BEHAVIOR OF MAIZE STEM DIAMETER DURING DRYING CYCLES - COMPARISON OF 2 METHODS FOR DETECTING WATER-STRESS

Changes in stem diameter are frequently used to assess plant water status. We have compared two ways of data processing, analyzing either the changes in daily stem contraction (the most commonly used method) or the changes in daily maximum stem diameter (DMSD). Changes in stem diameter of adult maize (Zea mays L.) plants were measured during drying cycles either in the field or in a pot experiment, together with predawn leaf water potential, noon-time stomatal conductance, noon-time leaf water potential, and fraction of soil transpirable water. Close relationships, common for field and pot experiments, were observed between changes in DMSD and predawn leaf water potential (r(2) = 0.91), and noon-time stomatal conductance (r(2) = 0.81). Relationships also existed between DMSD and the fraction of soil transpirable water (r(2) = 0.84 and 0.87 in the field and pot experiments, respectively). In contrast, the daily stem contraction showed complex and loose relationships with soil and plant water status, and with stomatal conductance. This is consistent with the facts that (i) maize day time plant water status undergoes relatively little change during drying cycles, and (ii) stomatal conductance is linked to the soil water status, and is therefore correlated to measurements characterizing night-time plant water status such as DMSD or predawn leaf water potential. A practical consequence would be that changes in DMSD should be used rather than daily stem contraction for characterizing plant water status of maize, or for triggering the beginning of irrigation in automatic systems.