Ants are less attracted to the extrafloral nectar of plants with symbiotic, nitrogen-fixing rhizobia

作者：Godschalx Adrienne L^*; Schaedler Martin; Trisel Julie A; Balkan Mehmet A; Ballhorn Daniel J

来源：Ecology, 2015, 96(2): 348-354.

DOI：10.1890/14-1178.1

• ant plant
• cyanogenesis
• direct defense
• extrafloral nectar
• indirect defense
• lima bean
• multitrophic interactions
• mutualism
• nitrogen fixation
• plant defense
• plant resource allocation
• rhizobia

Plants simultaneously maintain mutualistic relationships with different partners that are connected through the same host, but do not interact directly. One or more participating mutualists may alter their host's phenotype, resulting in a shift in the host's ecological interactions with all other mutualists involved. Understanding the functional interplay of mutualists associated with the same host remains an important challenge in biology. Here, we show belowground nitrogen-fixing rhizobia on lima bean (Phaseolus lunatus) alter their host plant's defensive mutualism with aboveground ants. We induced extrafloral nectar (EFN), an indirect defense acting through ant attraction. We also measured various nutritive and defensive plant traits, biomass, and counted ants on rhizobial and rhizobia-free plants. Rhizobia increased plant protein as well as cyanogenesis, a direct chemical defense against herbivores, but decreased EFN. Ants were significantly more attracted to rhizobia-free plants, and our structural equation model shows a strong link between rhizobia and reduced EFN as well as between EFN and ants: the sole path to ant recruitment. The rhizobia-mediated effects on simultaneously expressed defensive plant traits indicate rhizobia can have significant bottom-up effects on higher trophic levels. Our results show belowground symbionts play a critical and underestimated role in determining aboveground mutualistic interactions.

• 出版日期2015-2