Photosynthesis, water use efficiency, and δ¹³C in two rice genotypes with contrasting response to water deficit

The effects of water deficit and re-irrigation were studied in glasshouse-grown rice plants (cvs. CimarrĂłn and Fonaiap 2000) which differ in their susceptibility to water deficit. Relative water content decreased from >90 to 67-69 % and recovered to pre-stress values within 24 h after re-irrigation. The irradiance-saturated rate of photosynthesis (P sat), transpiration rate (E), and stomatal conductance (g s) decreased with water deficit. E and g s decreased similarly in both cultivars, but P sat was more strongly inhibited in CimarrĂłn than in Fonaiap 2000. Water deficit increased water use efficiency (WUET) over 2-fold in Fonaiap 2000 and by 1.5-fold in CimarrĂłn. The ratio of intercellular to ambient CO2 concentration (C i/C a) decreased in Fonaiap 2000 during mild stress but increased at severe stress. Contrarily, CimarrĂłn did not change C i/C a with water deficit. After re-irrigation Fonaiap 2000 recovered P sat to ca. 80 % of control values 24 h after re-irrigation, whereas CimarrĂłn recovered to 60 % of control values 48 h after re-irrigation. E and g s recovered to a lesser extent (50 %) than P sat, after 48 h of re-irrigation in both cultivars. Total aboveground and green (live) biomass were unaffected by water deficit in Fonaiap 2000 but were reduced by 21 and 40 % in CimarrĂłn, respectively. Dead biomass increased in stressed plants of both cultivars but to a larger extent in CimarrĂłn than in Fonaiap 2000. Water deficit increased δ13C in Fonaiap 2000, whereas CimarrĂłn was unaffected by water deficit showing lower values than those of Fonaiap 2000. δ13C was highly and linearly correlated to the ratio C i/C a. WUET was also significantly correlated to δ13C.