Nitrogen use strategy drives interspecific differences in plant photosynthetic CO 2 acclimation.

Rising atmospheric CO 2 concentration triggers an emergent phenomenon called plant photosynthetic acclimation to elevated CO 2 (PAC). PAC is often characterized by a reduction in leaf photosynthetic capacity (A sat ), which varies dramatically along the continuum of plant phylogeny. However, it remains unclear whether the mechanisms responsible for PAC are also different across plant phylogeny, especially between gymnosperms and angiosperms. Here, by compiling a dataset of 73 species, we found that although leaf A sat increased significantly from gymnosperms to angiosperms, there was no phylogenetic signal in the PAC magnitude along the phylogenetic continuum. Physio-morphologically, leaf nitrogen concentration (N m ), photosynthetic nitrogen-use efficiency (PNUE), and leaf mass per area (LMA) dominated PAC for 36, 29, and 8 species, respectively. However, there was no apparent difference in PAC mechanisms across major evolutionary clades, with 75% of gymnosperms and 92% of angiosperms regulated by the combination of N m and PNUE. There was a trade-off between N m and PNUE in driving PAC across species, and PNUE dominated the long-term changes and inter-specific differences in A sat under elevated CO 2 . These findings indicate that nitrogen-use strategy drives the acclimation of leaf photosynthetic capacity to elevated CO 2 across terrestrial plant species.