Direct nitrogen intake by petals

Flowers are more than objects that awaken passions: they were key evolutionary innovations leading to rapid diversification and the current dominance of flowering plants in terrestrial ecosystems. However, the major biological function that has been ascribed to petals is the mediation of interactions with pollinators. Here we show that petal surfaces can effectively capture and quickly allocate nitrogen ions available in wet atmospheric deposition into ovaries and developing seeds. In laboratory and field experiments we used ¹⁵N stable isotope at trace concentrations and measured petal intake in five species from five different families. We observed significant ¹⁵N increases in fully developed seeds when petals were exposed to ¹⁵N, contrasting with the lack of seed enrichment when ¹⁵N was applied just to soil or foliage. Translocation of ¹⁵N through petals occurred in a matter of hours, and mass recovery rates of isotope tracers in seeds were much higher through petals (44.6%) than soil (7.4%) or leaves (0%). Our experiments suggest that when reactive N is available from atmospheric sources, flower petals could act as permeable surfaces that can help reproductive structures meet demands of limiting nutrients.