Plants form alliances with microbes in the soil in which they grow. Legumes, for example, benefit from a symbiotic relationship with microbes that inhabit nodules in their roots and “fix” nitrogen in the atmosphere to make it available to promote the legumes’ growth. But are microbes always beneficial to plants? Or does competition between strains for plant access degrade the service the bacteria ultimately provide? A team led by scientists at the University of California, Riverside, set up experiments to answer these questions and better understand the competition process. The researchers used a native California plant with nodules, Acmispon strigosus, and a set of eight compatible nitrogen-fixing bacterial strains. They infected some plants with each of the eight strains to directly measure their ability to infect the plants and provide benefits. They then infected other plants with pairs of bacterial strains to assess the competitive ability of each strain and the effect on plant performance. The researchers found that competition between strains of beneficial bacteria in the soil degrades the service that the bacteria provide to their hosts.