Photosynthesis and photoinhibition in mahogany and acariquara as a function of irradiance and leaf temperature

Abstract

Photoinhibition may be exacerbated by stress factors such as high temperature. The aim of the work was to determine the effects of temperature and irradiance on photosynthesis and photoinhibition in mahogany (Swietenia macrophylla King) and acariquara (Minquartia guianensis Aubl.). Also to assess the effect of irradiance and temperature on the recovery from photoinhibition at low irradiance. Sapling were grown at low irradiance: 0.20 mol m-2 day-1 (mahogany) and 1.43 mol m-2 day-1 (acariquara). Photosynthesis and fluorescence characteristics were assessed in plants subjected to two irradiances 1,000 and 1,700 μmol m-2 s-1, and two temperatures, 32 e 38°C. At 32°C, light saturated photosynthesis (Amax) was greater in mahogany than in acariquara. Mahogany plants exposed to 38°C showed a consistent decline in carbon uptake, and after 50 min both species showed the same photosynthetic rates. In saplings exposed to 32°C, increase in irradiance, from 1,000 to 1,700 μmol m-2 s-1, exacerbated photoinhibition, but without reducing Amax values. At 1,700 μmol m-2 s -1, the rise in temperature, from 32 to 38°C, did not increase photoinhibition. After 72 hours at low irradiance, recovery from photoinhibition was 80% in acariquara and 89% in mahogany. There was no effect of leaf temperature on photoinhibition.