High sensitivity to climate change has been demonstrated in global maize production, especially the extreme high temperature and drought events. At present, the interactive effects of those extreme event stresses on maize growth at the grain filling stage are less well studied. In this study, a two-year field experiment was conducted to evaluate the compound effects of three stressors (high temperature, drought, and stress duration) at the filling phase on phenological period, grain filling rate, yield component, and yield of summer maize. The precipitation and temperature were controlled by using a rain-shelter systems and a warming system with infrared radiation lamps in field plots. The results indicated the significant influences of high temperature, drought stress, and the interaction on the growth and yield of summer maize. Under the individual factor of drought, compared to normal irrigation (NI), the significant decrease in grain-filling rate for mild drought (LD) and severe drought (SD) were 70.7% and 60.6%, respectively, while the decrease in grain yield for LD and SD were 80.1% and 93.6%, respectively. Under the individual factor of temperature, the consequences on grain-filling rate and grain yield were more severe at high temperature (temperature increase by 4.5 °C) than low temperature (temperature increase by 2.3 °C). The compound of high temperature and drought indicated that the grain yield increase by the compound effects of 3 °C for 5 days under normal irrigation (NIT₃D₅) and the compound effects of 3 °C for 7 days under mild drought (LDT₃D7) were 3.5% and 10.9%, respectively, compared to without temperature stress. The grain yields were reduced by the other compound effects. The preferential temperature (temperature increase by 2.3 °C) promoted maize growth under normal irrigation and mild drought, while high temperature (temperature increase by 4.5 °C) significantly inhibited maize growth under normal irrigation and heavy drought. The warming climate is favorable to maize production within certain limits, and will provide a scientific basis for agricultural disaster prevention and mitigation.

Global climate change significantly affects photosynthesis in spring wheat. However, the successive dynamic effects of multiple environmental interactions on photosynthesis in spring wheat have been inadequately investigated. This study conducted pot control experiments to determine photosynthesis characteristics, namely light and CO2 response curves, in spring wheat under progressive drought stress. Progressive drought stress caused all parameters of the light response curve to decrease logistically and all parameters of the CO2 response curve to change exponentially. There were noticeable thresholds for these parameter changes. The ability of spring wheat to utilize light was weakened by progressive drought stress. Under all drought levels, the reduction in photosynthetic capacity was greater under strong light than under weak light. The effects on CO2 utilization and the corresponding photosynthetic capacity depended on the drought level and CO2 concentration. The optimal light intensity (Iopt) for spring wheat showed a logistic decreasing trend under progressive drought stress. Unexpectedly, the optimal atmospheric CO2 concentration (CO2opt) remained at 800 µmol·mol− 1 under drought stress, which was less severe than extreme drought. Our results showed that progressive drought stress, combined with different environmental factors, had distinct impacts on the photosynthetic efficiency and carbon assimilation capacity of spring wheat, providing a basis for rational carbon and water resource utilization in spring wheat under climate change.

In order to deeply understand the effect mechanism of rapid drought stress on the physiological and biochemical properties of crop leaves and determine drought thresholds, the potted spring wheat under two water treatments, adequate water supply and continuous drought stress, was researched. In the early stage of drought, the parameters of leaves decreased in the order of stomatal conductance (g_s), intercellular CO₂ concentration (C_i), maximum electron transfer rate (J_max), mesophyll conductance (g_m), photosynthetic rate (P_n,) leaf water content (LWC), triose phosphate utilization rate (TPU), transpiration rate (T_r), and maximum carboxylation rate (V_cmax). Photosynthesis was dominated by stomatal limitation and also limited by carboxylation and mesophyll limitation. The carboxylation limitation was mainly caused by the reduction of electron transport capacity. In the late stage of drought, stomatal limitation first decreased, and then mesophyll limitation decreased. During extreme drought, carboxylation limitation also decreased. With the decrease of relative soil moisture (RSM), except for C_i, which first decreased and then increased, other physicochemical parameters of leaves all showed an S-shaped, decreasing trend. Mild and severe drought thresholds were determined to be 56.6% and 43.6% of the RSM, respectively, according to the curve’s inflection point, corresponding to 16.6% and about 52.2% of the average initial decrease amplitude among all parameters. This will provide a reference for monitoring as well as an early warning of rapid drought in spring wheat.