Simulation of the effects of carbon dioxide, climate change, and controlled environments on wheat growth and development

Rising atmospheric CO{dollar}sb2{dollar} concentration and future climate change will affect wheat production worldwide. This thesis focuses on modeling the response of a wheat crop to elevated CO{dollar}sb2{dollar}, as modulated by temperature, water and nutrient supply. An existing field-tested model for wheat growth and development, CERES-Wheat, is modified by a routine that simulates canopy light absorption and photosynthesis from simplified leaf dynamics. Simulations of field conditions give results in agreement with previous experimental studies: The yield response to CO{dollar}sb2{dollar} is limited by nitrogen supply; and water-stressed canopies respond more strongly to CO{dollar}sb2{dollar} than do irrigated ones. A positive feedback between simulated root water uptake and root biomass accumulation is shown to enhance the relative response of water-stressed canopies, in addition to the effects of stomatal closure. Simulations of field conditions further indicate that the beneficial effects of CO{dollar}sb2{dollar} fertilization might be counterbalanced by increasing temperatures. Data on canopy light interception, photosynthesis and respiration, root growth and root respiration, relative to wheat grown in controlled hydroponic environments under both ambient (330 ppm) and elevated (1200 ppm) CO{dollar}sb2{dollar} concentration are used for further model testing and development. It is shown that modeling the ratio of diffuse-to-direct light above the canopy is necessary in order to use the field-tested model for simulations in controlled environments. Refinements are made to model calculations of carbon partitioning, root respiration, leaf expansion rates, and leaf senescence. With these modifications, the new photosynthetic routine is shown to reproduce closely the observed growth chamber data.