Comparative leaf ecophysiology and anatomy of seedlings, young and adult individuals of the epiphytic aroid Anthurium scandens (Aubl.) Engl.

Usually dry and oligotrophic, canopies can impose stressful conditions on plant survival. Adaptations to life in the canopy have been examined extensively for Bromeliaceae, Orchidaceae and Polypodiaceae, but not for Araceae. These four families comprise nearly 80% of all vascular epiphytic species. Recent data indicate that ontogenetic and size-related changes in anatomy and ecophysiology affect the performance and survival of epiphytes in the field. Therefore, to better understand how Araceae species have successfully adapted to the epiphytic habitat, we studied the holoepiphyte Anthurium scandens in relation to stomatal and epidermal conductance, leaf succulence, sclerophylly, leaf nitrogen content and retranslocation, and quantitative anatomy. Analyses were performed for leaves of seedlings, young and adult individuals. First, results showed that the stomatal conductance of young and adult individuals was similar, with maximal daily conductance varying from 20 mmol m−2 s−1 in the dry period to 100 mmol m−2 s−1 after four continuous rainy days. We concluded that stomatal conductance is highly dependent on water availability at the root level for both ontogenetic phases. Second, in comparison to young and adult individuals, seedlings had higher epidermal conductance to water loss as well as lower values of leaf succulence and sclerophylly. Third, although both young and adult individuals had similar leaf nitrogen content in green mature leaves, higher retranslocation rates of leaf nitrogen during senescence were found in adult individuals. Fourth, young and adult individuals presented leaves with similar quantitative anatomy, but with higher values in comparison to seedling leaves, with the exception of the higher adaxial and abaxial thickness of epidermal cells. Finally, in addition to mesophytic anatomical characters, results showed that leaves of A. scandens seedlings had lower succulence, sclerophylly and resistance to water loss, indicating a higher potential susceptibility to stressful abiotic conditions in comparison to young and adult individuals. Based on these findings, we suggest that this higher susceptibility of seedlings to abiotic stress helps explain the establishment and distribution of A. scandens in the more mesic micro-sites of the canopies.