Pehim Limbu, S.; Sturmer, S. L.; Zahn, G.; Aguilar-Trigueros, C.; Rogers, N.; Chaudhary, V. B.

Climate-driven variation in microbial traits is crucial for predicting ecological responses to environmental change, yet global patterns remain understudied. Using global datasets of arbuscular mycorrhizal (AM) fungal observations linked to spore morphology, we show that climate gradients shape spore trait variation and functional diversity. Temperature and precipitation emerged as key drivers, influencing species range size and trait-environment relationships through trade-offs. Larger spore volumes were more prevalent in warm, wet, stable climates but were associated with smaller species range size s, suggesting a trade-off between persistence and dispersal potential. Spores with ornamentation were also more prevalent in warm, wet climates and linked to restricted range sizes, possibly reflecting specialization to specific environmental conditions. Cell wall investment decreased in warmer, wetter climates, and was the strongest predictor of species range size, with intermediate investment associated with broader geographic distributions. Spore shape and color also exhibited climate-driven patterns, with spherical spores and greater pigmentation more common in warm, wet climates. Phylogenetic analyses revealed high trait conservatism for spore ornamentation, moderate for volume, low for color, and none for shape and cell wall investment. Additionally, functional diversity analyses revealed that warm, wet environments promote within-community trait richness but lower trait divergence, while broader climatic variability drives higher beta diversity. These findings highlight the role of climate in shaping microbial trait biogeography and suggest that evolutionary history constrains some traits while others are adaptable, suggesting that ongoing climate change may restructure AM fungal distributions, impacting plant-fungal interactions, nutrient cycling, and ecosystem stability.