Leaf allocation patterns and 13C and 15N natural abundances of tropical lianas (Passiflora sp.) as dependent on external climbing support

The transformation from self-supporting lianas to host-supported climbing lianas is related to re-allocation of biomass and nutrients among plant organs. Therefore, first, variations in leaf mass per area (LMA), leaf carbon and nitrogen allocation and ¹³C and ¹⁵N natural abundances were analysed among three tropical Passiflora species (P. edulis, P. ligularis, and P. tripartita) in a greenhouse study. Second, the influence of a climbing support was considered for each species and parameter. P. ligularis leaves were most enriched in ¹³C in both treatments when compared with the other two species. This enrichment was caused by a high LMA, which is related to a high internal resistance to CO₂ diffusion. For P. edulis and P. tripartita, δ¹³C was additionally increasing with nitrogen content per area. Generally, there were no differences when considering carbon and nitrogen allocation to leaves of host-supported and self-supporting lianas. The only hints towards increased investment into leaves after the transition from self-supporting to host-supported stages could be seen by a trend to increased leaf areas and masses. δ¹³C values of supported P. edulis or P. tripartita plants were significantly increasing faster than those of non-supported plants once the interactions of leaf mass or nitrogen content per area were accounted for. Hence, the offer of a climbing support had only a minor impact on δ¹³C or δ¹⁵N values in vitro, but this could be different with increasing age of lianas in vivo.