Limited Impact of Arbuscular Mycorrhizal Fungi on Nitrogen and Water Inputs in Greenhouse Bell Pepper Cultivation

Bell pepper ( Capsicum annuum ) is a high-value vegetable crop with a projected global market size of $6-7 billion by 2033. Despite their broad adaptability, bell pepper acreage and yield in the United States have declined since 2000, both in open field and greenhouse conditions, largely due to increased production challenges such as international market competition, production and labor costs, and climate challenges. Some of these effects include more frequent abiotic stress events such as drought and heat, as well as heightened pest and disease pressure. Arbuscular mycorrhizal fungi (AMF) have been proposed as a biological strategy to improve crop resilience through enhanced water and nutrient acquisition; however, their effectiveness in intensive vegetable production systems remains unclear. Here, we report two studies. The first one evaluated the effects of commercial AMF inoculation on water use, stress tolerance, and plant performance in greenhouse-grown bell peppers. Pot-grown plants were subjected to well-watered and water-deficit irrigation regimes, with and without AMF inoculation. Water-deficit irrigation reduced fruit yield by approximately 50% compared to well-watered conditions, and AMF inoculation did not mitigate the effects of water deficit. A subsequent experiment assessed the influence of inoculation timing and method under two nitrogen fertilizer rates. No significant effects of inoculation treatment were also observed on plant growth or yield. These results indicate that irrigation and nutrient limitations exert a strong influence on greenhouse bell pepper productivity and suggest a limited benefit of AMF bioinoculants under controlled conditions.