Evidence of enzyme-level thermal constraint on biological nitrogen fixation rates across systems and scales

Abstract

Biological nitrogen fixation (BNF) provides half of global new nitrogen annually and plays an important role in biodiversity patterns and global biological carbon uptake processes. BNF rates accelerate with warming, with known implications for ecological functioning, yet the strength of this temperature sensitivity and its context dependence are not well understood. Here we synthesized 70 controlled experimental tests of the acute temperature dependence of nitrogen fixation rates and found that BNF rates accelerate with temperature in a consistent way across levels of biological organization from enzyme to community, mirroring scaling of metabolic temperature dependence across levels of organization for respiration, photosynthesis and methane production. This BNF temperature dependence is also remarkably consistent across biological systems. This analysis shows multiple lines of evidence for general, scalable effects of temperature on nitrogen fixation rates, in line with previous suggestions of a strong enzyme-level constraint. This widespread pattern may be important for understanding effects of warming on coupled carbon-nitrogen systems with ongoing global change.