Characterization of Nutrient Disorders and Impacts on Chlorophyll and Anthocyanin Concentration of Brassica rapa var. Chinensis

Essential plant nutrients are needed at crop-specific concentrations to obtain optimal growth and yield. Foliar tissue analysis is the standard method for assessing nutrient levels in plants. Symptoms of nutrient deficiency or toxicity occur when the foliar tissue values become too low or high. Diagnostic nutrient deficiency criteria for Brassica rapa var. Chinensis (bok choy) is lacking in the current literature. In this study, green (‘Black Summer’) and purple (‘Red Pac’) bok choy plants were grown in silica sand culture, with control plants receiving a complete modified Hoagland’s all-nitrate solution, and nutrient-deficient plants induced by using a complete nutrient formula withholding a single nutrient. Tissue samples were collected at the first sign of visual disorder symptoms and analyzed for dry weight and nutrient concentrations of all plant essential elements. Six weeks into the experiment, the newest matured leaves were sampled for chlorophyll a, b, and total carotenoids concentrations for both cultivars, and total anthocyanin concentration in ‘Red Pac’. Compared to control plants, the dry weight of ‘Black Summer’ green bok choy was significantly lower for nitrogen (N), phosphorus (P), calcium (Ca), or boron (B) deficiency treatments, and nutrient concentrations were lower for all variables except iron (Fe) deficiency. Dry weight was less in ‘Red Pac’ plants grown without N, potassium (K), Ca, B, or molybdenum (Mo), and nutrient concentrations were lower for all except Mo-deficiency compared to controls. Total chlorophyll and total carotenoid concentrations were lower in leaves from N−, Fe-, and manganese- (Mn) deficient plants of both cultivars. Leaf anthocyanin concentration was lower only for K-, Ca-, and B-deficiencies in ‘Red Pac’. Our results indicate that visual symptoms of nutrient deficiency are well correlated with nutrient disorders. In contrast, changes in dry weight, chlorophyll, and anthocyanin did not show consistent changes across nutrient disorders.