Stomatal ozone uptake modeling and comparative analysis of flux-response relationships of winter wheat
冬小麦气孔臭氧通量拟合及通量产量关系的比较分析

An Open-Top Chambers(OTCs) experiment on field-grown winter wheat(Triticum aestivum L.) was conducted for the purpose of studing the relationships between stomatal conductance(gs) of wheat flag leaves and different environmental variables.Dose-response analysis was also made in order to compare the performance of flux-based and exposure-based indices in predicting the yield loss of winter wheat.Five different ozone(O3) treatments(Ambient air,AA;Non-filtered air,NF;Non-filtered air with additional O3 of 40 nL/L,NF+40;Non-filtered air with additional O3 of 80 nL/L,NF+80;and Non-filtered air with additional O3 of 120 nL/L,NF+120) were adopted.1471 data points of gs were obtained from twelve measurements through the experiment.Based on the boundary-line analysis,the limiting effects of environmental variables on gs of wheat flag leaves were analyzed.A typical light response curve was found for gs with light saturation at approximately 400 μmol·m-2·s-1 photosynthetically active radiation(PAR).The response of gs to air temperature(T) was characterized by a typical single-peak curve with the physiological optimum temperature at 27 ℃.The critical values for gs responses to water vapor pressure deficit(VPD),soil water potential(SWP) and O3 dose(AOT0) were approximately 1.4 kPa,-100 kPa and 20 μL·L-1·h,respectively,and gs decreased sharply when the critical values were exceeded.A Jarvis type multiplicative model was drawn up and parameterized to predict gs and stomatal O3 uptake(AFstX) of wheat flag leaves from environmental variables(PAR,T,VPD,SWP and AOT0),which were measured continuously through the experiment.Approximately 60% variation of measured gs could be accounted for by the Jarvis type model.Different phenological variations were found for exposure-based indices(AOT40 and SUM06) and flux-based index(AFstX).Due to the variation of gs which was affected by environmental factors and plant development,accumulated stomatal O3 uptake increased nonlinearly during the growing period of wheat flag leaves.The relationship between relative yield loss and accumulated stomatal O3 uptake(AFstX),using a threshold(X) for the O3 uptake rate of 4 nmol·m-2·s-1,provided a higher R2-value(0.76) than AFstX with any other threshold,and this R2-value was between those of relationships based on AOT40(0.74) and SUM06(0.81).Compared to exposure-based indices(AOT40 and SUM06),flux-based index(AFstX) represented no significant advantage for the risk assessment of O3 on winter wheat in our experiment.