Leaf heliotropism in Styrax camporum Pohl from the Brazilian cerrado: distinct gas exchange and leaf structure, but similar leaf temperature and water relations

Abstract

Styrax camporum is a common shrub species from the cerrado regions of São Paulo State, Brazil. Although its leaves do not have a morphologically delimited pulvinus, the apical leaves are oriented parallel to the sun (paraheliotropic leaves), most notably around noon. Horizontal leaves at the base of shoots are oriented perpendicular to the sun's rays (diaheliotropic leaves). The ecophysiological significance of this is not fully understood. We investigated how paraheliotropism influences daily CO 2 assimilation (A) and other gas exchange rates, water relations, leaf temperature (T l ), and how these relate to leaf structure as assessed by anatomical leaf descriptions. Paraheliotropic leaves had greater A and stomatal conductance (g s ), which led to greater transpiration rates (E) during most of the day. However, no categorical data proved that these responses were responsible for the lower T l for vertical leaves, which only occurred at 1100 h and 1600 h. There was no indication that Tl influenced A, E, or g s . However, diaheliotropic leaves did not assimilate less carbon because of a smaller stomatal aperture. Both leaf types had satisfactory stomatal apertures and the same g s range, resulting in similar intercellular CO 2 levels. Paraheliotropic leaves had higher A rates under increased irradiance, suggesting an avoidance of excessive irradiance. Both leaf types had compact spongy parenchyma, representing an increased photosynthetic capacity per unit leaf area. Paraheliotropism in S. camporum does not seem to be related to leaf temperature control, even in the stressful Brazilian cerrado habitat. Key words: Brazilian savanna, ecophysiology, gas exchange, leaf movements, leaf temperature, photosynthesis, Styracaceae Heliotropismo foliar em Styrax camporum Pohl, uma espécie do cerrado brasileiro -padrões distintos de trocas gasosas e estrutura foliar, porém com temperatura foliar e relações hídricas similares: Styrax camporum é uma espécie arbustiva comum dos cerrados do Estado de São Paulo, Brasil. Embora suas folhas não tenham pulvino morfologicamente delimitado, as folhas apicais são orientadas paralelamente à incidência da radiação solar (folhas paraheliotrópicas), especialmente às 1200 h. Folhas horizontais estáticas das partes basais dos ramos são orientadas perpendicularmente aos raios solares (folhas diaheliotrópicas). O significado ecofisiológico do fenômeno não foi ainda completamente elucidado. Investigou-se como o paraheliotropismo influencia a assimilação diária de CO 2 (A) e outras taxas de trocas gasosas, relações hídricas, temperatura foliar (T f ) e suas relações com a estrutura da folha, avaliada por suas descrições anatômicas. Folhas paraheliotrópicas apresentaram maiores A e condutância estomática (g s ), o que levou à maior taxa de transpiração (E) durante grande parte do dia. Todavia, não houve dados categóricos assegurando que estas respostas tenham determinado menor T f para as folhas verticais, que ocorreu apenas às 1100 e 1600 h. Não houve nenhuma indicação de que T f influenciou A, ...

Leaf paraheliotropism in Styrax camporum confers increased light use efficiency and advantageous photosynthetic responses rather than photoprotection

“…For Helianthus annus leaves, direct light reflectance was only slightly higher in the abaxial compared to the adaxial leaf surface, but diffuse light reflectance was significantly higher in the abaxial compared to the adaxial side (Gorton et al, 2010). The stellate pubescence, which covers the abaxial leaf surface and is absent on the adaxial side of S. camporum leaves (Habermann et al, 2008) is, then, responsible for this increased light reflectance. In fact, the effective quantum yield of photosystem II ( PSII) and the electron transport rate (ETR) for both leaf sides of one-year-old S. camporum plants were similar between leaf types, but higher in adaxial compared to abaxial sides (data not shown).…”

“…1c and e). Habermann et al (2008) noted that S. camporum paraheliotropic leaves illuminated on both leaf sides had lower T l and higher E, gs, and A during part of the day compared to diaheliotropic leaves, but neither E nor gs was responsible for the low T l of paraheliotropic leaves, and there was no indication that the low T l explained their high A. When leaves were measured with light interception only on the adaxial leaf sides, no differences in T l were noted between para-and diaheliotropic leaves (Fig.…”

“…Styrax camporum, a non-leguminous species from the cerrado, possesses leaves that are always diaheliotropic as well as other leaves that assume a paraheliotropic position from 10:00 h to 17:00 h (Habermann et al, 2008). Paraheliotropic leaves of this species have higher A and transpiration rates (E) compared to the diaheliotropic leaves, although this high E has a weak relationship with the reduction in leaf temperature (Habermann et al, 2008). This study also demonstrated compact spongy parenchyma in both leaf types, and a rise in A with the increase of irradiance for paraheliotropic leaves.…”

Comparative gas exchange performance during the wet season of three Brazilian Styrax species under habitat conditions of cerrado vegetation types differing in soil water availability and crown density

“…Morphological characteristics of woody species adapted to savannas, such as the Brazilian cerrado, include reduced leaf size, increased leaf and cuticle thickness, a well developed palisade parenchyma and increased sclerophylly (Bieras and Sajo, 2009;Habermann et al, 2008). In the cerrado s.l., there are morphologically similar congeneric species that nevertheless present distinct distribution patterns.…”

Diaheliotropic leaf movement enhances leaf photosynthetic capacity and photosynthetic light and nitrogen use efficiency via optimising nitrogen partitioning among photosynthetic components in cotton (Gossypium hirsutum L.)

“…Nevertheless, paraheliotropism in some species, such as Styrax caporum , is not related to leaf heat avoidance, but serves to increase light use efficiency rather than to increase photoprotection (Habermann et al . , ). Many physiological studies have shown that diaheliotropic leaves have high photosynthesis rates throughout the day, and therefore a high light saturation point and more efficient high light utilisation, because of the relatively constant high PAR interception (Ehleringer & Forseth ; Sailaja & Das ; Zhu et al .…”