Seasonal changes in photoprotective mechanisms of leaves from shaded and unshaded field-grown coffee (Coffea arabica L.) trees

Abstract

Coffee is native to shady environments, but often grows and yields better without shade. Thus, it may be reasoned that coffee leaves should display enough plasticity to acclimate themselves to contrasting light environments. However, little is known about mechanisms associated with such plasticity in coffee. This work aimed, therefore, to explore differences in leaf photoprotective mechanisms. Plants were grown in the field and received either 48 or 100% natural light. Evaluations were made using outer leaves from the sun-facing sides of the coffee hedgerow in Viçosa (Brazil) in August and October, when growth and photosynthetic rates are expected to be minimal and maximal, respectively, and in December, when temporary depressions in those variables are common. Regardless of light treatments, coffee leaves showed: (1) very low photosynthetic rates (generally below 2.5 lmol m -2 s -1 ), (2) chronic photoinhibition in August (dry, cool season) that was accompanied by strong loss of pigment concentration, and (3) discrete, dynamic photoinhibition in October and December (rainy, warm season). Compared with shaded leaves, sunlit leaves generally exhibited lower pigment concentration, lower quantum yield of electron transport, steeper inclinations and similar electron transport rate. Total ascorbate pool tended to be larger in sunlit than in shaded leaves (but with similar redox state), whereas activities of key antioxidant enzymes, as well as malondialdehyde accumulation and electrolyte leakage, were similar between those leaf types. As a whole, the photosynthetic apparatus of the coffee tree showed a low phenotypic plasticity to varying irradiance.

Continuous planting under a high density enhances the competition for nutrients among young Cunninghamia lanceolata saplings

“…On the other hand, a high planting density may increase the intensity of the competition. In trees, the increase in the chlorophyll pigment and the decrease of the Chl a/Chl b ratio are characteristics of the shaded leaves (Sarijeva et al 2007;Chaves et al 2008;Lichtenthaler et al 2013). In this study, the high light compensation point and chlorophyll pigment content and a low Chl a/Chl b ratio clearly suggested that there were light limitations for plant growth under a high planting density.…”

Seasonal changes in the physiological activity of regeneration under a natural light gradient in a Pinus pinea regular stand

“…A decrease in Ψ has been related to a drop in the photochemical eff iciency of PSII (DemmigAdams et al, 1989;Epron et al, 1992). In addition, in the hottest days, one-year old seedlings showed the lowest Φ PSII values, related to the low Fv/Fm and as an indirect inference of its increased capacity to dissipate excess excitation energy (Chaves et al 2008); while the oldest seedlings (class 4) showed the highest Φ PSII values.…”

Características fisiológicas e desenvolvimento de cafeeiros sob diferentes níveis de sombreamento

“…Several authors (Friend, 1984;Fahl et al, 1994;Morais et al, 2003;Nascimento et al, 2006;Araújo et al, 2008;Gomes et al, 2008;Chaves et al, 2008) observed an increase in the photosynthetic rate of coffee plant leaves under high radiation when compared with exposed shaded leaves. However, other authors found that coffee plants under shading present higher CO 2 assimilation (Nutman, 1937;Kumar & Tieszen, 1980;Freitas et al, 2003).…”

“…An increase in the net assimilation of CO 2 was observed in coffee plant leaves under high radiation when compared with shaded leaves exposed to lower radiation (Friend, 1984;Fahl et al, 1994;Morais et al, 2003;Nascimento et al, 2006;Araújo et al, 2008;Gomes et al, 2008;Chaves et al, 2008). Nevertheless, other authors found that coffee plants under shading present higher photosynthetic rates (Nutman, 1937;Kumar & Tieszen, 1980;Freitas et al, 2003).…”

“…However, in many situations, the coffee plant grew and had better production without shading. As a result, shading was abandoned in regions (DaMatta et al, 2007;Chaves et al, 2008) at the same time in which cultivars were being genetically improved to present high production under full sun conditions (DaMatta, 2004;Kanten & Vaast, 2006;Gomes et al, 2008).…”