Carapa guianensis Aubl., known as andiroba, is a multipurpose tree from the Amazon. Planted under environmental conditions, there is still no conclusive data on the light preferences of this species. Thus, the aim of this study was to evaluate growth and physio- logical variables at four shading levels (0%, 30%, 50% and 70%). In the first observation period (≤ 15 months), the relative chlorophyll content (SPAD index) indicated more efficient carbon gain by photosynthesis under shade conditions. Gas exchange measurements (20 months) allowed to conclude that the conditions of exposure to the sun caused photoinhibition. Dry matter evaluation (24 months) confirmed: 50% shade resulted in the greatest increase in dry matter for all plant parts (leaves, stems and roots). This study indicates that this species can give a greater return in relation to biomass under shading conditions, such as in secondary forest enrichment or agroforestry systems, at least in the initial phase of establishment.

Models that predict the stomatal conductance process (gs) for a given set of environmental conditions are important, as this process is the main mechanism that controls the gas exchange of terrestrial plants absorbing atmospheric CO2. This work presents the results of a simulation to observe the gs process as a function of soil water availability (WAP) using an ecosystem demography model (ED2.2). The results showed that the model was able to reproduce the seasonality of the gas observed in the field. During periods when there was WAP, gs increased and the lower availability of water in the soil for the plant led to reduced photosynthesis due to stomata closure, decreasing stomatal conductance to reduce water loss. The model results for gross primary productivity (GPP) were also similar to those observed in the field, varying around ≈24 MgC.ha-1.yr-1 for the rainy season and ≈23 MgC.ha-1.yr- 1 for the dry season (average 2002 to 2010). The assimilation of CO2 via NPP and stomatal conductance had an R2 of 0.7 indicating that the assimilation of CO2 was high when there was greater stomatal conductance, favoring the increase in aboveground biomass in the model.