Photosynthetic rate, stomatal resistance and leaf water potential in cotton (Gossypium hirsutum L.) as affected by soil moisture and irradiance

The effects of moisture stress on leaf water potential, photosynthetic rate (PN) and stomatal resistance (rs) of cotton, Gossypium hirsutum, were studied under field conditions. Sprinkler irrigation trials were conduced using the single source line technique. Rs increased and PN decreased as a result of moisture stress, more than in a concurrent drip irrigation experiment. Rs was only slightly affected by irradiance when the plants were subjected to moisture stress, but it decreased in response to an increase in irradiance (I) in the well irrigated plants. A linear relationship between leaf water potential and rs and between leaf water potential and PN, was found in both experiments at low I, whereas exponential relationship was found at high I. Even though high values of rs were recorded under the extreme moisture stresses of both experiments, internal CO2 concentration increased during the day, indicating that non-stomatal factors (such as mesophyll resistance) are the main factors limiting the photosynthetic process.