[Effects of elevated ozone concentration on soil respiration, nitrification and denitrification in a winter wheat farmland].

ABSTRACT

Field experiments were carried out in a winter wheat farmland, in order to investigate the effects of elevated ozone concentration on soil respiration, nitrification and denitrification. Three ozone concentration treatments, which were CK, T1 (100 nL x L(-1)) and T2 (150 nL x L(-1)), were arranged using open top chambers (OTCs). A portable soil CO2 fluxes system was used to measure soil respiration rates. Nitrification and denitrification rates were determined by using a Barometric Process Separation (BaPS) method. Results indicated that there were no significant differences (p > 0.05) in soil respiration rates among CK, T1 and T2 treatments. Mean soil respiration rates for CK, T1 and T2 treatments were (5.36 +/- 0.72), (5.08 +/- 0.04), (4.94 +/- 0.18) micromol x (m2 x s)(-1), respectively. No significant differences (p > 0.05) in mean soil nitrification and denitrification rates were observed between the treatments of CK and T2. During the experimental period, soil respiration showed an exponential relationship with soil temperature for each of the treatment. The Q10 (the respiratory flux at one temperature over the flux at a temperature 10 degrees C lower) values were 1.72, 1.58 and 1.51 for CK, T1 and T2 treatments, respectively. A correlation (Pearson product-momentum correlation) analysis showed that soil water content was correlated significantly (p < 0.05) with soil nitrification (r = 0.828) and denitrification (r = 0.890) rates for CK treatment. Soil water content was correlated significantly (p < 0.05) with soil nitrification rate for T2 treatment, with the correlation coefficient of 0.772. This study indicated that elevated ozone concentration did not significantly affect soil respiration, nitrification and denitrification rates in the winter wheat farmland. Elevated ozone concentration, however, significantly reduced the temperature sensitivity of soil respiration.