A framework for scaling symbiotic nitrogen fixation using the most widespread nitrogen fixer in eastern deciduous forests of the United States

Carbon uptake by the terrestrial biosphere depends on supplies of new nitrogen (N) from symbiotic N fixation, but we lack a framework for scaling fixation accurately and predicting its response to global change. We scaled individual fixers (i.e. plants that host N-fixing bacteria), quantifying three key parameters—the abundance fixers, whether they are fixing their rates. apply this black locust, widespread tree in temperate forests eastern United States, harness long-term data southern Appalachian scale trees landscape over succession. Symbiotic at peaked first decade following forest disturbance, then declined. This pattern was due declining density rates locust Independent succession, coincident with chronic atmospheric deposition, have evidence suggesting nodule biomass produced has declined 83% last decades. difference translates maximum rate 11 kg ha?1 year?1 average 1.5 contemporary forests. Synthesis. find controls space time, lower deciduous than previous estimates. Our can be applied other aid predictions ecosystem