Evaluation Of Rice Drought Stress Response Using Carbon Isotope Discrimination

In this study,three rice cultivars were grown in a pot experiment using plastic pots under four water levels in two planting patterns:plant pattern1?non-competitive?,three rice shoots of each cultivar were planted in a pot and plant pattern2?competitive?,one rice shoot of three cultivars were planted in a pot in 2014 and 2015.Dry weight accumulation,grain yield,gas exchange parameters,chlorophyll fluorescence parameters,proline,water soluble carbohydrate,WUE at each levels,?of topmost leaves at tillering,heading,maturity and?of topmost leaves,stems and grain yield at maturity were determined.The main results were as follows:1.DM and yield decreased with increasing severity of drought stress in both plant mode trails.WUE_wh and WUE_g increased under mild stress then decreased highly with further increasing severity of drought stress.Significant differences were found for DM,GY,WUE_whh and WUE_g between rice varieties under ecch water supply conditions.Changes in?were always consistent with changes in DM,GY,WUE_wh and WUEg under different water supply condition and for all genotypes,Qishanzhan>Akihikari>Bendao.And the extent of variation among genotypes for DM and yield was more significantly in plant mode2 trial than in plant mode1 trial.2.In both plant pattern trails,?decreased with increasing severity of drought stress and time.Significant differences were found for?between rice varieties under ecch water supply conditions.And the extent of variation among genotypes increased with increasing severity of drought stress and time.Rankings of genotypes for?at tillering,heading and maturity were generally consistent in each treatment for both plant pattern trails.Within each plant mode trail,the relationships between?of each sample stages of two years were highly significant?P?0.05;P?0.001?.The correlations between?measured at maturity was relatively stronger than other sampling stages.And the correlations between?of each sample stages were more significant under plant mode1 than these correlations under plant mode2.3.Photosynthesis rate?A?,the ratio of internal CO₂ concentration to ambient CO₂concentration?C_i/C_a?of rice cultivars decreased slightil under mild stress then decreased highly with further increasing severity of drought stress.Changes in?at maturity were always consistent with changes in DM,GY,WUE_wh and WUEg under well-watered,mild stress,moderate stress conditions and for all genotypes,Qishanzhan>Akihikari>Bendao.And significant differences were found for A,g_s,E and C_i/C_a between rice varieties.?at maturity was significantly associated with A,g_s,E and C_i/C_a in both two plant mode trials.4.The study of chlorophyll fluorescence parameters of leaves shown that,the value of Fv/Fm?Y?II??ETR and qP of rice cultivars decreased slightil under mild stress then decreased highly with further increasing severity of drought stress.the value of Fv/Fm?Y?II??qP and ETR of Qishanzhan were all larger than those of Akihikari and Bendao under water supply conditions at heading and filling.And the decrease margin of Fv/Fm?qP and ETR of Qishanzhan under different water stress conditions were bigger than Akihikari and Bendao,which were always consistent with changes in proline,water soluble carbohydrate.5.Proline,water soluble carbohydrate of Qishanzhan were all larger than those of Akihikari and Bendao under mild stress,moderate stress and severe stress at heading and filling.And the increase margin of proline,water soluble carbohydrate of Qishanzhan under different water stress conditions were bigger than Akihikari and Bendao.Drought resistance:Qishanzhan>Akihikari>Bendao.6.?measured at maturity was significantly associated with WUE_wh and WUE_g.The correlations between?_m and DM_t,DM_h,DM_m,GY were more significant than the correlations between?_t??_h and DM_t,DM_h,DM_m,GY in both two plant pattern trials.The correlations between?and DM?GY were more significant under mild stress,moderate stress conditions than these correlations under well-watered and severe stress conditions.?was more significant correlated with biomass and grain yield in each growth stages under plant mode2than with these parameters under plant mode1.Therefore,?of leaves at maturity might be better related to biomass,grain yield and WUE of rice under mild stress and moderate stress.