Root Colonization by Arbuscular Mycorrhizal Fungi Does Not Improve Greenhouse Bell Pepper Performance under Water Deficit and Different Nitrogen Regimes

Abstract

Bell pepper ( Capsicum annuum L.) is a high-value vegetable crop, and its productivity in greenhouse and controlled-environment systems depends strongly on irrigation and nutrient management. Arbuscular mycorrhizal fungi (AMF) have been proposed as biological tools to improve plant water and nutrient acquisition, but their functional value in intensively managed vegetable systems remains uncertain. This study evaluated whether commercial AMF inoculation improves physiological performance, growth, yield, nutrient status, and root colonization in greenhouse-grown bell pepper. Two complementary experiments were conducted using a commercial AMF product containing Rhizophagus irregularis, Funneliformis mosseae , Rhizophagus aggregatum, and Claroideoglomus etunicatum. In the first experiment, pot-grown plants were subjected to well-watered or water-deficient irrigation regimes, with or without AMF inoculation at seeding. Water deficiency reduced stomatal conductance, increased leaf temperature, decreased plant height and biomass, and substantially reduced fruit yield relative to well-watered conditions. Although AMF-inoculated plants showed measurable root colonization, inoculation did not improve water consumption, delay wilting, increase stomatal conductance, enhance photochemical efficiency, or mitigate yield losses under water deficit. In the second experiment, the timing and method of AMF application were evaluated at two nitrogen fertilizer rates. Inoculation at seeding and direct placement near the root zone increased AMF colonization compared with later or irrigation-based application methods; however, neither inoculation treatment nor nitrogen rate significantly affected plant height, shoot or root biomass, fruit yield, foliar nutrient status, or time to flowering. Overall, these results indicate that AMF root colonization does not necessarily confer physiological or agronomic benefits in intensively managed greenhouse bell pepper production. The effectiveness of commercial AMF bioinoculants appears to be highly context dependent and may be limited when irrigation and fertigation already provide favorable resource availability.