Development and Structure
Ray, Dustin , Jones, Cynthia S. .
Conduit packing and allometric scaling of tissues in petioles.
Petioles are understudied despite their importance in lamina support, leaf display, and transport of water and photosynthates. While petiole biomechanics has been well studied, the interaction of the vascular tissues and petiole structure has not. The packing rule for woody stems suggests that vessels will fill space that is not necessary for biomechanical support, but this has not been tested in petioles. We measured morphological and anatomical traits for laminas and petioles of 11 species of Pelargonium (L'Her ex. Aiton) to investigate scaling relationships between supporting tissues (fibers), conducting tissues (xylem and phloem), and lamina traits. We found scaling relationships at several different levels of petiole anatomical organization. For individual vascular bundles, phloem tissue area scales positively relative to xylem, but the relationship varies with respect to bundle position (R2 values 0.42 - 0.82; slopes 1.53 – 2.63), suggesting that bundles in different positions vary in their contribution of transport of water relative to photosynthates. Total cross-sectional areas of xylem scaled positively for a given cross-sectional area (R2 = 0.57, slope = 0.86). Because xylem can function in both support and transport, we expected a tradeoff between fiber and xylem area. We found no evidence for such a tradeoff: structural support (cross-sectional area of fibers) did not scale with xylem cross sectional area (R2 = 0.25, slope = 0.82) but both fiber cross-sectional area (R2 = 0.38, slope = 0.89) and xylem-cross sectional area (R2 = 0.51, slope = 0.96) scaled positively with petiole cross-sectional area. Although petiole cross-sectional area is occupied by parenchyma, vessel number per square millimeter scales negatively with vessel diameter (R2 = 0.91, slope = -1.72), as predicted by the packing rule. We built bayesian linear regression models to determine whether petiole, stem and lamina anatomical characters could predict petiole morphometrics. The best model shows that lamina dry mass, petiole length and xylem cross-sectional area are able to predict petiole cross-sectional area. This study is the first to quantify positive allometric scaling of xylem relative to phloem within individual bundles as well as petiole cross sectional area. Several of these scaling relationships have been predicted, but this is the first time they have been quantified.
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1 - University of Connecticut, Ecology and Evolutionary Biology, 75 N Eagleville Road Unit 3043, Storrs, CT, 06269, USA
2 - University Of Connecticut, Department Of Ecology & Evolutionary Biology, 48 Echo Rd., Mansfield Ct., CT, 06250, USA
Presentation Type: Oral Paper
Session: 29, Development and Structure I
Location: 202/Savannah International Trade and Convention Center
Date: Tuesday, August 2nd, 2016
Time: 2:15 PM
Candidate for Awards:Katherine Esau Award,Maynard F. Moseley Award