Silicon attenuates the effects of water deficit in sugarcane by modifying physiological aspects and C:N:P stoichiometry and its use efficiency

Climate change has increased the occurrence of droughts and the use of deficient irrigation associated with silicon (Si) can be a strategy to mitigate water deficit in crops; however, the mechanisms involved have to be understood. The objective of this study was to evaluate whether the application of Si via fertigation associated with leaf spray mitigates the effects of water deficit by improving the physiological aspects and modifying C: N: P stoichiometry, inducing an increase in nutrient use efficiency in the ratoon of two sugarcane species (Saccharum officinarum- conventional sugarcane and S. spontaneum- energy cane). Two experiments were carried out in a greenhouse, using conventional sugar cane (variety-RB 966928) and energy cane (variety-VX2). In both experiments, the treatments were arranged in a 2 × 2 factorial scheme, without water deficit and with severe water deficit (30% of soil water retention capacity) without and with application of Si via fertigation associated with leaf spray, both in a concentration 2.5 mmol L−1, arranged in randomized blocks. At 80 days after ratoon regrowth, the following parameters were evaluated: Si content and accumulation, efficiency of using C, N and P, C: Si, C: N and C: P ratios, quantum efficiency of PS II, relative content of water, leaf water potential, leaf area, number of leaves and tillers and dry matter production. In the absence of Si, water deficit affected the physiological variables and the growth of the two sugarcane species. The supply of Si via fertigation associated with foliar spraying of soluble Si increased the absorption of this element in the ratoon of conventional sugarcane and energy cane, regardless of water condition. Si attenuated the effects caused by severe water deficit because of the increase in the relative water content and water potential, thus decreasing oxidative stress, impacting photosynthesis efficiency and also modifying the C: N: P stoichiometry, increasing use efficiency for these nutrients and the growth of the two study species.