Functional traits associated to photosynthetic plasticity of young Brazil nut (Bertholletia excelsa) plants

Abstract

The Brazil nut shows the ability to establish itself in contrasting irradiance conditions. However, physiological strategies with respect to acclimatization to different irradiance still remain unknown. Here we investigated the leaf traits variations related to photosynthetic plasticity of Bertholletia excelsa. In this study, B. excelsa saplings were acclimated during 90 days (PPFD = 30 μmol m−2 s−1) and after the acclimatization, the saplings were subjected to two irradiance conditions: planting in full sun (100% PPFD) and planting in forests (1.5% PPFD). Following this, the specific leaf mass (SLM), gas exchange, maximum yield of photochemistry (FV/FM), chlorophyll and carbohydrate contents were evaluated. Net photosynthesis per unit area (Pn) of saplings in full sun was 2 times greater than in shade and photosynthesis in full sun was positively related to stomatal condutance (gs), dark respiration (Rd), carbohydrates and SLM. On the other hand, in shade, we observed an increase in the apparent quantum yield (α) and a reduction of SLM. Although B. excelsa reduced FV/FM by 30% in full sun, after 7 days it was able to recover from stress by the increase in irradiance. The traits that most contributed to explaining the photosynthetic plasticity were SLM (8.7%), FV/FM (7.7%), Rd (5.9%), gs (5.3%) and sugar (5.2%). Therefore, the fast recovery of photosynthesis during light stress and adjustments of morpho-functional traits in leaves to irradiance in B. excelsa are strong candidates to explain why this species establishes both in environments with low and high light availability.