Combined Effects of High Temperature and Drought on Yield and Photosynthetic Characteristics of Summer Maize

Climate change has led to global warming, with frequent occurrences of high temperatures and droughts, and high temperatures often accompany droughts during production. This study aimed to explore the physiological mechanism of the compound stress of high temperature and drought in different growth periods affecting the yield and photosynthetic characteristics of summer maize.

DH605 was selected as the experimental hybrid. High temperature treatment (T), drought treatment (D) and the compound stress (T-D) treatment were set in different growth periods. In 2019, it was carried out at the third leaf stage (V3), the sixth leaf stage (V6) and flowering stage (VT); In 2020, it was carried out at the third leaf stage (V3), the twelfth leaf stage (V12) and flowering stage (VT). This experiment took natural temperature and normal moisture treatment as control (CK). The effects of high temperature and drought compound treatments on yield, photosynthetic characteristics, dry matter accumulation and distribution of summer maize were studied, and the differences of photosynthetic characteristics and yield between single treatment and compound treatment were compared.

After the combined stress treatment of high temperature and drought in different growth stages, the LAI and SPAD of summer maize decreased significantly, which affected the net photosynthetic rate (P_n) and it decreased significantly. Among that, the compound stress during the VT period had the most significant effect on P_n. The P_n under T-D treatment in the VT period decreased by 39.0% on average compared with CK, while the net photosynthetic rate of summer maize after the combined treatment of high temperature and drought decreased more than that under single stress such as high temperature and drought. The combined treatment of high temperature and drought caused the photosynthetic performance of summer maize to decrease, and it led to the decrease of dry matter accumulation capacity and distribution ratio of summer maize to grains, which in turn led to a significant decrease in yield. In 2019, the output of T-D at V3, V6, and VT decreased by 27.4%, 18.3%, and 66.5%, respectively, compared with CK; in 2020, the output of T-D treatment at V3, V12, and VT decreased by 14.5%, 14.6% and 68.7%, respectively, compared with CK.

After the combined stress of high temperature and drought, the leaf area index and chlorophyll content was decreased, gas exchange was inhibited, leading to the decrease of photosynthetic performance, and thus hindered the accumulation and distribution of photosynthetic compounds, resulting in a significant yield reduction of summer maize. The combined stress of high temperature and drought during the flowering stage had the greatest impact on the yield and photosynthetic characteristics of summer maize, and the combined stresses had greater impacts than that of single stress.