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 O-3 dose-crop yield loss relationship (D-R) were studied with the models of crop growth and O-3 effects. In the growth model, biomass accumulation was assumed to be proportional to solar radiation intercepted by the plant leaves. The O-3 impact was modeled as a linear function of the O-3 concentration less the background O-3. The models were combined to give analytical expressions of D-R between mean O-3 concentration ((Q) over bar) and relative yield loss. The effects of O-3 on canopy photosynthesis and leaf abscission in reproductive growth were addressed. The O-3 impact on photosynthesis was modeled as a reduced canopy light-use efficiency (LUE). The resultant yield loss was proportional to (Q) over cap with the modification (M) due to the fluctuations in O-3 and a weighting factor (w), and to the correlation between them. The weighting factor is defined as daily biomass accumulation in the background O-3. 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 O-3 during reproductive growth to that through a whole season. The D-R for the O-3 effect on leaf abscission was a hyperbolic function of (Q) over bar with modifications by M. The above analysis thus identified fluctuations in O-3 and the weighting factor as possible causes of the variation in the D-R. Copyright (C) 1996 Elsevier Science Ltd.