Diurnal oscillations of gas production and effluxes (CO2 and CH4) in cores from a peat bog

Feat cores (15 cm diam x 30 cm deep) from Ellergower Moss, New Galloway, Scotland were kept and monitored at constant temperature(10 +/-0.1 degrees C) for gas production using a 1.6 mm diam stainless steel probe fitted with a membrane inlet and connected to a quadrupole mass spectrometer. In the headspace, O-2, CO2 and CH4 (measured at m/z values 32, 44 and 15 respectively) showed diurnal fluctuations in low-intensity natural daylight and under a light-dark (LD, 12:12) regime. Over the first few cycles O-2 and CO2 increased together in the dark and decreased in the light, whereas CH4 showed variations in antiphase with the other two gases. CO2 and CH4 also showed diurnal oscillations at 15 cm depth, but these decreased together in the light whereas argon (m/z = 40) was not varying. A highly-damped free-run of the oscillations in gas concentrations at 15cm depth was evident for only 3 cycles in complete darkness and at constant temperature. This might suggest desynchronization between individual plants with different free-running periods. A hydrocarbon signal (m/z = 26) at 15 cm depth also showed diurnal cycles but out of phase with CO2 and CH4. We postulate a circadian control of microbiological activities imposed by the vascular plants (Carex, Eriophorum, Molinia, Calluna, Erica). Under natural conditions the pronounced temperature sensitivity of CO2 and CH4 emission results in entrainment to daily temperature cycles. The amplitudes of the rhythms are greatest when temperature and light intensity changes are most pronounced, i.e. when the fluctuations in environmental factors are most potent as synchronizers (zeitgebers) and as masking factors.