title: Despite phylogenetic effects, C3-C4 lineages bridge the ecological gap to C4 photosynthesis.
abstract: C4photosynthesis is a physiological innovation involving several anatomical and biochemical components that emerged recurrently in flowering plants. This complex trait evolved via a series of physiological intermediates, broadly termed 'C3-C4', which have been widely studied to understand C4origins. While this research program has focused on biochemistry, physiology, and anatomy, the ecology of these intermediates remains largely unexplored. Here, we use global occurrence data and local habitat descriptions to characterize the niches of multiple C3-C4lineages, as well as their close C3and C4relatives. While C3-C4taxa tend to occur in warm climates, their abiotic niches are spread along other dimensions, making it impossible to define a universal C3-C4niche. Phylogeny-based comparisons suggest that, despite shifts associated with photosynthetic types, the precipitation component of the C3-C4niche is particularly lineage specific, being highly correlated with that of closely related C3and C4taxa. Our large-scale analyses suggest that C3-C4lineages converged toward warm habitats, which may have facilitated the transition to C4photosynthesis, effectively bridging the ecological gap between C3and C4plants. The intermediates retained some precipitation aspects of their C3ancestors' habitat, and likely transmitted them to their C4descendants, contributing to the diversity among C4lineages seen today.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK marjorie.lundgren@sheffield.ac.uk.
authors.forename: Marjorie R
authors.identifier: 0000-0002-2489-3646
authors.initials: MR
authors.lastname: Lundgren
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
authors.forename: Pascal-Antoine
authors.identifier: 0000-0001-6292-8734
authors.initials: PA
authors.lastname: Christin
mesh_terms: D017753:Ecosystem; D005843:Geography; D010788:Photosynthesis; D010802:Phylogeny; D010944:Plants / Q000235:genetics* / Q000378:metabolism
keywords: Biomes; C3–C4 intermediate; C4 photosynthesis; ecology; evolution; phylogeny.