Roots are affected by the aerial environment of the crop. Root growth and distribution in cotton (Gossypium hirsutum L.) were examined under various aerial temperatures and CO₂ concentrations. Plants were grown in controlled environment chambers that had a plexiglas top for growing plants under nearly natural daylight and a soil bin filled with a sand:vermiculite mixture (3:1 by volume). The soil bin had one glass side for making root observations. Day/night temperatures were controlled at 15/7, 20/12, 25/17, 30/22, and 35/27 C averaging 17.8, 18.7, 22.7, 26.6, and 30.6 C over the period of growth. CO₂ concentration were 350 and 700 µL L^-1 for each CO₂ concentrations were temperature. At least once each week, new root length appearing at the glass face of the soil bin was measured and then marked with a wax pencil. The number of growing root tips and the depth of the root system were also recorded. After the final destructive harvest at 70 days after emergence, the rooting medium in the soil bins was removed layer by layer, the roots washed out, dried and weighed.

Roots penetrated into the soil profile faster at higher temperatures but were not affected by [CO₂]. Roots were fairly evenly distributed over the top 60 cm of the soil profile in the higher [CO₂] treatment but roots in the lower [CO₂] treatment were more localized in the top 20cm of soil and at a 51-60 cm depth. Root elongation rate increased linearly with increased temperature at the higher (CO₂]. At the lower [CO₂], root elongation rate did not increase beyond 26.6 C. Root activity began to increase at 30 days after emergence (DAE) at all [CO₂] and temperatures except 17.8 C. Root activity was depressed in all temperature and [CO₂] treatments at 42 DAE when plants were initiating flower buds (squaring), and again after 63 days when fruits (bolls) were developing. There was no effect on root weight at the various temperatures except at 30.6 C where there was significantly more root weight at higher [CO₂]. This increased root weight was not a result of increased root elongation, suggesting that the root was acting as a storage organ. Root growth and penetration into the soil profile increased with increased temperature over the range studied. The higher [CO₂] produced a more uniform root distribution throughout the soil profile than the lower [CO₂] and increased root dry weight in the 30.6 C treatment.