Temporal dynamics of free-living nitrogen fixation in the switchgrass rhizosphere

• Main Authors: Evans, S.E (Author), Friesen, M.L (Author), Smercina, D.N (Author), Tiemann, L.K (Author)
• Format: Article
• Language: English
• Published: John Wiley and Sons Inc 2021
• Subjects: bacterium; bioenergy; Biofuels; Biological factors; Climate variables; community composition; Community composition; Cropping systems; Crops; diazotroph; energy crop; free-living nitrogen fixation; grass; High temporal resolution; marginal land; microbial community; nitrogen fixation; Nitrogen fixation; Panicum virgatum; plant nitrogen demands; Plants (botany); rhizosphere; Soil moisture; Soil moisture availability; sustainable bioenergy; switchgrass; Temporal dynamics; Temporal sampling; temporal variation
• Online Access: View Fulltext in Publisher

 Free-living nitrogen fixation (FLNF) represents an important terrestrial N source and is gaining interest for its potential to contribute plant available N to bioenergy cropping systems. Switchgrass, a cellulosic bioenergy crop, may be particularly reliant on FLNF when grown on low N systems, like marginal lands. However, the potential contributions of FLNF to switchgrass as well as the controls on this process are not well understood. In this study, we evaluated drivers of FLNF rates and N-fixing microbial (diazotrophic) community composition in field-grown switchgrass systems over two growing seasons with high temporal sampling. We found that climate variables are strong drivers of FLNF rates in switchgrass systems, compared to other environmental and biological factors including soil nutrients and diazotrophic community composition. Increased soil moisture availability generally promoted FLNF rates, but extreme rainfall events were detrimental. These climate-related responses suggest a potential for loss of FLNF-derived N contributions under projected climate shifts. We found a significant, but weak correlation between diazotrophic community composition and FLNF rates. We also observed a significant shift in the diazotrophic community composition between 2017 and 2018 and similarly measured a significant difference in FLNF rates between growing seasons. Lastly, we found that seasonal FLNF N contributions, based on measurement with high temporal resolution, has the potential to meet up to 80% of switchgrass N demands suggesting that FLNF measurements extrapolated from fewer time points or locations may underestimate these potential N contributions. © 2021 The Authors. GCB Bioenergy published by John Wiley & Sons Ltd.