|Pachepsky, Ludmilla - DUKE UNIVERSITY|
|Lu Zhen, Min - DUKE UNIVERSITY|
Submitted to: Biotronics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 31, 2000
Publication Date: N/A
Interpretive Summary: Opening and closing stomata is an important mechanism of plant photosynthesis, transpiration regulation, and leaf temperature control. Some plants are hypo stomatous, that is, have stomata only at one side of leaf, others, cotton among them, are amphystomatous. Amphystomatous means they have stomata at both sides of their leaves. These plants have an additional degree of freedom in regulating their gas exchange because they can open and close stomata at different sides of leaves. Such behavior was observed in cotton. The objective of this study was to quantify the advantages for Pima cotton plants which may arise from different stomata closure regulation at two leaf sides. Photographs of leaf surfaces and leaf cross-sections of eight cotton varieties and image analysis software were used to measure stomatal densities and internal leaf space available for gas movement. These data were entered into the 2DLEAF, model of leaf gas exchange, to simulate leaf gas exchange, which would occur in different modes of stomatal closure at two leaf sides. Due to different stomatal density on two leaf sides, transpiration is more sensitive to changes in stomata's aperture on the abaxial, which is the high stoma density side of the leaf. The other side of leaf plays an important role when the stomata are wide open. The effect of the stomata closures difference on transpiration was stronger when the stomatal closures were low. Therefore, as temperature rises, cotton plants may use the differences in stomatal closure to improve leaf temperature regimes.
Technical Abstract: Leaf photosynthesis and transpiration of eight genotypes of Pima cotton (Gossypium barbadense L.) were measured in the field at the Maricopa Agricultural Center in August 1994. Microphotographs of leaf cross-section and of the abaxial and adaxial surfaces of leaves, taken from the same field, were scanned and analyzed with the image analysis software. Selection process, as reflected in the sequence of the studied Pima cotton genotypes, did not significantly affect the leaf gas exchange or the leaf anatomical characteristics. Only the oldest variety, P32, had the parameters significantly different from those of the more recent lines. The data were used to parameterize and validate the 2DLEAF model developed earlier for two-dimensional modeling of leaf gas exchange and accounting for leaf anatomy. The model was used to study the effect on transpiration of the stomatal regulation on the abaxial and adaxial. The hypothesis about possible differences presented in several earlier studies with a number of species was confirmed in this study. At low stomatal apertures, the mode of stomatal closure on different leaf sides affects the transpiration rates more strongly than at higher values of stomatal openness. Transpiration rates are more sensitive to the abaxial stomatal closure, but the adaxial stomata play a more important role when the stomata are widely open.