10027/10417 Douglas J. Lynch Douglas J. Lynch Francesca A. McInerney Francesca A. McInerney Lenny L.R. Kouwenberg Lenny L.R. Kouwenberg Miquel A. Gonzalez-Meler Miquel A. Gonzalez-Meler Plasticity in Bundle Sheath Extensions of Heterobaric Leaves University of Illinois at Chicago 2013 Acer saccharum bulk delta C-13 bundle sheath extension heterobaric Liquidambar styraciflua plasticity water use efficiency 2013-11-07 00:00:00 Journal contribution https://indigo.uic.edu/articles/journal_contribution/Plasticity_in_Bundle_Sheath_Extensions_of_Heterobaric_Leaves/10769954 Premise of the study: Leaf venation is linked to physiological performance, playing a critical role in ecosystem function. Despite the importance of leaf venation, associated bundle sheath extensions (BSEs) remain largely unstudied. Here, we quantify plasticity in the spacing of BSEs over irradiance and precipitation gradients. Because physiological function(s) of BSEs remain uncertain, we additionally explored a link between BSEs and water use efficiency (WUE). Methods: We sampled leaves of heterobaric trees along intracrown irradiance gradients in natural environments and growth chambers and correlated BSE spacing to incident irradiance. Additionally, we sampled leaves along a precipitation gradient and correlated BSE spacing to precipitation and bulk delta C-13, a proxy for intrinsic WUE. BSE spacing was quantified using a novel semiautomatic method on fresh leaf tissue. Key results: With increased irradiance or decreased precipitation, Liquidambar styraciflua decreased BSE spacing, while Acer saccharum showed little variation in BSE spacing. Two additional species, Quercus robur and Platanus occidentalis, decreased BSE spacing with increased irradiance in growth chambers. BSE spacing correlated with bulk delta C-13, a proxy for WUE in L. styraciflua, Q. robur, and P. occidentalis leaves but not in leaves of A. saccharum. Conclusions: We demonstrated that BSE spacing is plastic with respect to irradiance or precipitation and independent from veins, indicating BSE involvement in leaf adaptation to a microenvironment. Plasticity in BSE spacing was correlated with WUE only in some species, not supporting a function in water relations. We discuss a possible link between BSE plasticity and life history, particularly canopy position.