Salicylic Acid and Pyraclostrobin Can Mitigate Salinity Stress and Improve Anti-Oxidative Enzyme Activities, Photosynthesis, and Soybean Production under Saline-Alkali Regions

Soybean is a widespread crop in semi-arid regions of China, where soil salinity often increases and has a significant harmful impact on production, which will be a huge challenge in the coming years. Salicylic acid (SA) and pyraclostrobin are strobilurin-based bactericides (PBF). Under rainfall-harvesting conditions in covered ridges, the exogenous application of SA and PBF can improve the growth performance of soybeans, thereby reducing the adverse effects of soil salinity. The objectives of this research are to evaluate the potential effects of SA and PBF on soybean growth in two different regions, Harbin and Daqing. A two-year study was performed with the following four treatments: HCK: Harbin location with control; SA1+PBF1: salicylic acid (5 mL L-1) with pyraclostrobin (3 mL L-1); SA2+PBF2: salicylic acid (10 mL L-1) with pyraclostrobin (6 mL L-1); DCK: Daqing location with control. The results showed that in the Harbin region, SA2+PBF2 treatment reduced the evapotranspiration (ET) rate, increased soil water storage (SWS) during branching and flowering stages, and achieved a maximum photosynthesis rate. Moreover, this improvement is due to the reduction of MDA and oxidative damage in soybean at various growth stages. At different growth stages, the treatment of Harbin soybean with SA2+PBF2 significantly increased the activity of CAT, POD, SOD, and SP, while the content of MDA, H2O2, and O-2(-) also decreased significantly. In the treatment of SA2+PBF2 in Harbin, the scavenging ability of free H2O2 and O-2(-) was higher, and the activity of antioxidant enzymes was better. This was due to a worse level of lipid-peroxidation which successfully protected the photosynthesis mechanism and considerably increased water use efficiency (WUE) (46.3%) and grain yield (57.5%). Therefore, using plastic mulch with SA2+PBF2 treatment can be an effective water-saving management strategy, improving anti-oxidant enzyme activities, photosynthesis, and soybean production.