Effects of elevated O3 on soil respiration in a winter wheat - soybean rotation cropland

Abstract

The increasing tropospheric ozone (O3) concentration has been reported to have negative effects on ecosystems. However, few investigations have focussed on the impacts of elevated O3 on soil respiration in cropland. This study aimed to examine the responses of soil respiration to elevated O3 with open-top chambers (OTCs) in a winter wheat (Triticum aestivum L.)–soybean (Glycine max (L.) Merr) rotation. The experiment was performed in the cropland near Nanjing city, south-east China. Seasonal changes in soil respiration rates, soil CO2 production rates, and nitrification and denitrification rates in ambient air (control) and elevated O3 (100 ppb) treatments were investigated in the 2009–10 winter wheat and 2010 soybean growing seasons. Seasonal mean soil respiration rates for the control and 100 ppb treatments were 3.16 and 2.66 μmol/m2.s, respectively, in the winter wheat growing season, and they were 3.59 and 2.51 μmol/m2.s, respectively, in the soybean growing season. Mean soil respiration rate in the control was ~29% higher than that in the 100 ppb treatment across the whole winter wheat–soybean rotation season. Elevated O3 significantly decreased soil respiration in both crops, with a larger effect observed in soybean. Mean soil CO2 production rates were reduced by ~42% in the 100 ppb O3 treatment compared with the control. No O3 effects were observed on soil nitrification and denitrification during the period monitored. A further analysis of covariance showed that soil respiration was significantly correlated with both soil temperature and moisture, and no interaction effects of O3 treatment and covariate (temperature or moisture) were observed.