Morphophysiological responses of tree species under shading levels in the field as a function of climatic seasonality.

Characteristics associated with seasonality in Southern Brazil impose numerous restrictions on the growth of native species, and therefore, morphophysiological adaptations are necessary for the maintenance of metabolism. Identifying these responses allows for a more accurate indication of the suitability of species for locations with extreme climatic and soil conditions. The objective of this study was to evaluate the influence of shading levels (SL) and climatic seasonality on the morphophysiology of young Myrcianthes pungens (O. Berg) D. Legrand and Cupania vernalis Cambess plants in a subtropical region. Species of significant importance for restoration were subjected to four levels of shading (SL0, SL18, SL50, and SL70) and evaluated during contrasting seasons of temperature and growth (winter and spring). In winter, both showed an increase in specific leaf area and variation in the amount of chlorophyll a and b, mainly under SL50 and SL70, which optimized photosynthesis under reduced light, sunlight hours and solar radiation. The increase in radiation and air temperature in spring denoted greater maximum assimilation of CO₂ in plants under SL18, SL50 and SL70, which from the analysis of principal components can be justified by the characteristics of the microclimate generated in these environments. Therefore, to optimize growth, M. pungens and C. vernalis must be planted under 50% shading because of morphophysiological adaptations in plants during seasons with subtropical climatic characteristics.