Long-term nitrogen fertilization induces legume-rhizobium mutualism meltdown.

After 33 years of nitrogen fertilization, legume–rhizobium symbioses show a mutualism meltdown marked by a beneficial symbiont declining in abundance and in host-beneficial allele proportion.

• Why it matters: Long-term nitrogen inputs can reshape soil microbial communities, but the evolutionary and ecological mechanisms behind breakdown of legume–rhizobium mutualism remain unclear.
• What they did: Bedwell et al. used long-read sequencing plus functional gene analysis to characterize nodulating and nonnodulating Rhizobiaceae and track changes in host-beneficial alleles.
• The result: The beneficial symbiont’s reduced abundance and lower proportion of host-beneficial alleles suggest evolutionary and ecological processes that destabilize mutualism under prolonged N fertilization.

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