Photosynthetic acclimation to high light conditions in mature leaves of Coffea arabica L.: role of xanthophylls, quenching mechanisms and nitrogen nutrition

Young coffee plants (Coffea arabica L. cv. Catuai), originally from a shade d habitat, were separated in three groups to be grown under different level s of N fertilization: 0.3 mmol N supplements were given to the soil every 7 days (high N treatment, 2N), every 15 days (medium N treatment, 1N) and ev ery 45 days (low N treatment, 0N). These plants were later exposed to a hig h sunlight irradiance (noon PPFD up to 1500 mu mol m(-2) s(-1)) for a perio d of 12 or 15 days. Among others, the values of electron transport capacity , maximum carboxylation activity, photosynthetic capacity (A(max)) and seve ral fluorescence parameters (F-v/F-m, F-v'/F-m', q(P), phi(e)) first showed a reduction (until the 4th-7th day) in all N treatments, followed by an N- dependent recovery. The 2N plants were less affected in the first few days and, at the end of the stress period, showed a better recovery for most of the studied parameters and the highest increase in the saturating PPFD for net photosynthesis and Amax. The present work shows that the ability to acc limate displayed by the mature leaves of 2N plants was accompanied by an in crease in energy dissipation mechanisms. These include an increase in the ' high energy' quenching and, mostly, the presence of higher contents of some xanthophylls (zeaxanthin and lutein) and carotenes, which helped to decrea se the energetic overcharge in the photosystems. Pigment changes in mature leaves suggest that N can promote specific mechanisms of acclimation others than those that might be expected from a preferential partition of the ele ment N into photosynthetic components.