Sulfur-Induced Changes in the Sugar Beet Leaf and Root Mycobiome

Sulfur (S) is a vital macronutrient involved in key physiological processes in plants, yet its role in shaping the plant-associated fungal microbiome remains underexplored. In modern agricultural soils, declining organic matter levels have contributed to widespread sulfur deficiency. Plants lacking in certain macro and micronutrients leads to hidden hunger. Therefore, healthier plants grown under optimized nutrient conditions not only contribute to sustainable agriculture but also to the production of nutrient-rich, higher-quality foods that support healthier diets and improved human well-being. This study investigates how varying sulfur availability influences the composition of fungal communities (mycobiome) associated with sugar beet (Beta vulgaris) leaves and roots. Sugar beet plants were grown under three sulfur conditions: zero sulfur (ZS), low sulfur (LS), and high sulfur (HS), in controlled pot conditions and no sulfur (NS) and optimal sulfur (OS) in hydroponics conditions. Physiological performance was evaluated using leaf reflectance spectroscopy to derive vegetation indices alongside shoot and root biomass measurements. Fungal communities associated with leaves and roots were characterized through rDNA region internal transcribed spacer 1 (ITS1) amplicon sequencing, with functional guilds classified using FUNGuild. The results revealed that adequate S supply enhanced chlorophyll content, photosynthetic efficiency, and biomass accumulation, while S deficiency triggered anthocyanin accumulation and stress-related spectral signals. Fungal diversity and composition were primarily driven by plant compartment (root vs. leaf) and growing conditions (soil systems vs. hydroponics), with specific guilds- such as endophytes, arbuscular mycorrhizal fungi, and epiphytes- responding differently to sulfur availability and growth system. Findings from this study could provide insights into optimizing sulfur fertilization to enhance beneficial plant-microbe interactions, with broader implications for sustainable agriculture. Additionally, the potential use of sulfur-enriched leaf material as a microbial biofertilizer is discussed, offering a promising avenue for circular nutrient use and crop residue valorization.