Daytime and Phenological Characteristics of O-3 and CO2 Fluxes of Winter Wheat Canopy Under Short-Term O-3 Exposure

摘要

To analyze the daytime and phenological variations of canopy O-3 and CO2 uptake of winter wheat, the canopy fluxes of wheat plants were measured using a chamber system with four different O-3 levels (0, 40, 80, and 120 nmol mol(-1)) being applied. During the daytime (7: 30-18: 00 hours), canopy fluxes usually peaked around noon in early growing stages, while a generally decreasing trend from morning to afternoon was observed in the later stages. O-3 and CO2 fluxes were positively and negatively correlated with O-3 concentration, respectively. Significant differences were observed in O-3 fluxes but CO2 fluxes among O-3 treatments. Photosynthetically active radiation (PAR) and vapor pressure deficit (VPD) could affect canopy gas uptake in opposite ways. On the phenological timescale, both O-3 and CO2 fluxes followed the variation of leaf area index (LAI) with the maximum occurring simultaneously at the booting stage. The daytime mean fluxes varied from -10.6 to -17.2 nmol m(-2) s(-1) for O-3 and from -5.9 to -19.6 mu mol m(-2) s(-1) for CO2. Quantitatively important O-3 deposition (-3.1 similar to-11.6 nmol m(-2) s(-1)) was also observed at night with the ratios being about 40 similar to 70 % relative to the daytime O-3 fluxes for most measuring days, which indicates a significant contribution from non-stomatal components to canopy O-3 removal. This study confirms that environmental variables and plant phenology are important factors in regulating canopy O-3 and CO2 uptake. O-3 exposure (<= 120 nmol mol(-1)) could not significantly affect the CO2 uptake of wheat canopy in a short time (ca. 10 min).