Biochar Application Maintains Photosynthesis of Cabbage by Regulating Stomatal Parameters in Salt-Stressed Soil

Abstract

Salinity is one of the main abiotic stresses, and the stomatal conductance (gs) is an important physiological index in plants that is used to measure their responses to salt stress, as stomatal closure leads to lower yields. However, the factors that affect the gs after biochar application in saline soil remain unclear. To explore the stomatal adaptation mechanisms of facility vegetables under salt stress after the addition of biochar, Chinese cabbage was selected for the pot experiment in this study. The soil and plant Na+ and K+ concentrations, water status, and plant stomatal parameters were measured following treatments with different salt concentrations (25, 50, and 100 mM) and biochar application rates (0, 2, and 4%). The results showed that salt stress induced the physiological closure of the stomata in Chinese cabbage. Compared with the salt-stress treatment without biochar, the biochar application significantly increased the plant gs (20.29–128.79%). Moreover, in the biochar treatment, the open state of the stomata was maintained by sustaining the plant osmotic adjustment, reducing the abscisic acid (ABA) content, and improving the water status. The Na+/K+ ratio had the most pronounced effect on the stomata (0.702). The actual photochemical efficiency of the photosystem II (ΦPSII) and electron transport rate (ETR) of the Chinese cabbage increased by 0.75–3.41% and 0.65–2.88%, respectively, after the biochar application, which supported the photosynthetic capacity and yield formation. According to the current findings, biochar application can mitigate salt stress and regulate stomatal opening, thereby improving the photosynthesis and the overall yield of Chinese cabbage. Therefore, the application of biochar is a promising method to maintain the productivity of Chinese cabbage under salt stress.