Early stage root-Associated fungi show a high temporal turnover, but Are independent of beech progeny

Abstract

The relationship between trees and root-associated fungal communities is complex. By specific root deposits and other signal cues, different tree species are able to attract divergent sets of fungal species. Plant intraspecific differences can lead to variable fungal patterns in the root's proximity. Therefore, within the Beech Transplant Experiment, we analyzed the impact of three different European beech ecotypes on the fungal communities in roots and the surrounding rhizosphere soil at two time points. Beech nuts were collected in three German sites in 2011. After one year, seedlings of the different progenies were out-planted on one site and eventually re-sampled in 2014 and 2017. We applied high-throughput sequencing of the fungal ITS2 to determine the correlation between tree progeny, a possible home-field advantage, plant development and root-associated fungal guilds under field conditions. Our result showed no effect of beech progeny on either fungal OTU richness or fungal community structure. However, over time the fungal OTU richness in roots increased and the fungal communities changed significantly, also in rhizosphere. In both plant compartments, the fungal communities displayed a high temporal turnover, indicating a permanent development and functional adaption of the root mycobiome of young beeches.

Keywords: Beech Transplant Experiment; Biodiversity Exploratories; Fagus sylvatica; Illumina sequencing; fungal ITS2; rhizosphere.

Figure 1

Schematic overview of the experimental design: (a) In October 2011 beech nuts were collected from four forest plots within the three sites of the Biodiversity Exploratories, i.e., Schwäbische Alb, Hainich-Dün, and Schorfheide-Chorin; (b) beech seedling grew in a greenhouse at Göttingen University; (c) in October 2012 beech seedling of different progenies were out-planted to nine forest plots per site; (d) in September 2014 and November 2017 beech trees on five Schorfheide-Chorin plots were sampled; (e) we collected roots and the attached rhizosphere soil and gained a total of 60 samples (three progenies × five plots × two sampling years × two compartments) for subsequent analyses of the beech root-associated fungal mycobiome.

Figure 2

Overview of relative fungal taxonomical (a,b) and guild-based (c,d) distribution amongst beech progenies and sampling years, Alb—Schwäbische Alb, Hai—Hainich-Dün or Sch—Schorfheide-Chorin.

Figure 3

Variability of total fungal, saprotrophic, symbiotrophic, and pathotrophic community assemblages in (a) rhizosphere and (b) beech roots from 2014 to 2017. Stacked bars represent overall beta-diversity (β_SOR) for the three beech progenies (Alb—Schwäbische Alb, Hai—Hainich-Dün or Sch—Schorfheide-Chorin), computed using the R package betapart [50], light grey sections of the bars represent the contribution of the fungal turnover (β_SIM) and dark grey sections account for the fungal nestedness (β_SNE).

Figure 4

Riverplots displaying the temporal development of general (a,b), saprotrophic (c,d), symbiotrophic (e,f) and pathotrophic (g,h) fungal OTUs from 2014 to 2017. The individual plots show in detail the proportions of OTU occurrences within the examined samples: beech progenies: Alb—Schwäbische Alb, Hai—Hainich-Dün or Sch—Schorfheide-Chorin, emerged OTUs did not appear in 2014, but in 2017. The contrary is the case for lost OTUs, which occurred in 2014, but no longer in 2017.