Zeta diversity differentiates factors driving community assembly of rare and common ectomycorrhizal fungi

Abstract

A fundamental goal in community ecology is to understand what factors drive community assembly processes. The factors affecting ectomycorrhizal fungal communities are unknown in many regions, particularly in the southern hemisphere. We investigate community assembly using ITS2 metabarcoding of ectomycorrhizal fungi sampled from 3943 hyphal ingrowth bags buried in 81 Nothofagus forests across New Zealand's South Island. By applying zeta diversity analysis and multisite generalized dissimilarity modelling (MS‐GDM) we quantify the effects of 43 biotic and environmental variables on community turnover. Unlike traditional beta diversity analyses that are heavily influenced by rare species, the zeta diversity framework differentiates between factors driving turnover of rare and common species, providing a more complete picture of community dynamics. We found that community assembly was dominated by deterministic rather than stochastic processes and identified ecological factors affecting all taxa, as well as others that were specifically important to rare or common taxa. Soil variables were important drivers of turnover for all species, whereas ground cover variables, forest patch size, precipitation and host tree identity had greater effects on rarer species, and tree size and temperature effects were specific to more common species. Interestingly, the effect of temperature on common species is in line with recent evidence from other Kingdoms, pointing to possible generality, and highlighting the importance of considering common species. Applying these methods to fungi has allowed us to identify the distinct ecological processes that structure rare and common taxa during community assembly. This has important implications for understanding the functional effects of community responses to environmental change.

Trophic facilitation in forest restoration: Can Nothofagus trees use ectomycorrhizal fungi of the pioneer shrub Leptospermum?

“…Ectomycorrhizal fungal communities in pots were sampled using 4 × 4 cm hyphal ingrowth bags constructed from 50 μm nylon mesh and filled with 5 g of acid‐washed silica sand. Ingrowth bags largely select for active ectomycorrhizal mycelia growing in the soil (Bastias et al., 2006 ; van Galen, Orlovich, Lord, Bohorquez, et al., 2023 ; Wallander et al., 2001 ), and were chosen because sampling active hyphae provides an indication of the fungal species that have formed ectomycorrhizae with plants without the need to destructively sample seedlings. One disadvantage of this approach is that some taxa can show a preference for the substrate in the bag causing soil and bag communities to diverge, however, this effect is reduced with incubation times over 75 days (Hagenbo et al., 2018 ).…”

Correlated evolution in an ectomycorrhizal host–symbiont system

“…97.4% (3943 of 4050) of ingrowth bags were recovered from the field (see van Galen et al ., 2023). After collection, ingrowth bag contents were sequenced using Illumina MiSeq sequencing.…”

“…Three of the 810 plots were excluded from analyses, because no hyphal ingrowth bags could be recovered from two plots, and one plot contained no ectomycorrhizal sequences. Rarefaction curves showed the sequencing read depth of all 807 samples were sufficient to detect the vast majority of ASVs (van Galen et al ., 2023). Therefore, raw read counts were converted to presence/absence for each sample, and the data were summarised for each of the 81 sites by using the number of plots each ASV was recorded in as a measure of relative abundance (values ranged between 0 and 10).…”

Range reshuffling: Climate change, invasive species, and the case of Nothofagus forests in Aotearoa New Zealand

“…Occurrence data for the five Nothofagus species were restricted to New Zealand and collected from three sources: our own fieldwork (116 entries (van Galen et al, 2023)), the New Zealand Indigenous Carbon Monitoring System (Ministry for the Environment, 2012) (281 entries), and the online repository Atlas of Living Australia (ALA) (3452 entries). Atlas of Living Australia records were downloaded using the ‘galah’ R package version 1.5.0 (Westgate et al, 2022).…”