Impacts of nitrogen addition on switchgrass root-associated diazotrophic community structure and function

Area of Science:

• Agricultural Science
• Microbiology
• Environmental Science

Background:

• Cellulosic bioenergy crops like switchgrass offer climate mitigation potential on marginal lands.
• Low-input agriculture is key for sustainable bioenergy systems.
• Associative nitrogen fixation (ANF) is a potential nitrogen source for bioenergy crops, but its contribution is unclear, especially with nitrogen fertilization.

Purpose of the Study:

• To investigate the structure and function of switchgrass root-associated diazotrophic communities.
• To determine the impact of long-term and short-term nitrogen (N) additions on ANF and diazotrophic communities in marginal lands.

Main Methods:

• Assessed ANF rates and diazotrophic community structure (nifH gene) in switchgrass roots.
• Utilized soil from three distinct marginal land sites.
• Applied long-term and short-term nitrogen additions.

Main Results:

• ANF rates were highly variable, often exceeding previously reported levels, and showed no consistent response to nitrogen additions.
• Nitrogen additions had minimal impact on the structure and membership of root-associated diazotrophic communities.
• A consistent diazotrophic community was observed in switchgrass roots, regardless of the initial soil community composition.

Conclusions:

• Root-associated diazotrophic communities can significantly contribute to switchgrass nitrogen requirements, independent of nitrogen fertilization.
• Switchgrass roots appear to select for specific diazotrophic communities, influencing nitrogen acquisition.
• This suggests a promising avenue for low-input, sustainable bioenergy production.