Crescimento, fotossíntese e mecanismos de fotoproteção em mudas de café (Coffea arabica L.) formadas a pleno sol e à sombra / Growth, photosynthesis and mechanisms of photoprotection in coffee (Coffea arabica L.) seedlings grown under full sunlight and shade

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Coffee seedlings have been traditionally grown in shaded nurseries. However, some coffee growers, with the aim of improving acclimation after moving the seedlings from the nursery to the field, are growing the seedlings under full sun. Nonetheless, most information associated with cultivation of coffee seedlings under varying light is restricted to simple morphological evaluations, with no emphasis on physiological traits linked to the mechanisms of acclimation of coffee seedlings to light availability. In this study morphological, physiological and biochemical traits were examined in leaves from coffee seedlings grown in the open and under shade. Dry biomass accumulation and relative growth rate (RGR) were unresponsive to growth conditions. Shoot biomass allocation and leaf mass ratio were smaller in full sun-grown seedlings (T1) than in their shade-grown counterparts (T2). As a whole, this behavior should be associated with the larger net assimilation rate (NAR) of T1 seedlings. The maximum net CO2 assimilation rate (A) was larger in T1 plants, although the diurnal time-course of leaf gas exchanges was similar when comparing T1 andT2 seedlings. Changes in day closely accompanied those of stomatal conductance (gs). Light-induced alterations in total chlorophyll (Cl(a+b)) concentration as well as in Cl a/b ratio were not found Similarly, no sign of of chronic photoinhibition of photosynthesis or oxidative damages were found in T1 and T2 seedlings; as a result, malondialdehyde concentration was similar in these kinds of seedlings. The larger excitation pressure imposed to T1 seedlings was properly dissipated, a fact likely associated with the greater non- photochemical quenching coefficient [that in turn was linked to a larger deepoxidation state of the xanthophyll pools (DEPS), higher amounts of zeaxanthin, and higher ratio of zeaxanthin + violaxanthin + antheraxanthin + zeaxanthin to total carotenoid as well as with the larger enzyme activities of the antioxidant system, particularly the ascorbate peroxidase glutathione reductase and catalase. Decreases in A, observed after moving the seedlings from the shade to the open (T3) were likely to have been associated with reductions in gs as well as with chronic photoinhibition. Decreases in Cl (a+b) and smaller activities of antioxidant enzymes, associated with an accumulation of MDA, were observed in T3 seedlings. These seedlings exhibited, even before dawn, pronounced nocturnal retention of zeaxanthin and remarkable increases in DEPS; however T3 seedlings showed an insufficient ability to be protected against the the high irradiance. It is demonstrated here that formation of coffee seedlings under full sun is a good option that should be considered by the coffee growers due mainly to the superior performance of sun-grown seedlings over that of shade- grown counterparts.

ASSUNTO(S)

produção de mudas seedling production photosynthesis fisiologia vegetal coffea arabica coffea arabica fotossíntese

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