Within-Site Variations in Soil Physicochemical Properties Explained the Spatiality and Cohabitation of Arbuscular Mycorrhizal Fungi in the Roots of Cryptomeria Japonica

Abstract

Arbuscular mycorrhizal fungi (AMF) live in a community in the roots of host plants. Still, the patterns and factors that drive their spatiality and cohabitation remain uncovered, particularly that of trees in planted forests, which we aimed to clarify in Cryptomeria japonica, a major plantation tree in Japan. We analyzed 65 paired root and soil samples of Cryptomeria japonica trees collected from 11 microsite (MS) plots at two environmentally different forest sites in central Japan and measured soil pH, total phosphorus (TP), C, N, and the carbon-to-nitrogen ratio. Root AMF communities were recovered using Illumina's next-generation amplicon sequencing targeting the small subunit of ribosomal DNA. We detected more than 500 AMF OTUs at each site but only three belonging to Dominikia, Rhizophagus, and Sclerocystis were dominant in the roots of C. japonica, detected each at an average relative abundance higher than 20%. Two showed negatively correlated spatial distributions and different associations with soil pH. Similarly, the physicochemical properties at MSs significantly determined the AMF assemblages in the roots of C. japonica. Dominikia, Rhizophagus, and Sclerocystis coexist in the roots of C. japonica where soil physicochemical properties, particularly pH, determine their spatial dynamic, turnovers, and cohabitation patterns. These findings highlight the importance of simultaneous colonization of plants by multiple AMF.

Keywords: Community ecology; Elevation; Intraradical AMF community; Japanese cedar; Soil properties.

Fig. 1

Locations of microsite plots (MS) in the study areas, illustrating the sampling design. Five individuals of Cryptomeria japonica were collected from each MS at the University of Tokyo Chiba Forest (UTCBF, CB) and seven from each MS at the University of Tokyo Chichibu Forest (UTCF, CH). At UTCBF, MSs 1–3 and 4–6 were planted with the cultivars “Sanbu-sugi” (SS) and “Kuro-sugi” (KS) of Cryptomeria japonica, respectively. Data were not available regarding the cultivars planted at UTCF

Fig. 2

Non-metric multidimensional scaling (NMDS) and redundancy analysis (RDA) plots of arbuscular mycorrhizal fungi (AMF) communities in the roots of Cryptomeria japonica investigated spatially at two sites. NMDS followed by permutational analysis of variance (PERMANOVA) tests of the AMF communities in the roots of C. japonica among microsite plots (MS) at the University of Tokyo Chiba Forest (a UTCBF) and Chichibu Forest (b UTCF). PERMANOVA tests for RDA showing linear relationships between components at UTCBF (c) and UTCF (d). TC, total carbon; TN, total nitrogen, C/N, carbon-to-nitrogen ratio; TP, total phosphorus. In panels c and d, AMF OTUs, environmental variables, and samples are labeled in red (starting with OQ), blue, and green (starting with CB for UTCBF and CH for UTCF), respectively. KS (“Kuro-sugi”) and SS (“Sanbu-sugi”) refer to the cultivar of Cryptomeria japonica planted in a given MS

Fig. 3

Genus composition of arbuscular mycorrhizal fungi (AMF) communities in the roots of Cryptomeria japonica investigated spatially at two sites. These compositions are based on the NCBI GenBank and MaarjAM databases. CB and CH refer to sites UTCBF and UTCF, respectively

Fig. 4

Phylogenetic tree of major operational taxonomic units (OTUs) of arbuscular mycorrhizal fungi (AMF) in the roots of Cryptomeria japonica investigated spatially at two sites. A maximum likelihood tree was constructed using representative sequences of major OTUs (33 nucleotide sequences) and 14 reference nucleotide sequences downloaded from the NCBI GenBank and MaarjAM databases. The best model and parameters were selected using the automatic model finder in IQ-TREE 2. The SH-aLRT test and ultrafast bootstrap (UFBoot) process were performed over 1000 randomizations. SH-aLRT/UFBoot are shown at nodes where SH-aLRT ≥ 80% and UFBoot ≥ 95%. Accession numbers of major OTUs (shown in green for UTCBF and blue for UTCF) and the scientific names of reference sequences followed by their accession numbers were used as labels. Aligned sequences covered 562 sites of the small subunit ribosomal DNA between primers NS31 and AM1