New Findings on the Concentration-Dependent Effects of Salicylic Acid and the Mitigation of Blue Light Stress on Canola Growth and Methane Emissions

Plant-derived methane (CH4) has already been reported, but the factors that regulate its production are not fully documented. Few studies have considered the effects of blue light on plant-derived CH4, but the role of salicylic acid in the process has not been studied. We examined the effects of two blue light levels (0 and 4 mW cm−2) and two salicylic acid concentrations (0 and 100 μL of 1 mM solution every other day) on canola (Brassica napus) growth and CH4 emissions by growing plants under the experimental conditions for 21 days. Blue light raised CH4 emission by 184% and increased stem height, leaf area ratio, shoot–root mass ratio, nitrogen balance index, leaf water potential, soil water potential, and leaf water content, but decreased stem diameter, plant biomass, specific leaf mass, net CO2 assimilation, photochemical quenching, photosynthetic pigments, flavonoids, and anthocyanins. Salicylic acid did not have a significant effect on plant traits. Methane had both positive and negative relationships with plant traits; for example, CH4 was negatively correlated with plant dry mass (r = −0.776, p = 0.003), protective compounds (r = −0.914, p = 0.000) and stomatal density (r = −0.677, p = 0.016), but positively correlated with nitrogen balance index (r = 0.621, p = 0.031). Our findings suggest that blue light negatively affects canola growth but increases CH4 emissions, whereas the application of salicylic acid, as described in this study, was insufficient for mitigating stress in plants.