The Impact of Silicon on Photosynthetic and Biochemical Responses of Sugarcane under Different Soil Moisture Levels

Increasing drought stress is one of the most limiting factors for agricultural crop productivity across the world. Silicon (Si) has been known to augment plant protection against drought stress. In this experiment, the responses of sugarcane with silicon application to drought stress for photosynthetic and biochemical activities were investigated. Three water regimes [75 ± 5, 50 ± 5 and 25 ± 5% of soil water content capacity (SWCC) from 70 to 115 days after transplanting] and six silicon levels such as 0, 20, 40, 60, 80 and 100 g CaO.SiO2 pot−1 equivalent to 0, 194, 387, 581, 774 and 968 mg Si kg−1 soil, respectively, were applied. This experiment was arranged in a completely randomized block design. It was found that water stressed plants with silicon application showed increasing trends in photosynthetic CO2 assimilation (~2–106%), stomatal conductance (~8–113%), transpiration (~13–274%) and chlorophyll fluorescence yield (~0.3–10%) of 75 ± 5, 50 ± 5 and 25 ± 5% of SWCC as compared to the controls without Si application. The silicon application improved the plant growth under water stress, accompanied with the up-regulation in leaf relative water content (~2–8%), photosynthetic pigments (~2–35%), activities of catalase (ca. 12–91%), peroxidase (ca. 7–30%) and superoxide dismutase (ca. 3–96%) enzymes. These results indicate that Si fertilizer plays an important role in mitigating the negative effects of drought stress on sugarcane plant growth by improving water status, photosynthetic parameters and activating the antioxidant machinery. Findings demonstrated the silicon application an efficient strategy to improve sugarcane tolerance to drought stress.