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 sta tus. We have compared two ways of data processing, analyzing either th e changes in daily stem contraction (the most commonly used method) or the changes in daily maximum stem diameter (DMSD). Changes in stem di ameter of adult maize (Zea mays L.) plants were measured during drying cycles either in the field or in a pot experiment, together with pred awn leaf water potential, noon-time stomatal conductance, noon-time le af water potential, and fraction of soil transpirable water. Close rel ationships, common for field and pot experiments, were observed betwee n changes in DMSD and predawn leaf water potential (r(2) = 0.91), and noon-time stomatal conductance (r(2) = 0.81). Relationships also exist ed between DMSD and the fraction of soil transpirable water (r(2) = 0. 84 and 0.87 in the field and pot experiments, respectively). In contra st, 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 statu s undergoes relatively little change during drying cycles, and (ii) st omatal conductance is linked to the soil water status, and is therefor e correlated to measurements characterizing night-time plant water sta tus such as DMSD or predawn leaf water potential. A practical conseque nce would be that changes in DMSD should be used rather than daily ste m contraction for characterizing plant water status of maize, or for t riggering the beginning of irrigation in automatic systems.