Leaf photosynthesis and leaf conductance of maize grown hydroponically and in soil under field conditions

This study was undertaken to determine, under field conditions, whether maize (Zea mays L.) plants grown hydroponically and in soil exhibit different stomatal conductance due to nutrient status and rooting media, and whether high photosynthetic rates are associated with high crop yields. Leaf net photosynthesis and leaf conductance to CO₂ were measured in maize between tasseling and crop maturity during the summer of 1986, using a closed gas-exchange system. No difference in net photosynthesis per unit leaf area was found between the soil- and hydroponically-grown plants. There was a linear relationship between net leaf photosynthesis and leaf conductance. On a given day, this relationship was similar in both the hydroponically- and soil-grown plants. The ratio of leaf intercellular CO₂ concentration to ambient CO₂ concentration was similar in both treatments, indicating similar values of water-use efficiency. The net photosynthesis in both treatments was reduced by 40% after two consecutive cool nights, with air temperatures <3°C. Observed leaf photosynthetic rates per unit leaf area were almost identical in both the hydroponically- and soil-grown plants, despite a 25% higher final dry matter yield in the hydroponic treatment. One factor contributing to the increased dry mater production may have been the larger leaf area developed by the hydroponically-grown plants early in the season.