Photosynthetic capacity in a central Amazonian rain forest

Abstract

The vertical profile in leaf photosynthetic capacity was investigated in a terra firme rain forest in central Amazonia. Measurements of photosynthesis were made on leaves at five levels in the canopy, and a model was fitted to describe photosynthetic capacity for each level. In addition, vertical profiles of photosynthetic photon flux density, leaf nitrogen concentration and specific leaf area were measured. The derived parameters for maximum rate of electron transport (J(max)) and maximum rate of carboxylation by Rubisco (V(cmax)) increased significantly with canopy height (P < 0.05). The highest J(max) for a single canopy level was measured at the penultimate canopy level (20 m) and was 103.9 &mgr;mol m(-2) s(-1) +/- 24.2 (SE). The highest V(cmax) per canopy height was recorded at the top canopy level (24 m) and was 42.8 +/- 5.9 &mgr;mol m(-2) s(-1). Values of J(max) and V(cmax) at ground level were 35.8 +/- 3.3 and 20.5 +/- 1.3 &mgr;mol m(-2) s(-1), espectively. The increase in photosynthetic capacity with increasing canopy height was strongly correlated with leaf nitrogen concentration when examined on a leaf area basis, but was only weakly correlated on a mass basis. The correlation on an area basis can be largely explained by the concomitant decrease in specific leaf area with increasing height. Apparent daytime leaf respiration, on an area basis, also increased significantly with canopy height (P < 0.05). We conclude that canopy photosynthetic capacity can be represented as an average vertical profile, perturbations of which may be explained by variations in the environmental variables driving photosynthesis.

Relationships Between Tree Height and Carbon Isotope Discrimination

“…10.8). In this analysis, it appears that h dominates the trend in D while irradiance moderates the absolute values, presumably caused by the increased light interception and photosynthetic capacity with increased height and subsequent reduction in p c (Ehleringer et al 1986;Carswell et al 2000;Lloyd et al 2009). While h is clearly a global driver of D, the impact of irradiance on D should vary globally as a function of ecosystem leaf area and subsequent light interception profiles (Campbell and Norman 1998;Parker et al 2002;Koch et al 2004).…”

“…Recycling of isotopically depleted canopy CO 2 should strengthen the gradient of D with h; however, field measurements have shown this effect to be relatively small (Lloyd et al 1996(Lloyd et al , 1997Brooks et al 1997a, b;Buchmann et al 1997a, b). Leaf nitrogen concentration per unit leaf area and photosynthetic capacity sometimes increase with height (and light availability) due to decreased leaf mass per area (e.g., Bond et al 1999;Carswell et al 2000;Barnard and Ryan 2003;Lloyd et al 2009), which could further strengthen the observed relationship of D to h. This has been frequently observed in angiosperms, high leaf area forests, and trees that have not reached their maximum heights. In contrast, studies on particularly tall trees often find that leaf nitrogen per unit mass and photosynthetic capacity do not vary or even decline with h (McDowell et al 2002a;Ambrose et al 2009;Woodruff et al 2009, Nothofagus data from this study).…”

“…10.1 and 10.2), and some environmental variables was originally conceptualized in a seminal paper by Francey and Farquhar (1982). One important size-related environmental change is increased shading within tree crowns (Francey et al 1985;Ehleringer et al 1986;Hanba et al 1997;Carswell et al 2000;Parker et al 2002;Poorter et al 2005;Lloyd et al 2009) which raises p c because A declines via reduced light interception. This change in the light environment occurs within the height profile of individual trees within closed-canopy forests, but does not occur at the tops of canopy-dominant trees or in open-grown trees.…”

Leaf micronutrient concentrations and potential photosynthesis in Ochroma pyramidale established in a degraded land

“…Differences in the C i /C a ratio among plant species have been attributed at least in part to variation in stomatal conductance to CO 2 (Ehleringer & Cerling,1995 (Carswell et al, 2000), indicating that the photosynthetic system of Ochroma was apparently little or not affected by the harsh environmental conditions of this degraded landscape.…”

Características funcionais de folhas de sol e sombra de espécies arbóreas em uma mata de galeria no Distrito Federal, Brasil

“…Dentro dos ambientes fl orestais o acesso à luz é um dos principais fatores limitantes ao crescimento de espécies ar-bóreas (Carswell et al 2000;Felfi li et al 2001;Montgomery & Chazdon 2002). Florestas tropicais caracterizam-se pela presença de um estrato arbóreo desenvolvido que intercepta grande parte da irradiação solar incidente sobre a copa.…”