0002 μmol N2O L−1). However, after 10 days, the O2 concentrations had declined to a mean of 5.6% v/v in all the treatments (Fig. 2a) due to O2 dissolution. N2O concentrations at day 10 in the Protein Tyrosine Kinase inhibitor headspace of the three fungal treatments were 0.0117±0.00015 μmol N2O L−1 (P. involutus), 0.0114±0.0003 μmol N2O L−1 (T. fibrillosa) and 0.0114±0.00043 μmol N2O L−1 (F. lichenicola); there was no difference in the headspace N2O concentrations between the three species. No N2O was detected in the control flasks, which indicates a fungal source for N2O production. N2O production can contribute to cell growth (e.g. Shoun

& Tanimoto, 1991; Zhou et al., 2001); however, the selleck compound energy yield varies between species (Usuda et al., 1995), and further work is required to determine whether N2O production is an energy-yielding process for symbiotic ectomycorrhizal fungi compared with free-living fungi. The CO2 concentrations increased in all the fungal treatments (Fig. 2b), and were significantly higher (P<0.05) in the ectomycorrhizal fungal treatments by day 10. There was a significant decline in the nitrate concentrations over 10 days for P. involutus (Fig. 2c),

resulting in the recovery of 0.006% of the original medium nitrate-N as N2O-N by day 10. Although the final media pH differed significantly between treatments (Fig. 2d), there was no significant change over the incubation period within treatments; hence, it is unlikely that N2O detection can be attributed to abiotic production from nitrite. Caution must be exercised when making direct comparisons with data from other studies, due to the very different culture conditions and growth periods, as our results are below the range of N2O fluxes published thus far, which may range from <100 to 1000 μmol N2O over shorter growth periods PIK-5 than presented here. For example, the maximum N2O production by F.

lichenicola was ∼600 μmol N2O [20 mM NaNO3 with ammonium after 48 h (Fig. 1b; Watsuji et al., 2003)] and F. oxysporum produced ∼800 μmol N2O [after 96 h; 10 mM NaNO3 (Fig. 1a; Shoun & Tanimoto, 1991)]. Further investigation is required to determine ectomycorrhizal fungal N2O production under a wider range of O2, N and C conditions. In our experiment, N2O production was detected when the O2 concentrations were <6% v/v O2 (day 10), suggesting that the two ectomycorrhizal fungi we examined here may possess the ability to reduce nitrate as an alternative respiratory mechanism. This may be of important environmental relevance in situations where CO2 concentrations are particularly high due to, for example, increased microbial activity within the fungal hyphosphere (e.g. Baschien et al., 2009).