Ozone pollution effects on gas exchange, growth and biomass yield of salinity-treated winter wheat cultivars

A sand-culture experiment was conducted in four Open-Top-Chambers to assess the effects of O₃ on salinity-treated winter wheat. Two winter wheat cultivars, salt-tolerant Dekang961 and salt-sensitive Lumai15, were grown under saline (100mM NaCl) and/or O₃ (80±5nmolmol^-1) conditions for 35days. Significant (P<0.05) O₃-induced decreases were noted for both cultivars in terms of gas exchange, relative water content, growth and biomass yield in the no-salinity treatment. Significant (P<0.01) corresponding decreases were measured in Dekang961 but not in Lumai15 in the salinity treatment. Soluble sugar and proline contents significantly increased in both cultivars in combined salinity and O₃ exposure. O₃-induced down-regulation in the gradients of A-C_i and A-PPFD response curves were much larger in Dekang961 than in Lumai15 under saline conditions. Significant (P<0.05) interactions were noted in both salinity×cultivars and salinity×O₃ stresses. The results clearly demonstrated that O₃ injuries were closely correlated with plant stomatal conductance (g_s); the salt-tolerant wheat cultivar might be damaged more severely than the salt-sensitive cultivar by O₃ due to its higher g_s in saline conditions.