Contrasting physiological effects of tropical leaf vein network scale in response to damage

Luiza Maria T. Aparecido, School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA, Miguel Duarte and Martha Ryan, School of Life Sciences, Arizona State University, Tempe, AZ, Emily Guevara Heredia, Rafael E. Cárdenas and Renato Valencia, Escuela de Ciencias Biológicas, Pontificia Universidad Católica del Ecuador, Quito, Ecuador, Mark Fricker, Department of Plant Sciences, University of Oxford, Oxford, United Kingdom, Benjamin Blonder, ESPM, University of California Berkeley, Berkeley, CA

Background/Question/Methods
Mechanical damage and herbivory can result in reduced leaf productivity and water transport. Vein network architecture may influence these responses, as veins of different connectivities and sizes may provide alternate flow pathways. Our study investigated whether 1) vein damage of different types affected gas exchange rates in tropical tree species, and 2) whether different venation network properties for large or small veins would influence the sign and strength of post-damage responses. We collected physiological measurements (photosynthesis (An), transpiration (Et), and stomatal conductance (gs)) and whole-leaf samples for leaf venation characterization from 14 mature tropical tree species at the Yasuni National Park in Ecuador. Measurements were taken before (control) and after damage to major or secondary veins. Additional leaf traits (e.g., leaf thickness, leaf area, specific leaf area, shearing and tearing force) were collected during previous campaigns in the same study site by collaborators.
Results/Conclusions
Physiological responses to vein damage varied widely among species and treatments. Major vein damage showed the strongest An rate decline (-30 ± 25%), while secondary vein damage only slightly affected An (-6 ± 17%). Similar trends were observed for Et and gs, but not as strongly as An. Among leaf traits analyzed, only thickness was significantly correlated to An variation after damage (r2=0.20). Strong An decline was observed across species with higher density of small veins, after both major and secondary vein damage. Less An decline was observed regardless of the density of larger veins, for both major and secondary vein damage. The effect of vein density of small veins was greatest after damage to the major veins.
These findings suggest that damage to major veins most negatively impacts gas exchange in species with more minor veins, and that damage to secondary veins most negatively impacts species with fewer secondary veins. Thus there are tradeoffs between resource supply under undamaged conditions and ability to maintain resource supply after damage. Selection for different network architectures with different densities of small and large veins may reflect this tradeoff, though they do not seem to relate to mechanical functions of venation.