The role of multiple partners in the digestive mutualism with a protocarnivorous plant

Background/Question/Methods

The protocarnivorous plant Paepalanthus bromelioides (Eriocaulaceae) is similar to bromeliads in that this plant has a rosette-like structure that allows rainwater to accumulate in leaf axils (i.e., phytotelmata). Although the rosettes of P. bromelioides are commonly inhabited by predators (e.g., spiders), their roots are wrapped by a cylindrical termite mound that grows beneath the rosette. We predict that these plants can derive nutrients from recycling processes carried out by termites and from predation events that take place inside the rosette. We also predict that bacteria living in phytotelmata can accelerate nutrient cycling derived from predators. We tested our predictions by performing field experiments (rocky fields from Serra do Cipó, Brazil) with isotopic methods of ¹⁵N.

Results/Conclusions

Analyses of ¹⁵N in natural abundances showed that the isotopic signature of P. bromelioides is similar to that of carnivorous plants and higher than that of non-carnivorous plants in the study area. Linear mixing models showed that the addition of labelled insects and spider faeces resulted in nitrogen contributions of 8.6 ± 1.1% (SE) and 19 ± 3.1% to the total nitrogen of P. bromelioides, respectively. Although the plants of P. bromelioides associated with termites were enriched with more ¹⁵N compared to those not associated with termites, we did not detect nitrogen flux from termites to plants via decomposition of labelled cardboard. Bacteria did not affect nutrient cycling or nitrogen uptake from prey carcasses and spider faeces. Our results suggest that P. bromelioides derive nitrogen from associated predators and termites, despite differences in nitrogen cycling velocities, which were higher in nitrogen derived from predators (leaves) than from termites (roots). This is the first study that demonstrates partitioning effects from multiple partners in a digestion-based mutualism. Paepalanthus bromelioides bears all the attributes necessary to be considered as a carnivorous plant in the context of digestive mutualism.

Finnancial Support: FAPESP