstrated the importance of the quality of C sources released by EcM mycelium in driving denitrification. Comparing N<sub>2</sub>O production from EcM and non-mycorrhizal seedlings showed the potential for the presence of EcM mycelia to increase reduction of <sup>15</sup>N-nitrate to <sup>15</sup>N-N<sub>2</sub>O and <sup>15</sup>N-N<sub>2</sub>. The link to EcM C was confirmed in bacterial culture: denitrification by <i>Paracoccus denitrificans </i>1222 was greatest when using C from extracts of dead mycelium of <i>Paxillus involutus </i>and extrudates produced when the fungus was in symbiosis with a host plant. Therefore, EcM fungi indirectly increase denitrification by providing high quality C. The potential for a direct contribution by EcM fungi to N<sub>2</sub>O production under oxygen-limited conditions was demonstrated in pure cultures of <i>Tylospora fibrillosa </i>and <i>Paxillus involutus. </i>These findings enabled me to develop a schematic model describing the ecological significance of the role of EcM fungi in denitrification in relation to inorganic N availability. Overall, my work provides the first evidence that EcM fungi have the potential to play a key role in N<sub>2</sub>O emissions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:509211 |
| Date | January 2009 |
| Creators | Prendergast-Miller, Miranda T. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=56282 |
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