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

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Author for correspondence: Gerard W. Wall Tel: +1 602 437 1702 ext. 279 Fax: +1 602 437 5291 Email: gwall@uswcl.ars.ag.gov

Summary

  • • The interactive effects of atmospheric CO2 concentration and soil-water content on grain sorghum (Sorghum bicolor) are reported here.
  • • Sorghum plants were exposed to ambient (control) and free-air CO2 enrichment (FACE; ambient + 200 µmol mol−1), under ample (wet, 100% replacement of evapotranspiration) and reduced (dry, postplanting and mid-season irrigations) water supply over two growing seasons.
  • • FACE reduced seasonal average stomatal conductance (gs) by 0.17 mol (H2O) m−2 s−1 (32% and 37% for dry and wet, respectively) compared with control; this was similar to the difference between dry and wet treatments. FACE increased net assimilation rate (A) by 4.77 µmol (CO2) m−2 s−1 (23% and 9% for dry and wet, respectively), whereas dry decreased A by 10.50 µmol (CO2) m−2 s−1 (26%) compared with wet. Total plant water potential (ψw) 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 stimulated 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.

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