Nitrogen Stress Induced Modification of the Foliar Phytochemical Composition in Strawberries.

Secondary metabolites play a significant role in acclimatizing plants to various environmental stresses. Though many of these secondary metabolites have direct benefits to human health, the current agricultural practices, by providing optimal growing conditions, compromises the biosynthetic capacity of plants to produce phytochemicals. Our work focuses on the nutrient stress dependent inflection point of carbon partitioning between growth and production of phenylpropanoids in plants, and the occurrence of non-linear responses between nitrogen fertilization and phytochemical content. In the present study, we evaluated the effect of four levels of nitrogen fertilizer (12, 23, 44 and 81mg N) on the foliar content, composition and localization of metabolites in two cultivars (Camarosa and Albion) of Fragaria ananassa. Non-targeted metabolomics approach was used to capture the dynamics of primary and secondary metabolites, along with apparent activities of the rate-limiting enzymes of the key metabolic pathways.

In general, across both cultivars, the content of primary and secondary metabolites exhibited a contrasting trend with respect to N treatments, where the content of primary metabolites increased with N-sufficiency, whereas the content of secondary metabolites increased with N-deficiency. Non-targeted metabolomics putatively identified more than forty phenylpropanoids encompassing hydroxycinnmate derivatives, flavones, flavonols and flavan-3-ols. Both the total and extractable proanthocyanidins content decreased with increase in N fertilization, which then remained unchanged beyond 44 mg N, exhibiting a non-linear relationship of phytochemical content with N-treatments. In contrast, ellagitannins, encompassing castalgin and geraniin, initially decreased with increasing N, but increased at highest rate of N fertilization. Flavone content decrease from 12 to 44 mg N, but increased at 81mg N; however, flavonols did not show the increase at higher N-level, elucidating potential role of difference in the hydroxylation as a mode to mitigate N stress. In general, plants receiving lower N rates exhibited highest antioxidant capacity.