Effect of Carbon Dioxide, Osmotic Potential of Nutrient Solution, and Light Intensity on Transpiration and Resistance to Flow of Water in Pepper Plants

The rate of transpiration, temperature of the leaves, and relative water content of leaves of pepper plants were measured in a small chamber in which the temperature, relative humidity, and carbon dioxide concentration of recirculated air were controlled and measured. The data reported were obtained by noting the response of pepper plants to all combinations of the following treatments: high light, 1.5 x 10(6) ergs per square centimeter per second; low light, 3.0 x 10(4) ergs per square centimeter per second; three levels of CO(2): 50, 268, and 730 parts per million; nutrient solution osmotic potentials of -0.5, -5.0, -7.5, and -9.5 bars.The rate of transpiration of pepper plants was reduced by a decrease in osmotic potential of the nutrient solution, an increase in CO(2) concentration in the ambient air, and a decrease in light intensity. The response, as measured by transpiration, to the three variables, light, CO(2), and osmotic potential indicated that each variable influenced a different and independent mechanism. A change in a single variable produced essentially the same percentage change at all levels of the other variables. The rate of movement of water from roots to leaves was in response to water potential gradient and not the actual potential in the leaves.The resistance to flow of water through the plants (R) was estimated by dividing the difference between the water potentials of the solution and the leaves by the rate of transpiration. The data indicated an increase in R as the rate of transpiration decreased. The type and size of errors encountered in the estimation of R and location of R within the plant are discussed.