Elevated atmospheric CO2 improved Sorghum plant water status by ameliorating the adverse effects of drought

. The interactive effects of atmospheric CO2 concentration and soil-water c ontent on grain sorghum (Sorghum bicolor) are reported here. . Sorghum plants were exposed to ambient (control) and free-air CO2 enrichm ent (FACE; ambient + 200 mu mol mol(-1)), under ample (wet, 100% replacemen t of evapotranspiration) and reduced (dry, postplanting and mid-season irri gations) water supply over two growing seasons. . FACE reduced seasonal average stomatal conductance (g(s)) by 0.17 mol (H2 O) m(-2) s(-1) (32% and 37% for dry and wet, respectively) compared with co ntrol; this was similar to the difference between dry and wet treatments. F ACE increased net assimilation rate (A) by 4.77 mu mol (CO2) m(-2) s(-1) (2 3% and 9% for dry and wet, respectively), whereas dry decreased A by 10.50 mu mol (CO2) m(-2) s(-1) (26%) compared with wet. Total plant water potenti al (psi (W)) was 0.16 MPa (9%) and 0.04 MPa(3%) less negative in FACE than in the control treatment for dry and wet, respectively. Under dry, FACE sti mulated final shoot biomass by 15%. . . By ameliorating the adverse effects of drought, elevated atmospheric CO2 improved plant water status, which indirectly caused an increase in carbon gain.