Climate-induced shifts in ectomycorrhizal explorations from long to short strategies along an elevation gradient

Ectomycorrhizal (EcM) fungi colonize over 60% of tree stems globally, yet how their hyphal morphology varies across environments remains unclear, and current methods for defining EcM mycelial morphology and foraging space lack reliability. Here, we analyzed the morphological traits of 53 262 EcM root tips of Abies fargesii var. faxoniana across elevational temperature gradients (0.2-5.1°C) and developed a species-morphotype-space (SMS) framework to quantify mycelial foraging strategies from root tips to the soil profile. Our results revealed considerable EcM morphotype complexity at the root tip level and distinct temperature- and soil nutrient-driven shifts in EcM morphology based on an elevational gradient. Short-hyphae dominated at lower elevation, whereas thicker long-rhizomorphs prevailed at higher elevation, reaching a foraging space of up to 1.02 × 10⁶ cm³ m^-3 soil. Short-hyphae mycorrhizas exhibited highly active hydrolytic enzymes, which enable them to increase resource availability and play a pivotal role in nutrient foraging. As temperatures rise, increased soil inorganic nitrogen availability in cold forests favors short-hyphae while suppressing long-rhizomorphs with high carbon retention capacity, potentially reducing soil carbon stability. Our analyses of EcM foraging space and multidimensional mycelial diversity provide new opportunities to predict how EcM hyphal processes respond to climate change.