Leaf Gas Exchange of Eastern Redbud (Cercis canadensis L.) Grown Under Sun and Shade

Abstract

Abstract Leaf physiology of eastern redbud (Cercis canadensis L.) was assessed under natural photoperiod when grown in 100% sun or under polyethylene shade with a light transmittance of 69%, 47%, or 29% sun. Net CO2 assimilation rate (A) was similar under 100%, 69%, and 47% sun; A was reduced under 29% sun. Adaptations to shade included a near perpendicular leaf orientation to the sun, reduction in specific leaf weight (SLW), and a decreased chlorophyll a: chlorophyll b ratio. Conversely, eastern redbud adapted to 100% sun by manifesting an increased SLW and a vertical orientation of leaves that curled inward toward the midrib. Light response curves were similar for sun- and shade-acclimatized plants. When all data were analyzed collectively, A was most closely related to photosynthetic photon flux (PPF) (R2 = 0.52), whereas stomatal conductance to water vapor (gs) was primarily influenced by vapor pressure deficit (VPD) (R2 = 0.75). Hence, A and gs were not well correlated (R2 = 0.41). The lack of strong coupling between A and gs allowed the stomates to remain open under low PPF, resulting in an elevated intercellular CO2 concentration. Thus, A was stimulated above what might have normally occurred under low PPF.