Low Temperature Enhances N‐Metabolism in <i>Paxillus involutus</i> Mycelia In Vitro: Evidence From an Untargeted Metabolomic Study

This metabolomic study investigates, using GC MS/MS analysis, the molecular response of Paxillus involutus mycelia to prolonged low temperature (4°C) exposure. Alongside reduced growth, decreased overall nutrient levels, and increased oxidative stress indicators, analyses revealed a significant increase in nitrogen (N) concentration and enhanced N metabolism, particularly via the GS-GOGAT pathway, which was associated with elevated concentrations of numerous amino acids. In contrast, carbon (C) metabolism was not intensified but largely reprogrammed, with varying changes in carbohydrate abundance but higher levels of several stress-related metabolites, such as trehalose and inositol family members, indicating activation of tolerance mechanisms, all with unchanged C (%). These changes suggest enhanced NH₄ ⁺ uptake and a redirection of glycolysis-derived C skeletons towards N-compound biosynthesis. The lack of massive upregulation of typical anti-stress compounds under low temperature exposure indicates either acclimatisation or mild stress. Mycelial restructuring, including increased dry mass (%) and accumulation of chitin precursors, implies cell wall remodelling and cold acclimatisation, supported by changes in membrane components. All these findings suggest that low temperatures may enhance N metabolism in ECM fungi even without additional carbon supply, potentially affecting symbiotic balance under climate change. Further studies are needed to validate these mechanisms and ecological implications.