Inoculation and co-inoculation of lettuce and arugula hydroponically influence nitrogen metabolism, plant growth, nutrient acquisition and photosynthesis

The objective of this study was to investigate the effects of single and combined inoculations of <i>A. brasilense, B. subtilis</i> and <i>P. fluorescens</i> on lettuce and arugula grown in a hydroponic system. The study was carried out in a greenhouse and was designed in randomized blocks with five replications. The treatments consisted of inoculation with <i>A. brasilense, B. subtilis</i> and <i>P. fluorescens</i> and co-inoculation with <i>A. brasilense + B. subtilis, A. brasilense + P. fluorescens, B. subtilis + P. fluorescens</i> and <i>A. brasilense + B. subtilis + P. fluorescens</i> via nutrient solution. An increase in the length and fresh mass of the shoot and leaf chlorophyll concentrations of arugula and lettuce was observed under co-inoculations of <i>A. brasilense + P. fluorescens</i> and <i>B. subtilis + P. fluorescens</i>. Greater length, fresh mass and volume of the lettuce root system were observed under the co-inoculations of <i>A. brasilense + B. subtilis, A. brasilense + P. fluorescens</i> and <i>B. subtilis + P. fluorescens</i> in arugula under the inoculations of <i>A. brasilense</i> and <i>A. brasilense + P. fluorescens.</i> Greater nitrate reductase activity was detected in leaves, and lower nitrate accumulation was detected in lettuce and arugula under inoculations with <i>A. brasilense, P. fluorescens</i> and <i>B. subtilis + P. fluorescens</i>. The greatest accumulation of N, P, K, Ca and Mg in the lettuce shoot was obtained under inoculation with <i>P. fluorescens</i>, <i>A. brasilense + P. fluorescens</i> and <i>B. subtilis + P. fluorescens</i>. Co-inoculation with <i>A. brasilense + P. fluorescens</i> and <i>B. subtilis + P. fluorescens</i> was the most efficient combination for increasing the growth, nutrient acquisition and functioning of nitrogen metabolism in arugula lettuce plants.