Inference NOT supported by CO₂ and N-fixation study:
Elevated carbon dioxide may initially stimulate photosynthesis and provide more carbon to nitrogen-fixing symbioses, but sustained responses can weaken when micronutrients become limiting. Nitrogenase and associated enzymes require iron and molybdenum, so lower leaf concentrations can constrain fixation over time. An inference that carbon dioxide enhances micronutrient uptake runs opposite to such evidence and is therefore unsupported. Increased biomass can instead dilute mineral concentrations even when total uptake changes little. Net primary production equals gross primary production minus plant respiration and represents biomass or energy made available for growth and consumers. Rates must be compared on the same area, biomass, leaf-area, and time basis because changing the denominator can reverse an apparent ecosystem ranking. Climate, nutrients, disturbance, species traits, and food-web structure interact, so broad ecological generalisations describe tendencies rather than universal rules. Energy is lost as metabolic heat at every trophic transfer, while elements such as nitrogen and phosphorus are recycled through organisms and the physical environment.
Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 17-19