Federal and state agencies have begun using residual genetic information taken from the environment—environmental DNA or eDNA—to help make management and regulatory decisions. Environmental DNA can provide information from water, soil, or air samples about the living parts of ecosystems with unprecedented scope, in some cases providing broad surveys of the species present and in others pinpointing hard-to-find species. However, standards for analysis and interpretation have only recently begun to arise in the nascent field of eDNA analysis. As this new and valuable source of information begins to influence the implementation of environmental laws, we survey existing federal uses of eDNA and review federal information requirements relevant to natural resource management—in particular, under the data-hungry Endangered Species Act and National Environmental Policy Act. We find that some agencies are already using eDNA data, and, for the most part, these uses are likely to meet the legal requirements of the controlling statutes and regulations. Though legally acceptable, social factors influence the degree to which a technology becomes widespread in agency practice. We survey likely future scenarios for eDNA uptake and offer recommendations for driving broader adoption of this useful technology and enabling management and regulatory decisions grounded in eDNA as a data source.

Legume crops establish beneficial associations with rhizobial bacteria that perform biological nitrogen fixation, providing nitrogen to plants without the economic and greenhouse gas emission costs of chemical nitrogen inputs. Here, we examine the influence of three environmental factors that vary in agricultural fields on strain relative fitness in nodules.

Spatial and temporal variation in resource availability, population density, and composition likely affect the ecology and evolution of symbiotic interactions. We examined how host genotype, Nitrogen addition, rhizobial density, and community complexity affected a legume-rhizobia (Medicago truncatula - Ensifer meliloti) mutualism. Host genotype had the strongest effect on the size, number, and rhizobial composition of root nodules (the symbiotic organ). By contrast, the effect of small changes in N-availability and the complexity of the inoculum community (2, 3, 8, or 68 strains) were minor. Higher inoculum density resulted in a nodule community that was less diverse and more beneficial but only in the more selective host. With the less selective host, higher density resulted in more diverse and less beneficial nodule communities. Density effects on strain composition deserve additional scrutiny as they can create eco-evolutionary feedback and have translational relevance for overcoming establishment barriers in bio-inoculants.Short AbstractThe environmental context of the nitrogen-fixing mutualism between leguminous plants and rhizobial bacteria varies over space and time. The understudied environmental variable of rhizobial density had a larger effect on the relative fitness of 68 rhizobia (Ensifer meliloti) strains in nodules than the addition of low-levels of nitrogen or community complexity.