Chemical Forms of Nitrogen Fertilizers Differentially Influence the Content and Composition of Aroma Volatiles and Phytonutrients in Strawberry Fruits

as the major N form taken up by plants in this treatment. Although ammoniacal-N fertilization resulted in lower plant biomass, the fruit yield and tissue nutrient content were similar to those of nitrate-N treatments. The plant biomass of organic-N treatment was similar to that of nitrate-N fertilization, but the fruit yield was 30% lower. Compared to nitrate-N treatment, aroma-related volatile compounds increased under organic- and ammoniacal-N fertilization, including up to a 5-fold increase in esters, a 6-fold increase in alcohols, a 3-fold increase in volatile fatty acids, and a 60% increase in organic acids. The content of primary metabolites, especially sugar, sugar alcohol, and amino acids, exhibited an opposite trend and increased in nitrate-N than under ammoniacal- and organic-N fertilization. Compared to nitrate-N, the secondary metabolites generally were higher under ammoniacal- and organic-N fertilization, with an 80% increase in the activity of phenylalanine ammonia lyase, resulting in up to 38% increase in flavones, 28% increase in flavanols, and 33% increase in anthocyanins, except for dihydroflavonols and proanthocyanidins, which decreased by 6 and 13%, respectively. The hydrolyzable tannins, including galloyl glucosides, ellagitannins, and ellagic acids, were 25% abundant under organic-N fertilization. Our results indicate that while nitrate-N generally increased the primary metabolites, organic-N and ammoniacal-N fertilization enhanced the aroma-related volatiles and secondary metabolites in strawberry fruits. Thus, precise management of the chemical form of N fertilization can be a valuable tool to improve the phytonutrient content of strawberries.