Nutrient cycling in bromeliad phyllosphere

Background/Question/Methods

Plant phyllosphere is inhabited by an incalculable diversity of microorganisms that may play numerous ecosystem functions. For example, bacteria from the phyllosphere may mineralize complex organic compounds and provide nutrients to plants through their thin cuticle and stomata. However, the plant ability to absorb water and solutes of low molecular weight through leaves is specially exploited in agronomic practices. In this study we predict that microorganisms that live on plant phyllosphere may mineralize complex organic nitrogen compounds (leaves, animal carcasses) into simple compounds that may be absorbed by leaves. Thus, we expect that plants with complete bacterial assemblages can improve plant nutrition and development. This prediction was tested using the terrestrial bromeliad Bromelia balansae, associated mutualistic spiders (Psecas chapoda), and bacteria on its phyllosphere. In greenhouse experiments, we handled bacterial abundance with antibiotics and use ¹⁵N labeled debris from bromeliad-living animals and physiological methods to test bromeliad nutrition and growth.

Results/Conclusions

Debris from bromeliad-living animals contributed 10.7 ± 1.9% (mean ± standard error) of nitrogen in bromeliads that had their bacteria density reduced; in contrast, in the presence of the whole bacterial assemblage bromeliad-living animals contributed 27.1 ± 4.4% of bromeliad nitrogen. Additionally, bromeliads with the whole bacterial assemblage accumulated 57% more soluble protein and grew 13% more than bromeliads that had bacteria reduced with antibiotics. These results indicate that bacteria can accelerate nutrient cycling in the phyllosphere of bromeliads and improve plant nutrition and development. In certain biomes, as the Atlantic Forest, up to 13 million of bacterial species may live on the phyllosphere. These microorganisms may perform many unknown ecological functions, as the nutrient cycling in the phyllosphere of plants. It is known that the acquisition of nitrogen through plant phyllosphere is the main mechanism for nitrogen uptake in nutrient-poor, humid tropical soils. Bacteria from the phyllosphere that mineralize organic compounds may play an important role in nutrient dynamics in tropical forest canopy.

Financial Support: FAPESP