Optimisation of spatial allocation patterns in lianas compared to trees used for support

摘要

There are only limited possibilities to study the competition between trees and lianas in the top canopy of tropical rain forests. Furthermore, the important question how the leaf traits are related to twig support is rarely studied, especially regarding growing space partitioning between the self-supporting and the climbing growth form. Our study used the hot-air balloon within the "Operation Canopee" in the Masoala National Park, Madagascar, to test the differences in spatial allocation patterns of leaves and twigs in lianas and tree parts used for support. The sampling design emphasised to obtain a common assembly of twigs and leaves from both, trees and lianas. The results from the top canopy were compared to the data from the understorey regarding biomass and nutrients in leaves and distal twigs. In the understorey the reduction in structural investment was much stronger in lianas than in trees. The results showed that lianas reduced carbon investment per volume, but increased leaf nitrogen concentration and leaf area ratio (LAR), the latter driven by a reduction in leaf mass per area (LMA). In the top canopy, lianas contributed about one third of the leaf area density of 3 m(2) m(-3). For distal twigs, no relationship was found between twig biomass per volume and leaf area density for trees, but lianas balanced both structural parameters closely. The climbers benefit from the external support provided by the trees and optimise the area of assimilation tissue at low per volume investment for mechanical stability. Several traits such as low LMA and high leaf nitrogen concentrations together with higher LAR and optimised spatial investment advantage the climbing growth form and enable a fast acquisition of growing space. The results emphasize the necessity to consider spatial and structural features of growing space acquisition when dealing with plant competition.