Influence of shoot inclination on irradiance and morphophysiological leaf traits along shoots in cerrado trees with distinct leaf deciduousness

Abstract

This study investigated the relationship among shoot inclination, irradiance and morphophysiological traits of basal (BL) and distal (DL) leaves in six cerrado trees with distinct leaf deciduousness. Deciduous species showed plagiotropic shoots (44º) and larger leaf area than semideciduous and evergreen species, which showed orthotropic shoots (56º and 63º, respectively). Despite larger leaf area, irradiance at shoot base in deciduous was around 85% in relation to full irradiance, while in semideciduous and evergreen only 23% of irradiance reached on BL. Likewise, maximum net photosynthesis (P nmax ) was similar between BL and DL in deciduous. Contrastingly, semideciduous and evergreen showed significant decreasing of P nmax in BL. Plagiotropic shoots of deciduous allow similar irradiance along shoots, resulting in similar P nmax along shoot. On the other hand, orthotropic shoots of semideciduous and evergreen resulted in shading and decreasing of P nmax on BL. However, considering BL and DL together, there was not significant difference of leaf-life-span or P nmax among deciduous, semideciduous and evergreen. Therefore, shoot inclination and shading among leaves on same shoot should be significant influencing leaf morphophysiological traits along shoots in cerrado trees. On the other hand, similar leaf-life-span among phenological groups resulted in absence of P nmax differences when BL and DL were considered together.Key words: Leaf-life-span, maximum net photosynthesis, orthotropic, self-shading, plagiotropic. resumoAs relações entre a inclinação do ramo, irradiância e as características morfofisiológicas de folhas basais (FB) e distais (FD) foram investigadas em seis espécies arbóreas de Cerrado com distintas fenologias foliares. Espécies decíduas apresentaram ramos plagiotrópicos (44º) e maior área foliar do que espécies semidecíduas e sempreverdes com ramos ortotrópicos (56º e 63º, respectivamente). Nas espécies decíduas a irradiância solar foi de 85% na base do ramo, mas nas espécies semidecíduas e sempreverdes menos de 23% da irradiância incidiu nas FB. As decíduas apresentaram fotossíntese líquida máxima (P nmax ) equivalente entre FB e FD, porém, nas semidecíduas e sempreverdes ocorreu uma diminuição significativa de P nmax nas FB. Os ramos plagiotrópicos das decíduas permitiram uma equivalente irradiância solar e similar P nmax ao longo do ramo. De forma contrastante, os ramos ortotrópicos das semidecíduas e sempreverdes resultaram em intenso sombreamento e diminuição de P nmax nas FB. Considerando conjuntamente FB e FD, não houve um gradiente significativo dos valores do tempo de vida da folha (TVF) ou P nmax entre decíduas, semidecíduas e sempreverdes. A inclinação do ramo e o sombreamento correspondente entre as folhas são importantes fatores para a determinação de P nmax ao longo dos ramos nas espécies arbóreas de Cerrado. Por outro lado, quando FB e FD foram consideradas conjuntamente não houve diferença de P nmax entre os grupos fenológicos estudados devido à similaridade do TVF.Palavras...

Relationships between crown architecture and available irradiance in two cerrado species with different leaf phenologies

“…The evergreen species, H. stigonocarpa, had orthotropic shoots and higher leaf areas per shoot (LA), factors that increase self-shading along the same shoot (Souza et al 2009a); greater leaf areas result in intense shading along shoots, but the greater leaf areas allow the upper leaves to intercept more solar radiation for photosynthetic purposes. Additionally, the alternate distichous phyllotaxis of evergreen species increases the shading of their basal leaves by distal leaves along the same shoot as they are aligned along the same plane.…”

“…branching patterns) result in leaves having different insertions onto their supporting shoots (Souza et al 2009a, b) that have direct implications for light interception (Press 1999, Faslter & Westoby 2003 and will therefore infl uence biomass distribution to the leaves and shoots. In general, species that demonstrate synchronous leaf fl ushing on plagiotropic shoots avoid self-shading and irradiance is more or less evenly distributed along the shoots (Kikuzawa et al 1996, Souza et al 2009a. Species with continuous leaf production, however, tend to have orthotropic shoots whose basal leaves receive less irradiance than the younger leaves at the shoot apex (Kikuzawa 2003, Souza et al 2009a).…”

“…In general, species that demonstrate synchronous leaf fl ushing on plagiotropic shoots avoid self-shading and irradiance is more or less evenly distributed along the shoots (Kikuzawa et al 1996, Souza et al 2009a. Species with continuous leaf production, however, tend to have orthotropic shoots whose basal leaves receive less irradiance than the younger leaves at the shoot apex (Kikuzawa 2003, Souza et al 2009a). According to Souza et al (2009a), there is little data available concerning how leaf positions along the shoot or shoot inclination affect the incidence of light on the leaves, despite the wide variations in irradiance intensity within different cerrado phytophysiognomies.…”

“…Species with continuous leaf production, however, tend to have orthotropic shoots whose basal leaves receive less irradiance than the younger leaves at the shoot apex (Kikuzawa 2003, Souza et al 2009a). According to Souza et al (2009a), there is little data available concerning how leaf positions along the shoot or shoot inclination affect the incidence of light on the leaves, despite the wide variations in irradiance intensity within different cerrado phytophysiognomies. According to Werner et al (2001), light absorption is higher among leaves that are positioned perpendicular to the sun, while vertical orientations will reduce light interception rates.…”

“…Shading within the crowns of cerrado trees is infl uenced by the inclination of the branches (Souza et al 2009a) and by patterns of biomass allocations between leaves and shoots (Souza et al 2009b). In species with slanting shoots (where light incidence is equally distributed among all the leaves along the shoot), more biomass can be allocated to leaves than to shoots without signifi cant increases in self-shading (Souza et al 2009b).…”