A glimpse into magnesium application in wheat crop: an integrative effect of nutritional status and physiological responses

Abstract

Magnesium (Mg) is an important nutrient involved in many physiological and biochemical processes, but also neglected and termed “a forgotten element” since few researches are focusing on it. This study aimed to assess the effect of Mg application rates and sources evaluating the nutritional and physiological status of wheat plants. Treatments consisted in two Mg sources (magnesium oxide - MgO and magnesium sulfate - MgSO4) and six application rates (0, 7.5, 15, 30, 60, and 90 kg Mg ha-1 – applied in soil). The experiment was conducted in 2017, at the São Paulo State University Experimental Farm (FEIS/UNESP) to evaluate the physiological role of Mg in photosynthetic pigments concentration (chlorophyll a, b, total, pheophytin, and carotenoids) as well as Mg influence in nitrate, amino acids, sucrose, and total sugar, Mg and K concentrations in wheat grains and leaves. The Mg application improved photosynthetic apparatus and increased pigments concentration. This provided a more efficient translocation of sugars within the plant, leading to an increased sugars and K concentration in wheat leaves. The Mg application increased chlorophyll b and carotenoids concentration, suggesting an improvement in plant protection regarding reactive oxygen species (ROS). Magnesium uptake contributed to a greater conversion of nitrate into amino acids in leaves, however, no increase in Mg nor antagonist effect with K was observed in wheat grains. Magnesium sulfate (MgO) application was more efficient to supply Mg for wheat plants compared to MgO. Nonetheless, MgSO4 impaired total sugars in grains and leaves and sucrose concentration in grains, mostly under Mg rates between 7.5 and 30 kg Mg ha-1. Magnesium concentrationin wheat leaves increased, regardless of Mg application rate and source, mainly due to the high capacity of Mg uptake and translocation along Mg soil application. Our study provides a better understanding of several basic Mg mechanisms in wheat, indicating a positive impact of this “forgotten nutrient” in plant physiology, biochemistry, and nutrition.