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

Abstract

This study aimed to characterize the alarm and resistance phases of stress of Caesalpinia echinata under intense irradiance in order to better define its position on forest succession. The alarm phase was identified by rapid reduction in the maximum quantum yield of PSII primary photochemical reactions (φP0 = F V /F M ) and Performance Index (PI ABS ) followed by total leaf abscission in the first week of exposure to direct sunlight. The new leaves grown showed recovery of chlorophyll a parameters, increase in blade thickness, elongation of the palisade and spongy parenchymas, higher water content, and reduction of specific leaf area. These changes were associated with the osmoprotector of sucrose and antioxidative of raffinose effects, which indicate an efficient adjustment system to intense irradiance in the resistance phase of stress. However, the continuous decrease in photosynthetic pigments in the resistance phase combined with the photodamage in the fluorescence of Chl a and total abscission of leaves in the alarm phase are strong indications that C. echinata is a shade and late or climax species in forest succession.

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.…”

“…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. The highest chlorophyll content and lower Chl a:b ratio under shading compared to full sun indicates a higher proportion of complex light energy collectors in an effort to optimize photochemical efficiencies found in Amazon rainforest species .…”

“…Although high irradiance increased DI 0 /RC, decreased TR 0 /ABS and ET 0 /ABS, and inhibited PSII (Xiang et al 2013), consequent to the oxidative effect of reactive oxygen species (Sielewiesiuk 2002), photodamage in C. estrellensis was avoided in higher irradiances due to the antioxidant action of fructose and sucrose (Mengarda et al 2012). Soluble carbohydrates of low molecular weight act not only as osmoprotectants and stabilizers of cellular membranes but also as scavengers of ROS, and they play a novel role in the protection of photosynthesis from oxidative damage caused by environmental stress (Nishizawa et al 2008).…”

“…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).…”

“…Under full sunlight, Mengarda et al (2009) observed that C. echinata plants tolerated high irradiance, although they had decreased photosynthetic rates (A) and photosystem II photochemical efficiency (F V /F M ). The capacity of C. echinata to tolerate high irradiance was associated with increased soluble carbohydrate concentrations, increased length of mesophyll cells, higher water contents, and improved recovery of the photochemical capacity of plants transferred to full sunlight (Mengarda et al 2012).…”