Abstract

A Chilean guava ecotype (Ugni molinae Turcz.) was cultivated in Santiago during the summer of 1999/2000 in order to assess the effect of shading on photosynthesis. Plants were grown under either 50% shading or full sunlight and chlorophyll fluorescence, net assimilation rates of CO2, photosynthetic pigment contents, were measured 2 months after planting, in each light regime, during the day. The capacity to recover the photochemical efficiency of photosystem II in light grown plants, measured as Fv/Fm after 30 min dark adaptation was markedly reduced, reaching values lower than 0.5 at midday, with a sunlight PPFD of 1600 ?mol m-2 s-1. On the other hand, the shaded plants showed a nearly complete recovery of the parameter. The photochemical quenching of chlorophyll fluorescence, reached a value of 0.47, also at midday, in full light grown plants, nearly half that observed in the shade, indicating a high PSII excitation pressure in the former. The light saturated net CO2 assimilation rates, measured in controlled conditions of temperature, were markedly lower in the full light plants compared to the shade ones. It is concluded that the Chilean guava is not able to cope with the light intensities characteristic of many Mediterranean climates, resulting in chronic photoinhibition. © 2003 Elsevier Science B.V. All rights reserved.