Leaf optical properties as affected by shade in saplings of six tropical tree species differing in successional status

Abstract

Tree species differing in successional status may present different responses to shade. Adjustments at leaf level may affect their optical properties, leading to changes in PAR (photosynthetically active radiation) absorbance. The aim of this study was to evaluate leaf optical properties as affected by understory shade in saplings of six tropical tree species differing in successional status and degree of shade tolerance. Chlorophyll content and specific leaf area (SLA) were also evaluated. The effects of shade on leaf optical properties and chlorophyll content differed among the studied species, whereas increased SLA was a common response for all species, reflecting the occurrence of thinner leaves under shade. The three studied shade-tolerant species -Esenbeckia leiocarpa, Myroxylon peruiferum and Hymenaea courbarilpresented a greater PAR absorbance under shade. The response of the shade-intolerant species was varied. While Schizolobium parahyba also showed a greater PAR absorbance under shade, Chorisia speciosa did not alter its spectral properties and Cecropia pachystachya presented an opposite pattern, with smaller absorbance under shade. Increases in leaf chlorophyll content were significant in the shade-tolerant species, whereas they were absent or of small magnitude in the shade-intolerant ones. Although the shade-induced decrease of leaf reflectance was the only response that safely discriminated tolerant from intolerant species, the adjustments in leaf chlorophyll content and optical properties were more consistent for the tolerant species.Key words: Chlorophyll, leaf absorbance, shade tolerance, specific leaf area, successional species.Alterações das propriedades ópticas de folhas em resposta a sombreamento em plantas jovens de seis espécies arbóreas tropicais pertencentes a diferentes estádios de sucessão: Espécies arbóreas tropicais pertencentes a diferentes estádios de sucessão podem apresentar diferentes respostas ao sombreamento. Ajustes apresentados ao nível das folhas podem afetar as propriedades ópticas, levando a alterações na absorbância da radiação fotossinteticamente ativa (RAF). O objetivo deste trabalho foi avaliar alterações das propriedades ópticas foliares em resposta ao sombreamento natural em plantas jovens de seis espécies arbóreas tropicais pertencentes a diferentes estádios de sucessão e com diferente grau de tolerância à sombra. Conteúdo de clorofila e área foliar específica (AFE) também foram avaliados. Os efeitos do sombreamento sobre as propriedades ópticas foliares e conteúdo de clorofila diferiram entre as espécies estudadas, ao passo que o aumento da AFE foi uma resposta comum, refletindo a ocorrência de folhas mais finas. As três espécies tolerantes à sombra -Esenbeckia leiocarpa, Myroxylon peruiferum e Hymenaea courbaril -apresentaram uma maior absorbância da RAF sob sombreamento. A resposta das espécies intolerantes à sombra foi variada. Enquanto Schizolobium parahyba também apresentou maior absorbância da RAF sob sombreamento, Chorisia speciosa não alterou suas proprie...

Leaf optical properties of two liana species Canavalia parviflora Benth. and Gouania virgata Reissk in different light conditions

“…In seasonal forests, with a well-defined dry season, a reduced absorptance value would benefit to liana species that predominate in marginal environments, such as the edge of forests where they are exposed to high light, scarcity of water and high vapour pressure deficits. Souza & Válio (2003b) also found mean absorptance values of 76% under full sun for tree species differing in successional status in the same area of this study. In this case, the slightly higher absorptance values for lianas compared to species investigated by Souza & Válio (2003b) could be, with other physiological attributes, a support for their competitive growth pattern in clearings and edge gaps.…”

“…Souza & Válio (2003b) also found mean absorptance values of 76% under full sun for tree species differing in successional status in the same area of this study. In this case, the slightly higher absorptance values for lianas compared to species investigated by Souza & Válio (2003b) could be, with other physiological attributes, a support for their competitive growth pattern in clearings and edge gaps. Futher studies of leaf physiology under contrasting light regimes are necessary to clarify possible differences between liana and tree species.…”

“…Structures like wax or G. virgata under 1.5% PFD) (data not shown). Moreover, C. parviflora also showed an increase in absorptance after 700 nm under 1.5% PFD, as mentioned earlier by Lee & Graham (1986), Poorter et al (1995) and Souza & Válio (2003b). Considering that understory environment is more enriched with far-red wavelengths, the use of quanta in the 700-750 range may be of great value for overall carbon gain in this environment (Lee & Graham 1986).…”

“…Although some studies stated that no pronounced differences were observed in leaf optical properties between sun and shade species, or between exposed and shaded leaves of a particular species (Lee & Graham 1986, Knapp & Carter 1998, Cao 2000, other works showed that, greater adjustments on leaf characteristics occurred, in shade tolerant species, which might increase light absorptance efficiency under limited light (Poorter et al 1995, Souza & Válio 2003b.…”

“…For instance, adjustments to low irradiance may lead to alterations in leaf thickness (increase in specific leaf area), higher chlorophyll and carotenoid content per unit weight, and yet, shade leaves may be relatively more enriched in chlorophyll b with relation to chlorophyll a, resulting in low chlorophyll a/b ratio compared to sun leaves (Evans & Poorter 2001, Souza & Válio 2003b). All these changes should affect the leaf optical properties (Lee et al 1990, Vogelmann 1993).…”