Agricultural and Forest Meteorology 158–159 (2012) 13–20 Contents lists available at SciVerse ScienceDirect Agricultural and Forest Meteorology jou rn al h om epa g e: www.elsevier.com/locate/agrformet Diversity in nighttime transpiration behavior of woody species of the Atlantic Rain Forest, Brazil Bruno H.P. Rosado a,∗ , Rafael S. Oliveira a , Carlos A. Joly a , Marcos P.M. Aidar b , Stephen S.O. Burgess c,d a Departamento de Biologia Vegetal, IB, Universidade Estadual de Campinas, Campinas, SP, Brazil b Sec ¸ ão de Fisiologia e Bioquímica de Plantas, Instituto de Botânica, São Paulo, SP, Brazil c Faculty of Agriculture, Food and Natural Resources, The University of Sydney, Sydney, Australia d School of Plant Biology, The University of Western Australia, Perth, Australia a r t i c l e i n f o Article history: Received 30 April 2011 Received in revised form 18 January 2012 Accepted 3 February 2012 Keywords: Cooling effect Xylem refilling Sensible heat flux Latent heat flux Sap flow Micrometeorology a b s t r a c t Nighttime transpiration (NT) has been documented in many plant species but we do not yet have a thorough understanding of the abiotic and biotic controls of this phenomenon. In this study we examined interspecific variation in NT behaviors in plants with distinct crown exposures (CE) and occurring at lowland (100 m) and montane forests (1000 m) in the Brazilian Atlantic rainforest to answer the following questions: are there different NT behaviors in plants subjected to distinct conditions associated with degree of CE and/or altitude? Are there higher rates of NT relative to daily maximum values at the montane forest due to higher vapor pressure deficit (VPD)? Taking into account that low VPD should generally produce low relative NT fluxes, should we expect that understory species in both altitudes will have quite uniform low relative rates of NT in comparison to overstory species owing to the buffered nature of within-canopy microclimate? NT did show differences between altitude and species. Of most significance was a prominent non-linear relationship between the NT and VPD, observed at the montane site. This non- linearity is in contrast to most previously published NT kinetics and suggests stomatal and/or leaf energy balance controls on NT. Our findings raise a new perspective concerning thermodynamic contributions to non-linear NT kinetics and some possible reasons for this interesting behavior are discussed. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Transpiration by plants follows a force–flux relationship that is shaped by the ability of a plant’s transport system to conduct water. Plants can modify their hydraulic conductivity through- out the entire transport system and perhaps the strongest and most dynamic control is that of stomatal aperture which affects conductance to water vapor: understanding stomatal behavior in response to environmental conditions is thus key to understand- ing variation on plant water fluxes (Cowan and Farquhar, 1977; Jones and Sutherland, 1991; Cruiziat et al., 2002). A commonly known relationship between transpiration and vapor pressure deficit (VPD) shows a non-linear saturating response of daytime transpiration to VPD because of decreases in stomatal conductance in response to a drying atmosphere (Jones and Sutherland, 1991; Cruiziat et al., 2002). While daytime transpiration dynamics are ∗ Corresponding author. Present address: Instituto de Pesquisas Jardim Botânico do Rio de Janeiro, Diretoria de Pesquisas, 22460-030 Rio de Janeiro, RJ, Brazil. Tel.: +55 0 21 32042125; fax: +55 0 21 2259 5041. E-mail address: brunorosado@gmail.com (B.H.P. Rosado). quite well studied, nighttime transpiration (NT) has only recently become an important research subject. NT has been described for quite a few plant species from contrasting environments (Donovan et al., 2001; Dawson et al., 2007; Snyder et al., 2008; Christman et al., 2008; Novick et al., 2009) and while generally lower in magnitude relative to daytime transpiration, it is none-the-less significant enough for potential impacts on whole-plant water relations and ecosystem hydrology (Dawson et al., 2007; Wood et al., 2008). Functional consequences of NT include pre-dawn disequilibrium, increases in oxygen supply (Daley and Phillips, 2006) and facilitation of bulk flow of water to the roots overnight which may promote nutrient uptake (Donovan et al., 2001; Snyder et al., 2003). Although little is known about the controls of NT, a strongly linear positive relationship between sapflow and VPD has been documented in several ecosystems, sug- gesting that VPD is the most important environmental driving force for nocturnal water loss and that the crown conductivity is constant (Fisher et al., 2007; Dawson et al., 2007). In tropical forests, small-scale changes in abiotic factors such as VPD, air temperature and solar radiation are common due to the large heterogeneity of canopy structure, topography and wind patterns (Motzer, 2005). Thus, even in short horizontal and altitudinal distances, plant species may be subjected to high 0168-1923/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.agrformet.2012.02.002