Energetic flux and performance index in copaiba (Copaifera multijuga Hayne) and mahogany (Swietenia macrophylla King) seedlings grown under two irradiance environments

Abstract

Plant adaptation under conditions of limited irradiance can be investigated by their efficiency while using the available energy with a minimal thermodynamic energy loss. For this reason, we compared the energetic fluxes and the performance index (PI ABS) in copaiba (Copaifera multijuga) and mahogany (Swietenia macrophyla) seedlings under both sunlight and shade. The experiment was carried out in Manaus (3º8'S, 59º52'W), Amazonas State, Brazil. The fluorescence transients were obtained in intact and healthy leaves using a Plant Efficiency Analyser (PEA) between 1200 h and 1300 h. Using the O-J-I-P test, the following parameters were calculated: 1) density of reaction centers per cross section (RC/CS), 2) maximum quantum yield for primary photochemistry of photosystem II (sigmaPo), and 3) probability of energy excitation (psio) or that of an absorbed photon (sigmaEo) to move an electron further than quinone A, and 4) the performance index (PI ABS). The highest PI ABS was found in seedlings under shade for both species. Mahogany seedlings exhibited values of PI ABS about three-fold and 14-fold higher than copaiba seedlings under shade and sunlight, respectively. For RC/CS, reaction centers were inactive under sunlight, 58% for mahogany and 78% for copaiba. The high irradiance induced a decrease of sigmaPo in mahogany (36%) and in copaiba (69%) when compared to shaded seedlings. This likely was a result of need for excess energy dissipation under sunlight. In addition, it was verified that seedlings under sunlight presented a severe decrease in sigmaEo, particularly in copaiba (23-fold), when compared to mahogany (9fold). Therefore, mahogany seedlings showed the highest performance in energy use under low and high irradiance, thus it may be proposed that mahogany presented lower entropy than copaiba seedlings, as demonstrated by the higher plasticity in the use of energy.

How does Cariniana estrellensis respond to different irradiance levels?

“…The majority of the Chl a fluorescence parameters in C. estrellensis showed better photochemical reactions of plants in partial shade by presenting low energy dissipation per active reaction centre (DI 0 /RC), low density of the reaction centre (RC/ABS), and higher performance indices (PI ABS and PI TOTAL ) under 1400 lmol m -2 s -1 PAR. This information may be confirmed by analysing the higher quantum yield of electron transport from Q A to FSI (RE 0 /ABS), and PI TOTAL in 1400 lmol m -2 s -1 PAR difference of two climax species from the Amazon that showed higher performance indices in deep shade at 100 lmol m -2 s -1 PAR when compared to full sunlight (Gonçalves et al 2007). …”

Análise dos transientes da fluorescência da clorofila a de plantas jovens de Carapa guianensis e de Dipteryx odorata submetidas a dois ambientes de luz

“…A elevada irradiância provocou, nas plantas exposta ao sol, modificação no transiente OJIP com conseqüente diminuição dos valores de F m , conforme observado em plantas de copaiba (Copaifera multijuga Hayne) e de mogno (Swietenia macrophylla King) crescendo sob dois ambientes de irradiância (Gonçalves et al, 2007). Normalmente, quando as plantas estão sob ambientes estressantes, o tipo de estresse não é claramente identificado pelo transiente da fluorescência da clorofila a quando os dados são apresentados na forma linear, contudo, quando os valores do transiente OJIP são apresentados na forma variável relativa verifica-se, (Lichtenthaler et al, 1998).…”

“…Quando as plantas não estão sob efeito de determinado estresse não se verifica desvio positivo quando os dados são normalizados e exibidos na banda-K (Tomek et al, 2001;Oukarroum et al, 2007). A banda-K, normalmente é observada em plantas submetidas a estresse por elevação da temperatura (Guissé et al, 1995), contudo, sob aumento da incidência de irradiância também se verificou tal comportamento, como observado em experimento realizado por Gonçalves et al (2007) e também verificado neste experimento (Figura 2). A presença da banda-K reflete uma inibição do complexo de evolução do oxigênio (OEC) e coincide com a limitação do lado doador do fotossistema II (Srivastava et al, 1997;Pospíšil & Dau, 2000;Tomek et al, 2001).…”

“…Estudos sobre exposição ao excesso de irradiância indicam que as plantas experimentam diminuição na eficiência do fotossistema II, com conseqüente mudança no direcionamento da energia fotoquímica por meio da dissipação (Castro et al, 1995;Demmig-Adams et al, 1996;Santos Jr. et al, 2006;Gonçalves et al, 2007). Recentemente, tais investigações têm sido realizadas com o uso de novas ferramentas que ajudam a elucidar o comportamento de plantas quando submetidas a situações de estresse.…”

Photosynthetic analyses of two native Atlantic Forest species in regenerative understory of eucalyptus plantation

“…Plants exposed to high levels of irradiance experience a reduction in the quantum efficiency of PSII and consequent changes in the directing of photochemical energy by means of NPQ (Castro et al, 1995;DemmigAdams et al, 1996;Santos Jr. et al, 2006;Gonçalves et al, 2007). Some species under this condition may present increased photosynthetic assimilation (Lichtenthaler and Burkart, 1999) and higher levels of carotenoids, which aid in the protection against photoinhibition (Demmig- Adams et al, 1989).…”