2023-03-292023-03-292022Dong, N., Wright, I.J., Chen, J.M., Luo, X., Wang, H., Keenan, T.F., Smith, N.G., & Prentice, I.C.. 2022. Rising CO2 and warming reduce global canopy demand for nitrogen. New Phytologist, 235(5). https://doi.org/10.1111/nph.18076https://doi.org/10.1111/nph.18076https://hdl.handle.net/2346/92047© 2022 The Authors. New Phytologist © 2022 New Phytologist Foundation. cc-by-nc-ndNitrogen (N) limitation has been considered as a constraint on terrestrial carbon uptake in response to rising CO2 and climate change. By extension, it has been suggested that declining carboxylation capacity (Vcmax) and leaf N content in enhanced-CO2 experiments and satellite records signify increasing N limitation of primary production. We predicted Vcmax using the coordination hypothesis and estimated changes in leaf-level photosynthetic N for 1982–2016 assuming proportionality with leaf-level Vcmax at 25°C. The whole-canopy photosynthetic N was derived using satellite-based leaf area index (LAI) data and an empirical extinction coefficient for Vcmax, and converted to annual N demand using estimated leaf turnover times. The predicted spatial pattern of Vcmax shares key features with an independent reconstruction from remotely sensed leaf chlorophyll content. Predicted leaf photosynthetic N declined by 0.27% yr−1, while observed leaf (total) N declined by 0.2–0.25% yr−1. Predicted global canopy N (and N demand) declined from 1996 onwards, despite increasing LAI. Leaf-level responses to rising CO2, and to a lesser extent temperature, may have reduced the canopy requirement for N by more than rising LAI has increased it. This finding provides an alternative explanation for declining leaf N that does not depend on increasing N limitation.engacclimationCO2fertilizationcoordination hypothesisleaf chlorophyllnitrogen cyclenitrogen demandphotosynthetic capacityremote sensingArticle