Legumes are different: Leaf nitrogen, photosynthesis, and water use efficiency

Mark Andrew Adams (Lead / Corresponding author), Tarryn L. Turnbull, Janet I. Sprent, Nina Buchmann

Research output: Contribution to journalArticlepeer-review

173 Citations (Scopus)
215 Downloads (Pure)


Using robust, pairwise comparisons and a global dataset, we show that nitrogen concentration per unit leaf mass for nitrogen-fixing plants (N2FP; mainly legumes plus some actinorhizal species) in nonagricultural ecosystems is universally greater (43-100%) than that for other plants (OP). This difference is maintained across Koppen climate zones and growth forms and strongest in the wet tropics and within deciduous angiosperms. N2FP mostly show a similar advantage over OP in nitrogen per leaf area (Narea), even in arid climates, despite diazotrophy being sensitive to drought. We also show that, for most N2FP, carbon fixation by photosynthesis (Asat) and stomatal conductance (gs) are not related to Narea-in distinct challenge to current theories that place the leaf nitrogen-Asat relationship at the center of explanations of plant fitness and competitive ability. Among N2FP, only forbs displayed an Narea-gs relationship similar to that for OP, whereas intrinsic water use efficiency (WUEi; Asat/gs) was positively related to Narea for woody N2FP. Enhanced foliar nitrogen (relative to OP) contributes strongly to other evolutionarily advantageous attributes of legumes, such as seed nitrogen and herbivore defense. These alternate explanations of clear differences in leaf N between N2FP and OP have significant implications (e.g., for global models of carbon fluxes based on relationships between leaf N and Asat). Combined, greater WUE and leaf nitrogen-in a variety of forms-enhance fitness and survival of genomes of N2FP, particularly in arid and semiarid climates.

Original languageEnglish
Pages (from-to)4098-4103
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number15
Early online date30 Mar 2016
Publication statusPublished - 12 Apr 2016


  • Actinorhizal species
  • Legume
  • Nitrogen
  • Photosynthesis
  • Water use efficiency

ASJC Scopus subject areas

  • General


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