Fan, YuzhenNoble, Daniel W.A.Medlyn, Belinda E.Monson, Russell K.Sage, Rowan F.Smith, Nicholas G.Ainsworth, Elizabeth A.Busch, Florian A.Danila, Florence R.Ermakova, MariaFriesen, PatrickFurbank, Robert T.Gan, Shu HanGhannoum, OulaGriffith, Daniel M.Gu, LianhongJacob, VinodKnauer, JürgenLeakey, Andrew D.B.Li, ShuaiLombardozzi, Danica L.Ludwig, MarthaPathare, Varsha S.Peixoto, Murilo M.Prado, KarineSonawane, Balasaheb V.Still, Christopher J.von Caemmerer, SusanneWoodford, RussellWay, Danielle A.2026-01-022026-01-020028-646XPubMed:40887880ORCID:/0000-0003-4801-5319/work/195850466ORCID:/0000-0003-1857-9244/work/195850950ORCID:/0000-0001-9460-8743/work/195852359ORCID:/0000-0002-7352-3852/work/195855691https://hdl.handle.net/1885/733802633Our understanding of how photosynthetic capacity varies among C4 species and across growth and measurement conditions remains limited. We collated 1696 CO2 response curves of net CO2 assimilation rate (A/Ci curves) from C4 species grown and measured at various environmental conditions and used these data to estimate the apparent maximum carboxylation activity of phosphoenolpyruvate carboxylase (VpmaxA) and CO2-saturated net photosynthetic rate (Amax), two key parameters describing photosynthetic capacity. We examined how VpmaxA and Amax vary with species-specific traits, growth and measurement conditions. We found little systematic variation of VpmaxA and Amax across the classical C4 biochemical subtypes or growth forms, but showed that growth temperature and measurement conditions are major factors determining C4 photosynthetic capacity. We found no evidence that common C4 model species (e.g. maize, sorghum and Setaria viridis) differ in photosynthetic capacity from other C4 species when grown in controlled environments. However, C4 model species showed up to twice the photosynthetic capacity of other C4 species when grown in the field. Our multivariate model accounts for 47–51% of the variation reported in VpmaxA and Amax, and we argue that environmental conditions have a greater influence on C4 photosynthetic capacity than biochemical subtypes or growth forms.This work was conducted as part of the C4 Photosynthesis Working Group supported by the John Wesley Powell Center for Analysis and Synthesis, funded by the US Geological Survey (award no.: 20-07-0232). Additional support for DAW came from the Australian National University Futures Scheme, and for YF from an Australian Research Council Discovery Project (DP230103122). DWAN was supported by an Australian Research Council Future Fellowship (FT220100276). BEM was supported by an Australian Research Council Laureate Fellowship (FL190100003). ADBL was supported by the DOE Center for Advanced Bioenergy and Bioproducts Innovation (US Department of Energy, Office of Science, Biological and Environmental Research Program under award no.: DE-SC0018420). FAB was supported by the Natural Environment Research Council (NE/W00674X/1). KP was supported by US National Science Foundation grants (IOS-2312181, IOS-2406533, IOS-1546838, MCB-1617020, DBI-2213983 and OISE-2434687), US Department of Energy, Office of Science, Office of Biological and Environmental Research, Genomic Science Program grants (DE-SC0018277, DE-SC0020366, DE-SC0023160, DE-SC0021286 and DE-SC0008769) and Carnegie Science Venture Grant (10908). ML was supported by an Australian Research Council Discovery Project (DP180102747). Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government. Open access publishing facilitated by Australian National University, as part of the Wiley - Australian National University agreement via the Council of Australian University Librarians. This work was conducted as part of the C Photosynthesis Working Group supported by the John Wesley Powell Center for Analysis and Synthesis, funded by the US Geological Survey (award no.: 20‐07‐0232). Additional support for DAW came from the Australian National University Futures Scheme, and for YF from an Australian Research Council Discovery Project (DP230103122). DWAN was supported by an Australian Research Council Future Fellowship (FT220100276). BEM was supported by an Australian Research Council Laureate Fellowship (FL190100003). ADBL was supported by the DOE Center for Advanced Bioenergy and Bioproducts Innovation (US Department of Energy, Office of Science, Biological and Environmental Research Program under award no.: DE‐SC0018420). FAB was supported by the Natural Environment Research Council (NE/W00674X/1). KP was supported by US National Science Foundation grants (IOS‐2312181, IOS‐2406533, IOS‐1546838, MCB‐1617020, DBI‐2213983 and OISE‐2434687), US Department of Energy, Office of Science, Office of Biological and Environmental Research, Genomic Science Program grants (DE‐SC0018277, DE‐SC0020366, DE‐SC0023160, DE‐SC0021286 and DE‐SC0008769) and Carnegie Science Venture Grant (10908). ML was supported by an Australian Research Council Discovery Project (DP180102747). Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government. Open access publishing facilitated by Australian National University, as part of the Wiley ‐ Australian National University agreement via the Council of Australian University Librarians. 420enPublisher Copyright: © 2025 The Author(s). New Phytologist © 2025 New Phytologist Foundation.A/C curveC biochemical subtypeC photosynthesisenvironmental responsephotosynthesis modelling202510.1111/nph.70525105014745222