Plant Molybdenum Uptake as Mediated by Synergism with Phosphorus but Antagonism with Sulfur in a Nitrogen-Fertilized and Mown Meadow

Whether molybdenum (Mo) addition promotes Mo uptake by plants in nitrogen-fertilized ecosystems may depend on nutrient interactions. But this has rarely been paid attention to in continuously mown and nutrient-losing grassland ecosystems. We investigated Mo uptake by three dominant species and plant community and how it varied with plant phosphorus and sulfur concentrations after 6-year and 7-year combined nitrogen and Mo addition and mowing management in a cold meadow. Molybdenum addition increased Mo concentrations in the three plant species and plant community across all treatments due to increased soil available Mo. Without Mo addition, nitrogen addition significantly reduced Mo concentrations of Leymus chinensis and plant community irrespectively of mowing and of Stipa baicalensis with mowing. With Mo addition, the negative nitrogen addition effect on plant Mo absorption was boosted for all plant species and plant community. This could be due to the fact that increases in plant sulfur absorption possibly induced antagonistic effects on plant Mo uptake. Additionally, reductions in plant phosphorus concentration weakened the synergistic uptake of Mo by plants with nitrogen addition, except for Carex duriuscula . Mowing only reduced Mo concentration of S. baicalensis without nitrogen addition under Mo addition. Our results indicated that plant Mo deficiency could occur in nitrogen-fertilized ecosystems via nutrient interplay, facilitating it a necessity to supplement Mo. In turn, Mo addition could somewhat amplify the interplay of Mo with S and P uptake by plants, calling for future studies to consider dosage threshold of nutrient interactions when optimizing fertilization strategies.