Magnesium deficiency stress in rice can be alleviated by partial nitrate nutrition supply

Abstract

Abstract Magnesium (Mg) plays an imperative role in determining crop growth and development, but Mg-deficiency becomes more common, more severe and more widespread in farmland. The major source of nitrogen for rice is ammonium (NH4+). However, excessive application of NH4+ could inhibit Mg2+ uptake by rice. It has been accepted that partial nitrate (NO3-) nutrition may not only improve nitrogen (N) assimilation and rice growth, but also promote Mg2+ absorption. Nonetheless, the mechanisms underlying Mg and N interaction are not well documented. To explore the relationship between them in rice plant, a hydroponic experiment was conducted with different Mg (0.01, 1.00, and 5.00 mM) concentrations and various NO3-/NH4+ ratios (0/100, 25/75 and 50/50, %) under greenhouse conditions. Results showed that Mg-deficiency (0.01 mM) can cause yellow leaves, dwarf plants and fewer tillers during rice growth. Furthermore, Mg-deficiency treatment induced a major decrease in dry weight, root morphology and activity, photosynthetic properties, and Mg and N accumulation, while increase in antioxidant enzyme (MDA, SOD, POD and CAT) activities in rice, when compared with the high Mg (5.00 mM) or normal Mg (1.00 mM) treatment. The treatments with different NO3-/NH4+ ratios had no significant effect on these antioxidant enzyme activities in most cases under high or normal Mg conditions. However, under Mg-deficiency stress, the supply of partial NO3- lead to a significant drop in antioxidant enzyme activities. Moreover, partial NO3- supply significantly improved Pn, Tr, Gs and Ci under Mg-deficiency conditions. In particular, under Mg-deficiency stress, the supply of partial NO3- dramatically promoted the growth of the root system, boosted the occurrence of lateral roots, enhanced root vitality. Additionally, the supply of partial NO3- lead to significant increases of dry weight and N and Mg accumulation under the stress of Mg-deficiency. The results of this study suggested that the symptoms of Mg-deficiency stress in rice can be alleviated by partial NO3- supply.