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Title: PIMA cotton leaf transpiration analysis using the wallmodel that accounts for liquid water movement

Author
item Pachepsky, Ludmila
item FERREYRA, RAFAEL
item Sadeghi, Ali

Submitted to: International Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2009
Publication Date: 7/9/2009
Citation: Pachepsky, L., Ferreyra, R.A., Sadeghi, A.M. 2009. PIMA cotton leaf transpiration analysis using the wallmodel that accounts for liquid water movement. International Journal of Plant Science. 23(4):1-10.

Interpretive Summary: Leaf transpiration is a mechanism that mediates water flow in plants. Previous transpiration models were primarily based on water evaporation from leaf interval surfaces and water vapor escaping through the leaf stomata. This study was specifically designed to evaluate a new model, called “WALL MODEL” that directly relate leaf transpiration to liquid water movement inside the leaf and to cuticular transpiration. Water movement is assumed to move from the vein ending within the plane leaves towards the upper and lower leaf surfaces. We used Pima cotton (Gossypium barbadense L.) for validating model parameters. Pima cotton is normally grown in the hottest areas of the Southwestern United States and was particularly bred for the irrigated cotton production. Calculations with the WALL model showed that cuticular transpiration can be quite high and plays a significant role in protection leaves from overheating. The cuticle occupies about 96-99.5% of the leaf area, far more than the stomata do used in the conventional type models.

Technical Abstract: Leaf transpiration of eight genotypes of Pima cotton was measured in the field of the Maricopa Agricultural Center in August 1994 at the University of Arizona. Photomicrographs of leaf cross-sections and of the leaf surfaces were scanned and analyzed with the image analysis software. The data were used to parameterize the WALL model that was developed primarily to study the leaf transpiration with a special emphasis to liquid water movement inside the leaf. The transpiration stream in the model is assumed to go from vein endings in two directions, towards the upper and lower leaf surfaces. These fluxes presented as two parallel currents driven by the water vapor concentration difference between the atmosphere and the open surface of the vein endings and on the cells’ surfaces. Model simulations were performed: i) to estimate quantitatively the contribution of the cuticular transpiration to the total amount of leaf transpiration stream; ii) to evaluate the role of the mesophyll cell walls’ surfaces in the water transfer inside the leaf; and iii) to calculate the dependence of transpiration and its components on temperature. Simulation results showed: 1) the critical role of the cuticular transpiration as a leaf cooling mechanism; and 2) that the cell wall properties can affect water film characteristics that also affect the transpiration course.