Dancing with Douglas‐fir: Determinism dominates fungal community assembly processes

Abstract

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 geographical 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 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. Synthesis. 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 a minor influence on community assembly and may be important in spatially isolated communities and those with strong gradients of fungal diversity.

Fungal diversities and community assembly processes show different biogeographical patterns in forest and grassland soil ecosystems

“…Our observation in the context of different habitats is in line with the results of recent large-scale studies in natural soil from different habitats across Scotland ( Powell et al, 2015 ), suburban agricultural districts of Shanghai, China ( Li et al, 2021 ), and a wine-growing region of Italy ( Larsen et al, 2022 ). In contrast to our finding, however, Birch et al (2022) , who reported that deterministic processes, particularly homogenizing selection, dominated fungal communities along an 1,800 km transect of North America across Pseudotsuga forests. Our results indicate a greater tendency toward stochastic processes, which is inconsistent with the seminal work of Zheng et al (2021) , who highlighted a substantial divergence among whole fungal communities and the AM and EM fungal community subsets within and among 12 forest ecosystems along a large latitudinal gradient.…”

Compartment and Plant Identity Shape Tree Mycobiome in a Subtropical Forest

“…Similarly, previous studies demonstrated that soil fungal community assemblies were strongly shaped by deterministic (niche-based) factors (e.g., [ 40 , 41 ]). For root-associated fungal communities, deterministic processes dominated at most of the sites ( 42 ), while neutral processes still had a minor influence on community assembly and might be important in spatially isolated communities as well as those with strong gradients of fungal diversity ( 42 , 43 ). According to the lower migration rate of the leaf compartment than that of the root and soil compartments, our results suggested that fungal communities in the phyllosphere were less affected by deterministic process than were those in the other two compartments.…”

Attribution of dispersal limitation can better explain the assembly patterns of plant microbiota

“…These clues indicate that variation in the composition and structure of the root endophytic microbiota is non-random. Interestingly, recent studies applying the ecological null modeling framework have confirmed that the assembly of the root endophytic microbiota is primarily affected by stochastic processes ( Table 1 ; Figure 2 ) ( Birch et al., 2022 ; Tian et al., 2022 ; Zhong et al., 2022 ). Although this finding explains why stochastic assembly dominates the endophytic root microbiota: via priority effects—microorganisms that arrive first at a location have positive or negative effects on those that arrive later—and competitive exclusion, it contradicts the previously established consensus that roots are a highly selective environment that recruits specific microbial taxa via different exudation patterns.…”

“…Detailed information on each treatment group can be found in the original literature cited. Brassica napus ( Bell et al., 2022 ), grass species ( Zhong et al., 2022 ), Panicum miliaceum ( Tian et al., 2022 ); Pseudotsuga menziesii (PM) ( Birch et al., 2022 ), Populus ( Dove et al., 2021 ), and Camellia sinensis (CS; unpublished data).…”