Acclimation of leaves to contrasting irradiance in juvenile trees differing in shade tolerance

Abstract

Leaves developing in different irradiances undergo structural and functional acclimation, although the extent of trait plasticity is species specific. We tested the hypothesis that irradiance-induced plasticity of photosynthetic and anatomical traits is lower in highly shade-tolerant species than in moderately shade-tolerant species. Seedlings of two evergreen conifers, shade-tolerant Abies alba Mill. and moderately shade-tolerant Picea abies Karst., and two deciduous angiosperm species, highly shade-tolerant Fagus sylvatica L. and moderately shade-tolerant Acer pseudoplatanus L., were grown in deep shade (LL, 5% of full irradiance) or in full solar irradiance (HL) during 2003 and 2004. Steady state responses of quantum yield of PSII (Phi(PSII)), apparent electron transport rate (ETR), nonphotochemical quenching (NPQ) and photochemical quenching (qP) were generally modified by the light environment, with slower declines in Phi(PSII) and qP and greater maximal ETR and NPQ values in HL plants in at least one season; however, no link between quantitative measures of plasticity of these traits and shade tolerance was found. Plasticity of nine anatomical traits (including palisade cell length, which was reduced in LL) showed no relationship with shade tolerance, but was less in conifers than in deciduous trees, suggesting that leaf life span may be a significant correlate of plasticity. When LL-acclimated plants were exposed to HL conditions, the degree and duration of photoinhibition (measured as a decline in maximum quantum yield) was greatest in F. sylvatica, much lower in P. abies and A. alba, and lowest in A. pseudoplatanus. Thus, as with the other traits studied, vulnerability to photoinhibition showed no relationship with shade tolerance.

Morphological and physiological adjustments of Brazilwood (Caesalpinia echinata Lam.) to direct solar radiation

“…On the other hand, the P.I. of morphological (SLA, anatomical components and water content) and biochemical (photosynthetic pigments) components were higher in new leaves, confirming earlier reports according to which the highest adaptations occur in the leaves in full sun (Kursar and Coley, 1999;Wyka et al, 2007).…”

“…From each plant, four leaf discs with diameter of 4.5 mm were homogenized in 5 mL of dimethyl-sulfonamide saturated with CaCO 3 in test tubes spin-coated with aluminum foil and incubated at 60 o C for 5 h (Wyka et al, 2007). Optical density readings were performed using a spectrophotometer (FEMTO, 700 Plus, SP) at 470, 663 and 645 nm and the concentrations of pigments determined by the equations of Lichtenthaler (1987).…”

“…The physiological adjustments of shade plants when exposed to high radiation also involve the decreased concentration of total chlorophyll (Chl total ) or an increase in the ratio of xanthophylls and violaxanthin cycle in relation to Chl total (Wyka et al, 2007;Melgar et al, 2009). Under intense irradiance, some trees present inhibition of photosystem II (PSII) electron transport associated with the higher concentration of carbohydrates (Valladares et al, 2005;Melgar et al, 2009) and increased levels of flavonoids (Tattini et al, 2006).…”

“…Morphological and physiological changes in response to variations in irradiance intensity are well documented for leaves of trees in temperate zones (Matsuki et al, 2003;Valladares et al, 2005;Urban et al, 2007;Wyka et al, 2007). For the tropical trees, especially those native to Brazilian forests, there are increasing ongoing investigations which will bring answers in the medium term (Souza and Válio, 2003;Mengarda et al, 2009).…”

Relações do N, P e K com a fluorescência da clorofila, teores de nutrientes foliares e carboidratos solúveis do caule de Caesalpinia echinata Lam.

“…Para isso retiraram-se quatro discos foliares de 0,45 cm de diâmetro com o auxílio de um perfurador de rolha e pesados para a obtenção da massa fresca. Os discos foram imediatamente colocados em tubos de ensaio contendo 5 mL de dimetil sulfóxido (DMSO) saturado com CaCO 3 e incubados no escuro a 60 °C por 5 horas (Wyka et al 2007). As leituras das absorbâncias foram realizadas nos comprimentos de onda de 470, 645, 663 nm e calculadas as concentrações dos pigmentos de acordo com as fórmulas de Lichtenthaler & Welbum (1983): Fluorescência da clorofila a -Para a avaliação da fluorescência da Clor a foram utilizados foliólulos da região mediana da primeira folha madura e completamente expandida das plantas 450 dias.…”