NUMERICAL SIMULATION STUDY ON THE IMPACTS OF CHANGES OF  TROPOSHERE O3 AND CO2 CONCENTRATIONS ON WINTER WHEAT: ⅡSIMULATION RESULTS AND ANALYSES

With the rapid development of industrialization and urbanization, the incr ease of the troposphere ozone and carbon dioxide concentration at striking rates has adverse effects on biosphere, especially on crops. It is generally accepted that the increase of carbon dioxide concentration has beneficial effects on pla nt productivity while ozone is reported as the air pollutant most damaging to ag ricultural crops and other plant. The Model of Carbon and Nitrogen Biogeochemistry in Agroecosystems (DNDC) is adapted to evaluate simultaneously impacts of climate change on winter wheat. Growth development and yield formation of winter wh eat under different O3 and CO2 concentration conditions were simulated with the improved DNDC model which structure has been described in another paper. Through adjusting the DNDC model applicability, winter wheat growth and development in Gucheng station was simulated well in 1993 and 1999, which was in favor of modif ying the model further. The model was validated against experiment observation, including development stage data, leaf area index, single organ biomass and total aboveground biomass. Sensitivity tests demonstrated that the simulated results in development stage, biomass were sensitive to temperature change. The main co nclusions of the paper were as follows: (1) Growth and yield of winter wheat under CO2 concentration of 500×10-6 (V/V), 700×10-6 (V/V) and the curr ent ozone conc entration was simulated respectively by the model. The results were well fitted with the observed values from the OTCs experiment. The results indicated that th e increase of concentration of CO2 may improve the growth of winter wheat and el evate the yield. (2) The growth and yield of winter wheat under O3 concentrati on of 50×10-9 (V/V)，100×10-9 (V/V)，200×10-9(V/V) and the curre nt CO2 concentra tion were simulated respectively by the model. The simulated curves of the growt hs of stem, leaf and spike organs as well as leaf area index were well in agreem ent with the observed data. The results revealed that ozone has a detrimental ef fect on the growth and yield of winter wheat. Ozone accelerated the process of leaf senescence and caused the loss of the yield. Under very high ozone concentra tion, crops were affected dramatically and even dead. (3) At last, by the model the possible effects of changes of air temperature and the combined effects of O3 and CO2 were estimated respectively. The results showed that doubled CO 2 concentration may alleviate the negative effect of O3 on biomass and yield of winter wheat when ozone concentration was about 70×10-9～80×10-9 ( V/V). The obverse effects of CO2 were less than the adverse effects of O3 when the concentration of ozone is up to 100×10-9 (V/V). Future work should determine whether it is applied to other species by adjusting the values of rela ted parameters, and whether the model can be adapted to predict ozone effects on crops in farmland environment.