John Evans is a plant physiologist who has specialised in quantitatively linking biochemical and anatomical properties to the performance of leaves and plants. Photosynthesis research has been the focus throughout his career. His research has made significant impacts in three areas: 
1. Relating photosynthesis to nitrogen, 
2. Quantifying the conductance to CO2 diffusion within leaves 
3. Analysing how plants acclimate to their light environment.
He has examined how nitrogen is partitioned between various photosynthetic proteins, how their distribution through leaves interacts with the distribution of light and CO2 diffusion within leaves. He is interested in how rising atmospheric CO2 interacts with nitrogen cycling, with particular reference to symbiotic N2 fixation.