The data consists of plant physiological measurements from 15 sites located in the Conwy catchment (North Wales) and from 2 sites in North West England. Plant photosynthetic parameters for the maximum rate of carboxylation (Vcmax), the maximum rate of electron transport (Jmax) and the maximum light saturated photosynthesis (Asat) were measured on the dominant plant species as were foliar nitrogen (Foliar N) and phosphorus (Foliar P). Leaf mass area (LMA) and specific leaf area (SLA) were recorded on the same leaves. Data were collected in 2013, 2014 and 2016. The sites were chosen to represent habitat types and the terrestrial productivity gradient in Britain from intensive agriculturally managed lowland grasslands through to montane heath. Plots within the sites were located using a stratified random sampling design. Plant parameters were tested across a land use intensification gradient to detect parameters that can predict aboveground biomass production across different land management types. Data were used to enhance the predictions of biomass production in the Joint UK Land Environment Simulator model (JULES). Measurements informed the improvement of the nitrogen cycle component in the model. Measurements were undertaken by trained members of staff from Bangor University, the Centre for Ecology & Hydrology and Exeter University. This data was collected for the NERC project 'The Multi-Scale Response of Water quality, Biodiversity and Carbon Sequestration to Coupled Macronutrient Cycling from Source to Sea' (NE/J011991/1). The project is also referred to as Turf2Surf.