Objective: Determine endogenous and environmental factors limiting plant responses to elevated carbon dioxide. Determine effects of reduced respiration at elevated carbon dioxide levels. Identify fundamental mechanisms contributing to acclimation of photosynthesis to elevated carbon dioxide. Identify mechanisms controlling genetic variation in stimulation of yield and other responses of plants to elevated carbon dioxide. Determine how rising atmospheric carbon dioxide alters weed-crop interactions.

Approach: Experiments will be performed in controlled environment chambers, air conditioned glasshouses and field plots at ambient and elevated CO₂.
1) Photosynthetic acclimation and carbohydrate and nitrogen partitioning will be measured as functions of

developmental stage, nutrient status, light and temperature.

2) Stomatal conductance, transpiration, water potential, gas exchange and growth responses to drying will be compared at different CO₂ concentrations.

3) Short-term responses of respiration to elevated CO₂ will be determined for different conditions and related to responses of growth to high and low CO₂ dioxide during the dark period.

4) Diverse locally adapted cultivars of soybean will be examined in detail in field plots.

5) Crops will be grown with and without competition from weeds at different carbon dioxide concentrations in field plots. Crop-weed competition will be examined under conventional and more sustainable management systems.