The effect of xylem vessel diameter on potential hydraulic conductivity in different rice stem longitudinal positions

The morphological characteristics of the xylem elements influence water ascent in the plants. Few models determine the physical process of water movement in the vascular system of plants based on the hydraulic architecture. This study aims to determine the anatomical characteristics of the xylem and potential hydraulic conductivity at different positions along the stem of rice (Oryza sativa L.). The xylem vessels characteristics were examined in four internodes using three segments in each internode. The analogy between Ohm's law and Hagen-Poiseuille was used to determine the hydraulic conductivities at three temperatures (18, 25, and 33 degrees C). A successive decrease in the mean vessel diameters from bottom to top stem was observed, with a significant difference between internodes. Between the Internode I and II, there was a 12% reduction in the mean diameter; between the II and III, and III and IV, the decrease was 10 and 28%, respectively. When separated into groups (left and right metaxylem), there was variation in the hydraulically weighted vessels. There was variation in the estimated value of hydraulic conductivity as a function of temperature and along the stem from the base (Internode I) to the plant's top (Internode IV). The decrease in hydraulic conductivity was 41.1 (I-II), 24 (II-III), and 73.4% (III-IV). The estimated value of hydraulic conductivity was increasing with increase in temperature. The variation of the hydraulic conductivity along the useful length of rice allowed a better application of the Hagen-Poiseuille equation.