Arbuscular Mycorrhizal Fungi and Azospirillum brasilense Enhance Growth and Resource Use Efficiency of Tomato Under Resource‐Limited Peat‐Reduced Cultivation

Abstract

The transition towards peat‐reduced and resource‐efficient horticultural systems presents challenges for maintaining crop productivity because of altered nutrient dynamics and reduced microbial diversity within soilless substrates. Beneficial microbial inoculants may provide a sustainable approach to improve plant performance under reduced‐input cultivation; however, their effectiveness in peat‐reduced hydroponic environments remains poorly understood. This study evaluated the effects of arbuscular mycorrhizal fungi (AMF; Rhizophagus irregularis) and nitrogen‐fixing bacteria (NFB; Azospirillum brasilense), applied individually and in combination, on growth, productivity, resource‐use efficiency, and substrate nutrient dynamics of tomato grown under restricted fertigation in a peat‐reduced hydroponic system. NFB primarily enhanced vegetative growth, increasing leaf number by 11.7% and shoot fresh weight by 40%. AMF increased total fruit weight by 46% and exerted a significant positive main effect on WUE and NUE. Co‐inoculation produced the highest numerical responses, increasing shoot and root fresh biomass by 48% and 74%, fruit number by 80%, fruit weight by 77% and co‐inoculation increased substrate nitrate (NO3−) and potassium (K+) concentrations by 45% and 21%, respectively, compared with the control. Although co‐inoculation frequently produced the greatest numerical responses, interaction effects were generally limited, indicating complementary rather than strongly synergistic functions between the two microbial groups. Fruit quality characteristics, including total soluble solids and marketable fruit percentage, were not significantly affected by microbial treatments. Overall, these findings demonstrate complementary roles of AMF and A. brasilens under peat‐reduced cultivation, highlighting the potential of microbial inoculants to support more sustainable, low‐input greenhouse production systems.