Vulnerability of Xylem Embolism in Maize Cultivars with Different Drought Tolerance under Water and Salt Stress

Water deficit and soil salinization are the primary abiotic stress factors hindering maize growth. To assess the effect of water and salt stress on xylem embolism in maize and investigate the relationship between drought resistance and xylem vulnerability, a greenhouse experiment was designed using two maize cultivars, Zhengdan 958 (drought-resistant) and Denghai 605 (drought-sensitive). Four treatments were included: control (CK), water deficit (WD), salt stress (SS), and combined water and salt stress (WS). Various hydraulic characteristic indicators, such as stem xylem water potential, leaf xylem water potential, the specific hydraulic conductivity (Ks) and percentage loss of conductivity (PLC), were analyzed. Specific hydraulic conductivity curves and vulnerability curves were constructed, and the hydraulic safety margin (HSM) of the xylem was determined based on stomatal conductance (Gs). The results indicated that the hydraulic conductivity and embolism resistance of maize xylem were not correlated. Compared to Denghai 605, Zhengdan 958 had lower maximum specific hydraulic conductivity Ksmax and P50 values (xylem water potential at 50% PLC) in all treatments, indicating lower water transport capacity but stronger resistance to embolism. Under single-cultivar conditions, salt stress had a greater inhibitory effect on Ksmax and HSM in maize xylem compared to water deficit; thus, more severe embolism was found under salt stress. Under different treatment conditions, Zhengdan 958 had a larger HSM than Denghai 605, showing a wider water transport safety range and overall superior water transport security. To summarize, water and salt stress inhibited the water transport efficiency of the xylem in maize stems, and stronger drought-resistant cultivars showed greater resistance to embolism and larger hydraulic safety margins.