A fundamental assumption in trait-based ecology is that relationships between traits and environmental conditions are globally consistent. We use field-quantified microclimate and soil data to explore if trait-environment relationships are generalisable across plant communities and spatial scales. We collected data from 6720 plots and 217 species across four distinct tundra regions from both hemispheres. We combine this data with over 76000 database trait records to relate local plant community trait composition to broad gradients of key environmental drivers: soil moisture, soil temperature, soil pH, and potential solar radiation. Results revealed strong, consistent trait-environment relationships across Arctic and Antarctic regions. This indicates that the detected relationships are transferable between tundra plant communities also when fine-scale environmental heterogeneity is accounted for, and that variation in local conditions heavily influences both structural and leaf economic traits. Our results strengthen the biological and mechanistic basis for climate change impact predictions of vulnerable high-latitude ecosystems. Kemppinen, Niittynen, le Roux, Momberg, Happonen, Aalto, Rautakoski, Enquist, Vandvik, Halbritter, Maitner & Luoto (2021). Consistent trait-environment relationships within and across tundra plant communities. Nature Ecology and Evolution These are the data and codes from Kemppinen et al. (2021).

JK was funded by the Doctoral Programme in Geosciences at the University of Helsinki, PN by the Kone Foundation, MM by the National Research Foundation via the SANAP programme, and KH by the Doctoral Programme in Wildlife Biology Research at the University of Helsinki. The field campaigns were funded by the Academy of Finland (project numbers 307761 and 286950) and the National Research Foundation's South African National Antarctic Program (unique grant numbers 93077 and 110726). We acknowledge the funding by the Finnish Ministry of Education and Culture (The FinCEAL Plus BRIDGES coordinated by the Finnish University Partnership for International Development).