A global synthesis reveals that environmental factors drive the proportion of ectomycorrhizal exploration types

Exploration types serve as a link between the morphological characteristics of hyphae in ectomycorrhizal fungi and the diverse nutrient-acquisition strategies employed by ectomycorrhizal trees. However, the influence of biological, climatic, edaphic and geomorphic factors on the prevalence of the contact and short-distance exploration types (CS) versus the medium-distance and long-distance exploration types (ML) remains inadequately understood within global forest ecosystems. Here, we conducted a global synthesis of 458 observations across 310 forest stands derived from 58 studies. We found that the proportion of CS exhibited unimodal patterns, while the proportion of ML displayed reverse unimodal patterns, in relation to latitude and nitrogen deposition. The proportion of CS decreased linearly, while that of ML increased non-linearly, leading to the decreased CS/ML ratio with advancing stand age. The CS/ML ratio significantly decreased with rising soil magnesium concentration. The relationships of the proportions of CS and ML with biological, climatic, edaphic and geomorphic factors varied among genus identities such as Picea and Pinus. They showed contrasting relationships of the proportions of CS and ML with soil pH and mean annual precipitation. The observed variations in exploration types underscore a significant shift in the resource exploration strategies of different hosts in forest ecosystems at various successional stages in response to alterations in nutrient/water availability. These changes have implications for the carbon sequestration capacity and potential of global forest ecosystems in the context of ongoing global climate change.