Effects of long term CO/sub 2/ concentration on field grown crops and trees

During the 1980 growing season four plant species, corn, soybean, loblolly pine, and sweetgum were exposed for 3 months to various CO/sub 2/ levels. Exposure of plants growing in 18 l pots took place in the field. Test atmospheres of CO/sub 2/ at 340, 520, 718, and 910 ppM were generated in transparent open top cylinders ventilated about 1.06 m/sup 3//sec. Pure CO/sub 2/ from a 14-ton liquid receiver was continuously injected into the ventilation air stream to generate the three elevated treatments. All treatments were replicated three times, and ambient treatments with and without chambers were established. Growth enhancement was observed in all four species. Decreased stomatal conductace with increasing CO/sub 2/ concentration was documented in corn, soybean, and sweetgum (pine was not measured). Net CO/sub 2/ uptake increased with increasing CO/sub 2/ in soybean and sweetgum, but remained constant or slightly decreased in corn. Gross photosynthesis also increased in soybean, but remained nearly constant or slightly increased in corn. Nitrogen fixation increased and accumulation of nitrogen was assessed. Changes in anatomy were observed. All data presented are for one late growing season in Raleigh, NC.