The majority of mass of any plant is produced from water from the soil and carbon dioxide with sunlight from the air. 6 CO2 + 6 H2O + sunlight ---> C6H12O6 + 6 O2 ... The gluclose (C6H12O6) is a simple sugar that becomes the biomass of the plant. Other minor contributors to the mass are from fertilizers (mostly N, P, and K) and minerals.