REGULAR PAPER Simulations and observations of patchy stomatal behavior in leaves of Quercus crispula, a cool-temperate deciduous broad-leaved tree species Mai Kamakura • Yoshiko Kosugi • Kanako Muramatsu • Hiroyuki Muraoka Received: 20 June 2011 / Accepted: 23 September 2011 Ó The Botanical Society of Japan and Springer 2011 Abstract We investigated the occurrence of patchy sto- matal behavior in leaves of saplings and a forest canopy tree of Quercus crispula Blume. Through a combination of leaf gas-exchange measurements and numerical simulation, we detected patterns of stomatal closure (either uniform or patchy bimodal) coupled with depression of net assimila- tion rate (A). There was a clear inhibition of A associated with stomatal closure in leaves of Q. crispula during the day, but the magnitude of inhibition varied among days and growing conditions. Comparisons of observed and simu- lated A values for both saplings and the canopy tree iden- tified patterns of stomatal behavior that shifted flexibly between uniform and patchy frequency distributions depending on environmental conditions. Bimodal stomatal closure explained severe depression of A in saplings under conditions of relatively high leaf temperature and vapor pressure deficit. Model simulations of A depression through bimodal stomatal closure were corroborated by direct observations of stomatal aperture distribution using Su- zuki’s Micro-Printing method; these demonstrated that there was a real bimodal frequency distribution of stomatal apertures. Although there was a heterogeneous distribution of stomatal apertures both within and among patches, induction of heterogeneity in intercellular CO 2 concentra- tion among patches, and hence severe depression of A, resulted only from bimodal stomatal closure among pat- ches (rather than within patches). Keywords Bimodal stomatal closure  Leaf gas exchange  Midday depression  Leaf temperature  Vapor pressure deficit Introduction Gas exchange rates between plants and atmosphere are determined by adjustment of photosynthetic capacity and changes in the apertures of stomata on the leaf epidermis. Photosynthesis and transpiration rates in individual leaves vary in response to environmental factors such as light, temperature, water and nutrient supplies. High light, coin- cident with high leaf temperature or water deficit, often causes midday depression of net assimilation rate (A), which is coupled with stomatal closure (Tenhunen et al. 1984; Epron et al. 1995; Valladares and Pearcy 1997; Pathre et al. 1998; Muraoka et al. 2000). Stomatal closure, induced by increased leaf-to-air vapor pressure deficit (VPD) and/or low leaf water potential (Maier-Maercker 1983; Mott and Parkhurst 1991; Brodribb and Holbrook 2004), decreases CO 2 concentration within intercellular spaces (C i ). The reduction of A at midday is the result of both an increase in stomatal limitation and a reduction in the photochemical process (Ishida et al. 1999; Muraoka et al. 2000). Patterns of stomatal closure in canopy leaves of tropical trees may be patchy during severe midday depression (Ishida et al. 1999). Patchy stomatal behavior occurs in M. Kamakura (&)  K. Muramatsu KYOUSEI Science Center for Life and Nature, Nara Women’s University, Kita-uoya Higashimachi, Nara 630-8506, Japan e-mail: mkamakura@cc.nara-wu.ac.jp Y. Kosugi Laboratory of Forest Hydrology, Division of Environmental Science and Technology, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan H. Muraoka Institute for Basin Ecosystem Studies, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan 123 J Plant Res DOI 10.1007/s10265-011-0460-8