Nitrogen fertilizer has opened the door to ensure food security by enabling large cropping yields, but it has been detrimental to ecosystems across multiple scales. Long-term utilization of mineral (ammonium and nitrate) fertilizer can erode the mutualistic relationship that exists between nitrogen-fixing rhizobia and its leguminous host plant species. Rhizobia relies on the carbon substrates received as dicarboxylate acids from the host to reduce atmospheric nitrogen to ammonia or ammonium. The availability of ammonium and ammonia is critical for nitrogen fixation; it is the entering of energy into all ecosystems and the first step of nitrogen cycling. GEMS trainee Natalie Belloso will investigate rhizobia’s metabolic function across strains that have evolved under different nitrogen conditions using a substrate-specific metabolic test which can elucidate what biogeochemical transformations are occurring.