NO 3 − /NH 4 + ratios affect nutritional homeostasis and production of Tanzania guinea grass under Cu toxicity

Nitrogen (N) can alleviate metal toxicity. However, as of yet, there have been no studies showing the efficacy of NO 3 − /NH 4 + in mitigating Cu toxicity. The objective of this study was to evaluate the Cu toxicity on the nutritional and productive attributes of Panicum maximum cv. Tanzania as well as the role of NO 3 − and NH 4 + ratios in nutritional homeostasis. The experiment was conducted using 3 × 4 factorial treatments arranged in a randomized complete block design with three replicates. The treatments were three NO 3 − /NH 4 + ratios (100/0, 70/30, and 50/50) and four Cu rates (0.3, 250, 500, and 1000 μmol L −1 ) in nutrient solution. Copper concentrations in the diagnostic leaves (DL) were highest in plants grown under 70/30 NO 3 − /NH 4 + ratios and a Cu rate of 1000 μmol L −1 . In this combination, it was observed that DL had higher concentrations of NH 4 + , greater glutamine synthetase activity, lower chlorophyll concentration (SPAD value), and lower shoot dry mass, suggesting high disorders of nutritional homeostasis. Plants receiving N in the form of NO 3 − and 1000 Cu μmol L −1 showed that DL had lower concentrations of Cu, higher concentration of chlorophyll, higher NO 3 − concentration, higher nitrate reductase activity, and higher NO 3 − accumulation in the roots, suggesting a reduction in disorders of nutritional homeostasis. The disorders on mineral uptake, N assimilation, and biomass production caused by Cu toxicity are shown to be affected by NO 3 − /NH 4 + ratios, and N supply via NO 3 − allowed for better homeostasis of the forage grass.