Effects of High Temperature Stress in Different Periods on Dry Matter Production and Grain Yield of Summer Maize

Frequent, recurrent and prolonged high temperature stress had significant effects on grain yield of summer maize in Huang-Huai-Hai region. In this study, we investigated the effects of high temperature stress at the V12 stage and VT stage on leaf photosynthetic characteristics, carbon assimilate accumulation, distribution and grain yield of maize varieties with different heat tolerance.

In this study, heat resistant maize variety Zhengdan 958 (ZD958) and heat sensitive maize variety Xianyu 335 (XY335) were used as materials. The normal temperature treatments (day 32℃12 h /night 22℃12 h) were set as the control at the same time. High temperature greenhouse equipped with automatic temperature and humidity control facilities was used to simulate the effect of natural field high temperature, the high temperature stress treatments (day 38℃12 h/night 28℃12 h) were set at V12 and VT stage, respectively. The dynamic characteristics of leaf area index (LAI), carbon metabolism enzyme activities, photosynthetic rate and carbon assimilate accumulation and allocation were compared after high temperature stress, aimed to determine the response mechanism of dry matter production performance and grain yield to high temperature stress.

After high temperature stress, LAI, carbon metabolism enzyme activities, net photosynthetic rate and dry matter accumulation of two cultivars were significantly decreased. LAI, RuBP carboxylase activity, PEP carboxylase activity, net photosynthetic rate and dry matter accumulation of ZD958 and XY335 decreased by 2.98%-4.21%, 40.38%-54.46%, 16.88%-30.60%, 18.14%-25.49%, 12.83%-19.38% and 3.80%-5.07%, 56.56%-76.16%, 26.33%-33.66%, 22.37%-34.62%, 22.07%-26.72%, respectively. The decrease range of high temperature stress in VT stage was larger than that in V12 stage. After high temperature stress, transpiration rate of summer maize leaves increased, while leaf water use efficiency decreased significantly. Under high temperature stress, ¹³C assimilation of ZD958 and XY335 decreased by 18.48% and 22.82%, respectively, and the proportion of ¹³C assimilation in grains decreased. The high temperature stress significantly decreased grain number per spike and grain yield, although 1000 grain weight increased slightly. Compared to the optimum temperature, after V12 high temperature stress, the grain number per spike and yield of ZD958 decreased by 62.53% and 45.87%. After VT high temperature stress, grain number per spike and yield decreased by 70.53% and 66.89%. After V12 high temperature stress, the grain number per spike and yield of XY335 decreased by 70.50% and 62.87%. After VT high temperature stress, grain number per spike and yield decreased by 85.41% and 80.61%. The decrease range of high temperature stress in VT stage was larger than that in V12 stage, and XY335 decreased more than ZD958.

The high temperature stress reduced LAI, RuBP carboxylase and PEP carboxylase activities, and significantly reduced photosynthetic rate and dry matter production performance of summer maize. Under high temperature stress, the grain number per spike decreased significantly, which inhibited the transportation of carbohydrate from leaf and stem to grain, resulting in lower grain yield. The effects of high temperature stress on dry matter performance and grain yield of summer maize in VT stage was significantly greater than that in V12 stage. The decrease of heat sensitive variety XY335 was significantly greater than that of heat resistant variety ZD958 in two periods.