The role of spectral quality and CO2 concentration in environmental control of lignin synthesis in spring wheat is being studied by the NASA Controlled Ecological Life Support System Program (CELSS). Wheat cultivars were exposed to four different spectral environments provided by 1) metal halide lamps (MH), 2) high pressure sodium lamps (HPS), 3) low pressure sodium lamps (LPS; almost monochromatic, 589 nm), or 4) LPS plus low irradiance blue light (5 μmol m-2 s-1; LPS + Blue) at equal photosynthetic photon flux. Stem lignin content was suppressed 25% under the LPS compared with the MH and HPS; blue addition (LPS + Blue) resulted in 25% greater lignin content compared with the LPS alone and 8% suppression compared with MH and HPS. CO2 studies compared lignin content of wheat grown in the field, greenhouse at 350 μmol mol-1 CO2, and growth chambers at 350 and 700 μmol mol-1 CO2, Lignin content was greatest and equal in the field and growth chamber at 700 μmol mol-1 CO2. Lowest lignin content was measured in the growth chamber at 350 μmol mol-1 CO2; lignin content in the greenhouse was intermediate between that measured in the field and growth chamber at 350 μmol mol-1 CO2, Additional CO2 studies in controlled environments will be discussed.