Seasonal variation in the maximum rate of leaf gas exchange of canopy and understory tree species in an Amazonian semi-deciduous forest

Abstract

Leaf gas exchange, water potential, and specific leaf area of two tropical semi-deciduous tree species, Brosimum lactescens S. Moore and Tovomita schomburgkii Planch & Triana, were quantified to establish how these properties were affected by seasonal variations in rainfall and leaf canopy position. The study was conducted at a site near Sinop Mato Grosso, Brazil, which is located within the ecotone of savanna and tropical rain forest. Both species exhibited significant declines in leaf water potential (Ψ L ), specific leaf area, area-and mass-based light saturated photosynthesis and dark respiration, and maximum stomatal conductance during the dry-season, suggesting that leaf structural properties and gas exchange are significantly altered by drought that develops during the 4-month dry season. Internal leaf CO 2 concentrations (C i ) were consistently lower during the dry season suggesting that the decline in maximum photosynthesis was due in part to a decline in stomatal conductance. However, seasonal variations in leaf gas exchange were larger for upper-canopy leaves, indicating an important interaction between drought stress and canopy position. The seasonal variation in leaf gas exchange and morphology was presumably due to a combination of drought stress and leaf lifespan. The results of this study suggest that drought has important implications for the leaf physiology and morphology of semi-deciduous Amazonian forest trees.

Seasonal Patterns of Evapotranspiration for a Vochysia divergens Forest in the Brazilian Pantanal

“…Similar results were observed in humid subtropical Everglade's wetlands (Shoemaker and Sumner 2006). Thus, even with ample surface water availability and consistently high LAI there was significant resistance to water vapor exchange from stomatal closure (McWilliam et al 1996;Sa et al 1996;Vourlitis et al 2008;Sendall et al 2009), hydraulic conductivity (Meinzer et al 1993;Eamus 1999), and canopy structure (Jarvis and McNaugton 1986). This response has been described in other tropical forests (Meinzer et al 1993;Vourlitis et al 2005) and has likewise been attributed to stomatal closure caused by high evaporative demand.…”

Temporal patterns of net CO2exchange for a tropical semideciduous forest of the southern Amazon Basin

“…The quantum yield ( a ′) increased as a function of precipitation and declined as a function of average monthly PAR. The a ′ response to rainfall has been observed in studies of leaf photosynthesis [ Miranda et al , 2005; Sendall et al , 2009] and NEE [ Vourlitis et al , 2001, 2004, 2005; Priante‐Filho et al , 2004], highlighting the importance of rainfall and water availability on photosynthetic light‐use efficiency. The physiological basis for the negative relationship between a ′ and PAR is less clear because there is little evidence that light‐use efficiency is affected by the overall light environment [ Boardman , 1977].…”

“…Seasonal and interannual drought has long been recognized as a potentially important control on the productivity and NEE of tropical ecosystems [ Medina and Klinge , 1983; Condit et al , 1996; Nepstad et al , 2002; Saleska et al , 2003; Goulden et al , 2004; Hutyra et al , 2007; Vourlitis et al , 2004, 2005; Vourlitis and da Rocha , 2010]. Seasonal drought has been shown to limit rates of leaf gas exchange [ Miranda et al , 2005; Sendall et al , 2009], soil and ecosystem respiration [ Meir et al , 1996; Sotta et al , 2004; Valentini et al , 2008], and net [ Zhao and Running , 2010] and gross primary production [ Saleska et al , 2003; Vourlitis et al , 2004], and the annual amplitude of NEE is strongly influenced by annual precipitation and dry season length [ Vourlitis et al , 2005; Vourlitis and da Rocha , 2010]. Recently, however, studies relying on satellite‐based remote sensing suggest that seasonal drought can lead to a “green‐up” during the dry season and an increase in productivity [ Saleska et al , 2007], while others find no evidence of a dry season green‐up, and that overall, seasonal drought causes a decline in productivity [ Samanta et al , 2010; Zhao and Running , 2010].…”

Modelling Gross Primary Production of Tropical Forest by Remote Sensing

“…The importance of precipitation for the LUE has been well documented and observed by Sendall et al (2009) and Vourlitis et al (2011) to study the net photosynthetic rate and net exchange system in the same area of study. The negative relationship between PAR and LUE is not conclusive, as there is little evidence that the LUE is affected by radiation (BOARDMAN, 1977).…”

“…The GPP was 21% higher during the wet season (Table 1). The strong direct relationship between water availability, rainfall, leaf water potential and photosynthesis have been well documented in the tropical semi-deciduous forests (MIRANDA et al, 2005;SENDALL et al, 2009;BIUDES et al, 2014a). …”