Estrutura e funcionamento de copas em espécies arbóreas de cerrado com distintas fenologias foliares

Abstract

The relationships among shoot inclination, light interception, photosynthetic capacity along shoot, biomass partitioning in leaves and shoots and the canopy structure were investigated in deciduous, semideciduous and evergreen tree species in Cerrado vegetation. The principal aim was to investigate the functioning and the structure of the canopies in cerrado tree species. The central hypotheses was that deciduousness is a trait strongly related to both canopy structure and functioning, and this relation could be revealed by morphological features of shoots, leaves, and by means of photosynthetic capacity along the shoot. Deciduous species produces only one cohort of leaf during the year at the end of the dry season. Slanting (plagiotropic) shoots in deciduous species could be one way to avoid the foliage self-shading since the bud unfold. One specific hypothesis was that deciduous species have plagiotropic shoots and the irradiance intensity and the photosynthetic capacity would be similar along shoot. The plagiotropic shoots in deciduous would allow high individual leaf area, high leaf area per shoot and one relationship between shoot-leaf in favor of leaves. On the other hand, the high leaf exposition to intense irradiance along shoot probably is one factor that imposes the shedding of the whole foliage at the dry season. Semideciduous and evergreen species produce leaves continuously during the year. The retention of the half of the foliage as in semideciduous even at the peak of dry season demands protection as the foliage self-shading along the shoot. Therefore, semideciduous and evergreen species have erect (orthotropic) shoots with evident foliage self-shading along the shoot. The light extinction along the orthotropic shoots could be one protection against excessive input of energy, especially in dry season. On the other hand, the dissimilar irradiance distribution along the shoot could result in significant difference about photosynthetic capacity between shaded basal and sunlit distal leaves on shoots. Semideciduous and evergreen species have higher number of canopy ramification than the deciduous species by reason of greater shoot emission at every season. This high canopy ramification in semideciduous and evergreen species could be revealed from one network representation with basic components as nodes and links. We supposed that links could be the shoots and nodes the nodal region where the shoots are emitted from the parental shoots. This representation could reveal structural differences in canopies of deciduous, semideciduous and evergreen species. These differences could be uncovered by the number of ramification and by the number of nodes in each leaf phenological group. Therefore, the link/node ratio and the frequency of shoots per node could reveal structural aspects significantly different across leaf phenological groups in 15 tree species studied here growing in a cerrado stricto sensu physiognomy.