Growth, Photosynthesis, and Gene Expression of Bermudagrass in Response to Salinity and Shade Stress

Soil salinization is an environmental problem globally. Bermudagrass (Cynodon dactylon) has long been used for soil restoration in saline-alkali land. Urbanization and the compound planting pattern combining trees, bushes, and grasses induced shading are becoming one of the most significant environmental constraints on the management of bermudagrass, which directly affects photosynthetic characteristics. Salinity and shade have become the most important environmental constraints on lawn development and implementation. Previous studies have shown that the plant physiological response under combined stress was different from that under single stress. The purpose of this research was to investigate the effects of salinity stress, shade stress, and the combined stress on bermudagrass. Shade nets were used to simulate shade stress to 85% shade. The NaCl concentration gradient for salinity stress was 1.0% for 7 days, 1.5% for 7 days, and 2.0% for 13 days, respectively. The combined stress combines the two approaches mentioned previously. The results showed that the salinity stress significantly inhibited the plant height, leaf relative water content, chlorophyll content, the chlorophyll a fluorescence induction (OJIP) curve and other photosynthetic parameters of bermudagrass while increasing electrolyte leakage when compared with control. Shade stress significantly enhanced the plant height, chlorophyll content, electrolyte leakage, the OJIP curve, and other photosynthetic parameters. Under the combined stress, the plant height and relative water content did not change significantly, but the photosynthetic parameters such as chlorophyll content and the OJIP curve increased. Furthermore, under the combined stress, the photosynthesis-related genes were regulated. Salinity stress inhibited the photosynthetic ability of bermudagrass more than shade stress, while the combined stress exhibited a considerably better photosynthetic ability. These findings provide information for the usage of bermudagrass in salinized shade conditions.