Johann Baptista van Helmont introduced the process called
John Woodward concluded that plants need water and that soil is essential to the weight of a plant.
Stephen Hales suggested that plants retrieve something from the atmosphere to survive.
Charles Bonnet found a way of measuring the rates of photosynthesis and found that when leaves are in water they release bubbles.
Joseph Black was the first to discover carbon dioxide and and latent/specific heat.
Joseph Priestley had a theory relating to combustion which turned out incorrect but did pave the way to photosynthesis concepts today.