Diurnal Variation And Directivity Of Photosynthetic Carbon Metabolism In Maize Hybrids Under Drought Stress

In order to further improve the evaluation index system of maize varieties,the maize photosynthetic response characteristics and the photosynthetic carbon metabolism characteristics between different hybrids under drought stress were analyzed based on the differences of photosynthetic rate, starch, sucrose and other physiological and biochemical indexe, come up with related enzyme activities in diurnal variation under gradient soil drought stress. The main research results are as follows:1. The maize photosynthesis presented unimodal trends without "noon break" phenomenon in the daily cycle, the peak decreased and appeared in advance as result of drought stress, mild, moderate and severe drought stress decreased the accumulation of photosynthetic peak between 9:00 and 15:00 hours daily by 25%、50% and 70% compared with high moisture transaction; The photosynthetic accumulate in the early stage of between 6:00 and 9:00 hours daily decreased with the deterioration of the drought degree, but differed among species and were unstable. The ratio of photosynthetic accumulation between morning and afternoon was less than 1.2 under the condition of sufficientwater supply and significantly increased with the increase of stress level. That indicated that the photosynthesis in the afternoon was strongly influenced by drought stress and the decrease of the photosynthetic accumulation ratio between morning and afternoon is important for high photosynthetic efficiency in breeding. Nongda108 can maintain the low and stable level of these indicators among multiple treatments, and also keep strong ability of photosynthetic production under stress.2. Carbon flux from day to night is important for normal physiological metabolism of plants. The sucrose,starch concentration variation characteristics in corn leaves and stalks pesented unimodal curve in a day, leaf sucrose content peak appeared earlier than starch but peak was lower than that of starch, the performance of stalk consistented with the leaf; The starch content decreased with stress aggravated but the sucrose content was stable compared with sucrose, starch concentration of photosynthetic peak among drought treatments.3. The improvement values of corn leaf sucrose and starch concentration and the ratio between theirs in the early stage of photosynthesis were builded relationships with photosynthetic accumulation respectively, the contribution of unit photosynthetic rate to sucrose and starch was gotten. The contribution of unit photosynthetic rate to sucrose of Nongda108 and ND66 was high and stable, so Nongda108 and ND66 has the advantage of starch accumulation; the contribution of unit photosynthetic rate to sucrose/starch of Xianyu335 was at a higher level, so Xianyu335 benefits sucrose accumulation. The contribution of photosynthetic rate to sucrose/starch could be a classification standard as maize photosynthetic carbon metabolism. The variety benefiting sucrose accumulation like Xianyu335 has good yield potential and the variety benefiting starch accumulation like Nongda108 has the advantage of stress resistance and yield stability.4. Based on the metabolic biased, SPS and AGPase had no regular differences both in drought stress treatment and varieties comparison, the determination was complex, which were not recommended as auxiliary index; F2,6BP and monosaccharide content with glucose, fructose amount as a representative showed significantly reduced and increasd trend under stress condition, respectively,but the difference in comparison between varieties was small and unstable, needed for further research into the evaluation criteria.5. Leaf-air temperature difference (LATD) would be an effective index to measure maize plant moisture status. LATD was stable at the treatment of adequate soil water supply, mostly in the range of -4.0～-1.0℃. An increasing trend was observed following soil drying in LATD. The difference of LATD was up to 5℃ between the treatments of severe stress and adequate water supply, which occurred at 12:00 to 16:00 in a day. Diurnal variation of LTD presented a single peak curve and the peak value increased with the drought stress enhancing. Under drought stress, LATD was more significantly correlated with photosynthetically active radiation (PAR) and free-air temperature (Ta)than relative air humidity (RH) and vapor pressure deficit (VPD). In contrast to LATD, there was significant difference in LTD among hybrids, but the performance was difference for a hybrid at different determined time or stage. In conclusion, our results indicated that gradient soil drought stress could increase LATD and LTD step-by-step. LATD could reflect effectively the plant water status, but more studies should be carried out for the LTD used as a reliable indicator in selecting drought resistant variety in maize.