RESPONSES OF SOIL RESPIRATION TO THE COORDINATED EFFECTS OF SOIL TEMPERATURE AND BIOTIC FACTORS IN A MAIZE FIELD

Aims Based on the dynamic measurements of soil respiration and its environmental factors in a maize (Zea mays) field during the growing season in 2005, the diurnal and seasonal variations of soil respiration (SR) and their responses to the coordinated effects of soil temperature and biotic factors were studied. Our objective was to describe the effects of biotic factors on the response of soil respiration to soil temperature and to determine the seasonal variation of soil respiration during the growth season of maize. Methods Soil respiration rates were measured twice monthly during the growing season (May-September) in 2005 using a soil respiration chamber (LI-6400-09, Li-Cor Inc., Lincoln, NE) connected to a portable infrared gas analyzer (IRGA, LI-6400, Li-Cor Inc., Lincoln, NE). We inserted 15 soil collars into the soil and soil respiration was pooled over all 15 collars per plot. To catch the diurnal pattern, soil respiration rates were measured every hour from 6∶00 to 18∶00 on May 4, June 5, June 28, July 28, August 28 and September 22. Important findings The diurnal variation of soil respiration showed asymmetric pattern, with the minimum value occurring around 6∶00-7∶00 hours (local time) and the maximum value around 13∶00 hours. Soil respiration fluctuated greatly during the growing season. The mean soil respiration rate was 3.16 μmol CO2·m-2·s-1, with a maximum value of 4.87 μmol CO2·m-2·s-1 on July 28 and a minimum value of 1.32 μmol CO2·m-2·s-1 on May 4. During the diurnal variation of soil respiration, there was a significant linear relationship between soil respiration and soil temperature (T) at 10 cm depth. During the growing season, the coefficients of α and β were fluctuated because the net primary productivity (NPP) of maize markedly increased the slope (α) and the biomass (B) markedly influenced the intercept (β) of the linear equation. Thus, the dynamic model of soil respiration was developed. Most of the temporal variability (97%) in soil respiration could be explained by the variations in soil temperature, biomass and NPP of maize defined in the model. However, just taking account into the influence of soil temperature on soil respiration, an exponential equation over- or underestimated the magnitude of soil respiration.