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Keywords:

  • C3 photosynthesis;
  • C4 photosynthesis;
  • gas exchange;
  • grasses;
  • growth analysis;
  • leaf nitrogen;
  • stomatal conductance;
  • water-use efficiency

Summary

  • Experimental evidence demonstrates a higher efficiency of water and nitrogen use in C4 compared with C3 plants, which is hypothesized to drive differences in biomass allocation between C3 and C4 species. However, recent work shows that contrasts between C3 and C4 grasses may be misinterpreted without phylogenetic control.
  • Here, we compared leaf physiology and growth in multiple lineages of C3 and C4 grasses sampled from a monophyletic clade, and asked the following question: which ecophysiological traits differ consistently between photosynthetic types, and which vary among lineages?
  • C4 species had lower stomatal conductance and water potential deficits, and higher water-use efficiency than C3 species. Photosynthesis and nitrogen-use efficiency were also greater in C4 species, varying markedly between clades. Contrary to previous studies, leaf nitrogen concentration was similar in C4 and C3 types. Canopy mass and area were greater, and root mass smaller, in the tribe Paniceae than in most other lineages. The size of this phylogenetic effect on biomass partitioning was greater in the C4 NADP-me species than in species of other types.
  • Our results show that the phylogenetic diversity underlying C4 photosynthesis is critical to understanding its functional consequences. Phylogenetic bias is therefore a crucial factor to be considered when comparing the ecophysiology of C3 and C4 species.