Variation in the relationship between ozone exposure and crop yield as derived from simple models of crop growth and ozone impact

Causes of variation in O3 dose-crop yield loss relationship (D-R) were studied with the models of crop growth and O3 effects. In the growth model, biomass accumulation was assumed to be proportional to solar radiation intercepted by the plant leaves. The O3 impact was modeled as a linear function of the O3 concentration less the background O3. The models were combined to give analytical expressions of D-R between mean O3 concentration ( ) and relative yield loss. The effects of O3 on canopy photosynthesis and leaf abscission in reproductive growth were addressed. The O3 impact on photosynthesis was modeled as a reduced canopy light-use efficiency (LUE). The resultant yield loss was proportional to with the modification (M) due to the fluctuations in O3 and a weighting factor (w), and to the correlation between them. The weighting factor is defined as daily biomass accumulation in the background O3. If the sensitivity of canopy LUE is much higher during reproductive growth, the D-R was further modified by the ratio of weighted sum of O3 during reproductive growth to that through a whole season. The D-R for the O3 effect on leaf abscission was a hyperbolic function of with modifications by M. The above analysis thus identified fluctuations in O3 and the weighting factor as possible causes of the variation in the D-R.