Evaluating three foliar-applied biostimulants for Asian leafy green production under high tunnel conditions

Asian leafy greens are a group of cool-season vegetables valued for their versatility, nutritional quality, and rapid growth, and have been increasingly cultivated in various growing systems and climates. The applications of various biostimulants have been reported to increase crop productivity and alleviate stress in the production of several specialty crops. The current study evaluated plant growth, gas exchange, and mineral nutrient compositions of five Brassica rapa cultivars grown in a high tunnel as affected by three foliar applied biostimulants. Results revealed that the five cultivars varied in plant height, crown diameter, leaf SPAD and coloration, leaf and substrate temperatures, marketable yield, physiological parameters, and leaf mineral concentrations. 'Win Win Choi' produced the highest fresh shoot weight of 669.1 g·plant−1, and the highest marketable yield of 1.84 kg·m−2. The biostimulant treatments did not affect plant size, coloration, marketable yield, fresh or dry shoot weights, but altered physiological parameters, including leaf temperature, quantum efficiency, electron transport rate, and mineral nutrient uptake, including concentrations of phosphorus (P), potassium (K), calcium (Ca), iron (Fe), and copper (Cu). Under high tunnel conditions, the five Brassica rapa cultivars exhibited distinct growth, physiological responses, and nutrient uptake, which were largely attributed to genetic variation, whereas the biostimulant application could potentially yield more benefits when plants are subjected to suboptimal growing conditions with abiotic stresses.