Exogenous sulfur application can effectively alleviate iron deficiency yellowing in peanuts and increase pod yield

Iron deficiency yellowing is a serious and widespread problem that seriously affects plant growth and development, ultimately damaging plant yield. Sulfur is one of the essential elements for plant growth and development, and plays an important role in crop stress resistance. Iron (Fe) and sulfur (S) play a core role in the mineral nutrients required for plant metabolism, as both elements are essential for the activity of several proteins involved in basic cellular processes. This research used peanuts as materials to explore the effect of exogenous sulfur on alleviating iron deficiency and yellowing in peanuts under iron deficiency and iron enrichment levels. A two-year field experiment was conducted on windblown sandy soil to determine peanut yield, photosynthetic rate, photosynthetic pigment content, and the activity of key enzymes such as protective enzymes in leaves and roots. The results showed that the application of exogenous sulfur can increase pod yield by an average of 12.6 %-21.6 %. The application of exogenous sulfur significantly increased the migration of iron from roots to the ground, and increased the accumulation of active iron in young leaves by 42.6–73.2 %. Exogenous sulfur application increased the content of GSH in leaves, reduced the damage of Fe-deficient to leaf tissue structure, and effectively increased or maintained the accumulation of photosynthetic compounds in leaves. In addition, exogenous sulfur application at Fe-sufficient levels promoted dry matter accumulation while increasing N and S nutrient content, thereby increasing the N: S ratio. Therefore, exogenous sulfur application significantly increased the content of Chl a and Chl b in leaves, as well as the net photosynthetic rate. The application of exogenous sulfur increased the activity of SOD, POD, and CAT enzymes in roots and leaves, decreased the content of H₂O₂ and MDA in leaves, and reduced the rate of O_.^2- generation, thereby enhancing the plant's resistance to oxidative stress. This confirms that the application of exogenous sulfur and sufficient iron is of great significance in reducing iron deficiency yellowing in peanuts and improving yield.