Photosynthesis and carbon gain under contrasting light levels in seedlings of a pioneer and a climax tree from a Brazilian Semideciduous Tropical Forest

Abstract

-(Photosynthesis and carbon gain under contrasting light levels in seedlings of a pioneer and a climax tree from a Brazilian Semideciduous Tropical Forest). In this study we evaluated photosynthetic characteristics and patterns of biomass accumulation in seedlings of two tree species from a Semideciduous Tropical Forest of Brazil. Seedlings of Trema micrantha (L.) Blum. (pioneer) and Hymenaea courbaril (L.) var. stilbocarpa (Hayne) Lee & Langenh. (climax) were grown for 4 months under low light (LL) (5%-8% of sunlight) and high light (HL) (100% of sunlight). Under HL, T. micrantha showed higher CO 2 assimilation rates (A CO 2 ) and light saturation than H. courbaril. Under LL, A CO 2 were higher in H. courbaril. Under LL, total chlorophyll and carotenoid contents per unit leaf area were higher in H. courbaril. Chlorophyll a/b ratio was higher in T. micrantha under both light regimes. A CO 2 and F v /F m ratio at both pre-dawn and midday in H. coubaril were lower in HL indicating chronic photoinhibition. Thus, the climax species was more susceptible to photoinhibition than the pioneer. However, H. courbaril produced higher total biomass under both treatments showing high efficiency in the maintenance of a positive carbon balance. Thus, both species expressed characteristics that favor growth under conditions that resemble their natural microenvironments, but H. courbaril also grew under HL. The ecophysiological range of responses to contrasting light levels of this climax plant seems to be broader than generally observed for other rainforest climax species. We propose that this could be related to the particular spatio-temporal light regime of the semideciduous forests.Key words -CO 2 assimilation, growth response to light, Hymenaea courbaril, photoinhibition, Trema micrantha RESUMO -(Fotossíntese e acúmulo de biomassa sob condições contrastantes de intensidade luminosa em plântulas de uma espécie pioneira e outra climácica de uma floresta estacional semidecidual do Brasil). Neste trabalho foram avaliadas características fotossintéticas e padrões de acúmulo de biomassa de duas espécies arbóreas de uma floresta estacional semidecidual. Plântulas de Trema micrantha (L.) Blum. (pioneira) e Hymenaea courbaril (L.) var. stilbocarpa (Hayne) Lee & Langenh. (climácica) foram cultivadas por quatro meses sob baixa radiação (BR) (5%-8% da radiação solar incidente) e alta radiação (AR) (100% da radiação solar incidente). Sob AR, T. micrantha apresentou maiores taxas de assimilação de CO 2 (A CO 2 ) e ponto de saturação luminosa. Sob BR, A CO 2 foram maiores em H. courbaril. Sob BR, o conteúdo de clorofilas e carotenóides totais por unidade de área foliar foi maior em H. courbaril. A razão clorofila a/b foi maior em T. micrantha sob os dois tratamentos. A CO 2 e razão F v /F m antes do amanhecer e no horário de máxima intensidade luminosa em H. courbaril foram menores sob AR, indicando a ocorrência de fotoinibição crônica. Apesar da suscetibilidade à fotoinibição, H. courbaril teve maior produção de biomassa. Dest...

Photosynthetic performance and anatomical adaptations in Byrsonima sericea DC. under contrasting light conditions in a remnant of the Atlantic forest

“…The fact that sun plants, such as B. sericea DC., are more photosynthetically active corroborates observations by other authors, who have shown that pioneer species have higher photosynthetic rates, especially in sunny environments Silvestrini et al, 2007). Moreover, during the rainy season, water conditions favor photosynthetic performance .…”

“…A higher light intensity directly influences community architecture (Souza et al, 2009) and floristic composition (Murcia, 1995), influencing the establishment of pioneer species. These species generally have higher photosynthetic rates with large accumulation of biomass and low susceptibility to photoinhibition, in comparison to climax species (Silvestrini et al, 2007).…”

“…Usually in the dry season there is a reduction in photosynthetic assimilation and transpiration as a consequence of reduced stomatal conductance . Many ecophysiological studies involving sun and shade plants have reported comparisons between plants of different successional stages (Souza et al, 2005;Silvestrini et al, 2007;Portes et al, 2008) or of the same species (Nobel, 1976;Dias et al, 2007;Li et al, 2009;Dai et al, 2009). Although studies relating several successional stages are extremely important for understanding the function of the species that integrate an ecosystem, studies involving only one successional group in different environmental conditions, after human impacts, may help to understand the effect of forest fragmentation on the adaptive responses of these plants.…”

How does Cariniana estrellensis respond to different irradiance levels?

“…The lowest Chl a and Chl b concentrations in full sunlight are typical for a sun-acclimated condition observed in other non-pioneer tropical tree species (Gonçalves et al 2001(Gonçalves et al , 2005. The decrease in Chl a and Chl b and lowest of the total Chl Total : Carot observed in C. estrellensis in full sunlight has also been observed in other tropical species (Gonçalves et al 2005;Silvestrini et al 2007;Mengarda et al 2012), suggesting a decrease in energy assimilation of the antenna system (Laisk et al 2005) and protection of photosystems from photo-oxidative damage under high irradiance levels ). Photo-protection was less related to the Chl a:b ratio which can either increase (Kitajima and Hogan 2003), decrease (Mengarda et al 2012), or remain unchanged (Gonçalves et al 2005;Silvestrini et al 2007) in some tropical species under full sunlight.…”

“…This is reflected in an increased leaf area ratio (LAR) and specific leaf area (SLA), and a decreased blade thickness because of the reduced elongation of mesophyll cells (Lambers et al 2008). These adjustments improve the capture of low light in highly shaded environments, where certain tropical tree species tend to have lower relative growth rates (RGR) (Souza and Válio 2003), higher chlorophyll concentrations (Gonçalves et al 2005), higher photosynthetic activity (Silvestrini et al 2007), and lower concentrations of soluble carbohydrates Mengarda et al 2012).…”