Light Response Characteristics of Summer Maize at Different Growth Stages Under Drought

The field experiment of drought on summer maize growth is carried out by using large electric water proof and irrigation installations. First of all, the diurnal variations of photosynthesis and photosynthesis-light response curves of summer maize leaves are measured. And then, the different models are used to fit light response curve to determine the optimal model and extract the photosynthetic parameters. Finally, the impact of soil moisture on the photosynthetic characteristics of summer maize leaves at different growth stages is discussed. The comparison of light response curve fitting by different models shows that comparing to the non-rectangular hyperbolic model and exponential model, the simulation result of modified rectangular hyperbola model is better. In particular, it can effectively simulate the downward trend of light saturated net photosynthetic rate with light intensity increased, which is more common under drought conditions. In addition, the use of modified rectangular hyperbola model can extract the quantum efficiency of the light compensation point which is the numerical uniqueness indicator of evaluation of crop light use. The photosynthetic parameter analysis shows that both light saturation point (LSP) and maximum net photosynthetic rate (P_max) decline in different growth stages, and quantum efficiency of light compensation point (CQY) and light compensation point (LCP) are insignificantly affected under slight drought. With the aggravation of drought, LSP and P_max has a further decrease and CQY has a significant decline while LCP had a great increase under severe drought condition. The comparison of different growth stages show that LSP and P_max decline largest in jointing stage, second in tasselling stage and least in milky maturity stage under slight drought. LSP and P_max decrease by 24.1% to 43.7% and 9.3% to 46.1%. LSP and P_max decline largest in tasselling stage, the second in milky maturity stage, the least in jointing stage under severe drought. LSP and P_max decrease by 12.3% to 33.6% and 48.5% to 62.2%. In addition, observations show that photosynthetic and transpiration rate of summer maize leaves at different growth stages both decline under drought. The comparison of different growth stages show that photosynthetic and transpiration decline largest in tasselling stage, second in jointing stage and least in milky maturity stage under slight drought. With the aggravation of drought, photosynthetic and transpiration still decline largest in tasselling stage, but second in milky maturity stage, and least in jointing stage. Water use efficiency of maize leaves at different growth stages are relatively large under suitable soil water condition (2.8—4.5 μmol·mmol^-1), and slight drought (2.6—4.2 μmol·mmol^-1). Relative to tasselling and milky maturity stage, water use efficiency of maize leaves in jointing stage is the largest.