Temperature-dependent Effects of Arbuscular Mycorrhizal Fungi on Growth, Antioxidant Activity, and Heat Shock Protein Expression in Long Bean (Vigna unguiculata ssp. sesquipedalis).

Arbuscular mycorrhizal fungi (AMF) are known enhancers of plant abiotic stress tolerance, yet their responses to varying temperatures and subsequent effects on host physiology remain less understood. Here, long bean (Vigna unguiculata ssp. sesquipedalis) plants were cultivated under three temperature conditions 25 °C, 35 °C, and outdoors (fluctuating 24-43.5 °C) to assess AMF community diversity, plant root colonisation, phenotypic traits, physiological traits, and heat shock protein (hsp) gene expression. AMF-targeted amplicon sequencing and morphological analyses showed AMF diversity to be higher with elevated and fluctuating temperatures; outdoor conditions supported greater taxonomic diversity, including Acaulospora, Claroideoglomus, Diversispora, and Archaeospora, while Glomus remained dominant across all treatments. Among the growing conditions, root colonisation was highest at 25 °C. AMF inoculation significantly enhanced leaf number and chlorophyll content, and promoted antioxidant enzyme activities, with the strongest responses observed at 35 °C. In contrast, qRT-PCR analysis of 13 hsp revealed that AMF colonisation had little effect on expression with only Vuhsp26.5 showing significantly increased expression at 35 °C. Temperature influenced transcriptional patterns of three of the 13 hsp, with Vuhsp, Vuhsp22.7-1 and Vuhsp26.5 markedly upregulated at 35 °C compared to 25 °C and outdoor conditions. Collectively, these results demonstrate that AMF inoculation contributes to improved performance in V. unguiculata through enhanced antioxidant defence, while temperature exerts a dominant role in shaping both AMF diversity and hsp gene regulation. This study highlights the context-dependent nature of AMF plant interactions and provides insights into their potential role in improving crop resilience under warming climates.