As an indispensable environment element for crop growth, air temperature has brought challenge for the sustainable
development of rice ( Oryza sativa
L.) production. Elevated air temperature led to great loss in rice grain yield in many
districts suffering from heat stress due to the greenhouse effect worldwide, which has received more and more attention
from researchers. A field experiment was conducted to investigate impacts of high air temperature (HAT) after rice heading
stage on dynamics of SPAD values, soluble sugar, soluble protein, and malondialdehyde (MDA) contents of flag leaves, and
grain yield attributes. The results showed that HAT significantly reduced SPAD values, soluble sugar and protein contents,
seed-setting rate, number of filled grains per panicles, 1000-grain weight, and grain yield, while increased MDA content.
There exists strong correlation between each physiological parameter and days from heading stage to maturity, which
can be simulated by quadratic curve equation or linear regression equation. Under HAT, the enhanced MDA content and
decreased soluble sugar content demonstrated the damage of membrane structure and photosynthesis function of rice flag
leaves, which was partially attributed to the reduced SPAD value and soluble protein content. In the present experiment,
rice seed-setting rate was more vulnerable to HAT than grain weight. The disturbance of physiological metabolism in flag
leaves was a fundamental reason for the reduction of rice grain yield under HAT.