Fungal communities can influence the productivity, composition, and survival of trees through cycling nutrients, providing resources, and altering pathogens. Thus, shifts in fungal communities could impact forests by altering interactions between trees and their environments. Fungal community composition may be shaped by stochastic and deterministic processes such as dispersal-limitation, environmental filtering, and partner specificity between trees and fungi. For tree species with large geographic ranges, we expect fungal assembly processes to change with environmental variation across the range of the tree partner. Due to specificity between trees and symbiotic fungi, we expect deterministic to outweigh stochastic processes in root compared with soil fungi. As some tree species have exceptional longevity, we also expected tree age to influence fungal community assembly.
We surveyed fungi in four stands of Pseudotsuga menziesii with tree ages up to 800 years along an 1,800 km north-south transect. We sampled roots and soil around 12 P. menziesii in each stand, aged the trees, and sequenced fungal rDNA to determine composition and richness from which we calculated the relative role of deterministic and stochastic assembly processes. We used null models to evaluate the relative importance of deterministic variable and homogenizing selection, and stochastic dispersal-limitation, drift, and homogenizing dispersal in fungal community assembly.
We detected 7,280 amplicon sequence variants with 5,270 associated with soil, 3,887 with roots and 1,877 found across both roots and soils. Deterministic processes dominated root and soil fungal communities at all sites except one where stochastic processes (i.e., dispersal-limitation and drift) controlled root-fungi. Despite the dominance of determinism in fungal community assembly, the proportion of processes differed by site. Assembly processes did not vary with tree age.
Taken together, we suggest that the local environment, water limitation, and partner-preference between trees and their associated fungi, influence fungal community composition across the range of P. menziesii. We conclude that while fungal communities occurring near P. menziesii are dominated by homogenizing selection, the role of neutral processes still has minor influence on community assembly and may be important in shaping spatially isolated communities and those with strong gradients of fungal diversity.
Author ORCID Identifier
Joseph D. Birch https://orcid.org/0000-0001-8644-7345
James A. Lutz https://orcid.org/0000-0002-2560-0710
Justine Karst https://orcid.org/0000-0003-0497-1552
Natural Science and Engineering Council of Canada
Utah Agricultural Experiment Station
Utah State University
Trees were cored and tree-rings measured to estimate the age of each tree. Soil and root samples were taken around P. menziesii and environmental DNA was extracted for amplification. The ITS2 region was amplified to identify fungal communities of each root and soil sample. Fungal sequences were quality filtered and rarefied to 90% of the minimum read abundance.
Birch, J. D., Lutz, J. A., Karst, J. 2022. Dancing with Douglas-fir: Determinism dominates fungal community assembly processes. Journal of Ecology.
54.6° N, 124.3° W ; 50.8° N, 120.3° W ; 41.6° N 112.0° W ; 37.6° N, 112.8° W
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This work is licensed under a Creative Commons Attribution 4.0 License.
Birch, J. D., Lutz, J., & Karst, J. (2022). Data for Dancing [Data set]. Utah State University. https://doi.org/10.26078/NG5A-9F05
Additional FilesPSME_Tree_Fungi_data.xlsx (2855 kB)
TreesSheet_PSME_Tree_Fungi_data.csv (3 kB)
SequenceSheet_PSME_Tree_Fungi_data.csv (3865 kB)
MetadataSheet_PSME_Tree_Fungi_data.csv (1 kB)
README_Birch.txt (6 kB)