Initial development of carapa guianensis aubl. plants under different shading levels: a two-year study on growth and physiological variables

Resumen

Carapa guianensis Aubl. (andiroba in Brazil) is an Amazonian multi-use tree. Due to an increased early growth (caused by large seeds reserves), no conclusive data on light preferences during initial development are available. This two-year greenhouse experiment aimed to evaluate growth and physiological variables under four levels of shading (0%, 30%, 50% and 70%). In the very-early stage of Carapa guianensis development (≤ 15 months), the growth in height, leaf number did not give conclusive results. Nevertheless, the shoot diameter and the relative chlorophyll content (SPAD) significantly indicated more efficient carbon gain by photosynthesis in high shade conditions (70%). After 15 months, significant changes suggested photoinhibition and high plasticity: i) gas exchange measurements (photosynthetic activity, stomatal conductance and transpiration) showed lower values under sun conditions, ii) the 50%-shade resulted in the highest dry matter increase (regarding leaves, stem and roots), iii) the Shoot-Root Ratio varied from 1.88 under sun exposure up to 4.73 under shade conditions. Although plantations of Carapa guianensis are often performed under open conditions, this study indicates that this species can give a higher return regarding biomass under shaded conditions, at least during the initial phase of establishment.