Measuring ectomycorrhizal fungal dispersal: macroecological patterns driven by microscopic propagules

Abstract

Dispersal plays a prominent role in most conceptual models of community assembly. However, direct measurement of dispersal across a whole community is difficult at ecologically relevant spatial scales. For cryptic organisms, such as fungi and bacteria, the scale and importance of dispersal limitation has become a major point of debate. We use an experimental island biogeographic approach to measure the effects of dispersal limitation on the ecological dynamics of an important group of plant symbionts, ectomycorrhizal fungi. We manipulated the isolation of uncolonized host seedlings across a natural landscape and used a range of molecular techniques to measure the dispersal rates of ectomycorrhizal propagules and host colonization. Some species were prolific dispersers, producing annual spore loads on the order of trillions of spores per km(2). However, fungal propagules reaching host seedlings decreased rapidly with increasing distance from potential spore sources, causing a concomitant reduction in ectomycorrhizal species richness, host colonization and host biomass. There were also strong differences in dispersal ability across species, which correlated well with the predictable composition of ectomycorrhizal communities associated with establishing pine forest. The use of molecular tools to measure whole community dispersal provides a direct confirmation for a key mechanism underlying island biogeography theory and has the potential to make microbial systems a model for understanding the role of dispersal in ecological theory.

Responses of Soil Fungi to Logging and Oil Palm Agriculture in Southeast Asian Tropical Forests

“…There is some evidence that changes in microbial communities may mediate the altered biogeochemical processes in historically disturbed soils [67,68], although the focus of land-use legacies has been on soil properties, while less research has elucidated the historical imprints on microbial communities themselves [68,69]. The long-term We found that forest to oil palm conversion resulted in far more dramatic shifts in soil fungal communities than historical by a recent study of EcM fungal dispersal, which documented dispersal limitation and significant decreases in EcM seedling colonization with increasing distance from forest edges [70]. The extent to which EcM fungi are undergoing local extinctions in the current fragmented landscape of Southeast Asia is unknown, but in the case that economic shifts result in the abandonment of oil palm cultivation, appropriate reservoirs for maintaining viable EcM fungal populations for dipterocarp tree regrowth will be essential.…”

Endemism and functional convergence across the North American soil mycobiome

“…Rapid community turnover at local scales and high degrees of endemism at the largest scales are most consistent with dispersal as an important driver of local and regional species pools. Studies of airborne fungal spores show that dispersal can be a limiting factor at the meter to kilometer scale (36,37). Similarly, evidence from population genetic (38) and phylogeographic (39) studies shows that large geographic features (e.g., oceans, mountains) are effective dispersal barriers to fungal populations.…”

Effects of dispersal and selection on stochastic assembly in microbial communities

“…For instance, greater efforts should be placed on the quantification and manipulation of microbial dispersal rates across microbial communities. Although several studies have tackled this challenge (Bruns, 1995;Bell, 2010;Lindström and Östman, 2011;Peay et al, 2012;Martiny, 2015), we need to pay careful attention to the methods (and units) for characterizing dispersal rate in order to generalize across studies and scales. A second key measurement in future studies should be microbial biomass and/or absolute abundance.…”