Soil physical and chemical properties
Soil pH value in the sampling area was between 3.57 and 5.01, which had a significant difference between bamboo forest area and the non-bamboo forest area (Table 1). As the samples from the non-bamboo forest area (J2) and marginal area of bamboo forest (J3) gradually approached to the core area of bamboo forest (J1), soil water content, total organic carbon (TOC) and NO3−-N gradually decreased, and the difference between J2 and J1 was significant.
Table 1
Determination of soil physical and chemical properties in the study area
sample | pH | water content(%) | SOM (g/kg) | TN (g/kg) | TP (g/kg) | NO3−-N(mg/kg) | NH4+-N(mg/kg) | Pavi (mg/kg) |
J1 | 4.06 ± 0.17b | 40.91 ± 1.98b | 163.95 ± 8.15b | 3.56 ± 0.14b | 1.10 ± 0.05c | 0.62 ± 0.03b | 3.03 ± 0.13a | 4.17 ± 0.20c |
J2 | 4.76 ± 0.25a | 47.78 ± 2.35a | 183.45 ± 9.07a | 6.82 ± 0.29a | 9.90 ± 0.50b | 0.84 ± 0.04a | 2.12 ± 0.09b | 5.16 ± 0.23b |
J3 | 3.73 ± 0.16b | 42.22 ± 2.01b | 165.59 ± 8.26b | 1.94 ± 0.07c | 15.93 ± 0.71a | 0.80 ± 0.04a | 1.28 ± 0.06c | 6.36 ± 0.33a |
*Note: different lowercase letters in the same column indicated significant differences at the level of 0.05. |
Fungal sequence validity and Venne diagram
In the study area, 252036 effective sequences were obtained. The average length of the sequences used for subsequent analysis was 225 ~ 233nt (Fig. 1(a)). The quality of sequencing data was mainly distributed above Q20 (Fig. 1(b)), which could ensure the normal progress of subsequent analysis.
Valid sequences were clustered according to 97% similarity (Fig. 2). Through clustering, a total of 718 fungal OTUs were obtained from the study area. The number of fungal OTUs in the core area of bamboo forest (J1), non-bamboo forest area (J2) and marginal area of bamboo forest (J3) were 463, 377 and 431, and the number of unique fungal OTUs was 144, 94 and 112, respectively. The number of co-ownership OTUs was 185 among the three plots. On the whole, the ratios of OTUs number and the unique OTUs number to total OTUs number were shown as lowest in J2 ( 29.66%, 7.40%, respectively), increased in J3 (33.91%, 8.81%), and highest in J1 (36.43%, 11.33%). The results indicated that both fungal number and endemic species increased when the sample gradually transitioned from non-bamboo forest area to the core area of bamboo forest.
Soil microbial community diversity
The Alpha diversity indices of soil fungal communities under the 97% consistency threshold were shown in Table 2. The Goods coverage indices of the three samples were closed to or equaled to 1, which indicated that the sequencing depth was reasonable and the species coverage was high. The number of observed fungal species increased from the non-bamboo forest area (J2) to the core area of bamboo forest (J1), and the lineage diversity index (PD whole tree) also showed similar results. It suggested that the fungal community in J1 was more complex and had greater species diversity, and its fungal community diversity and uniformity were higher than those of the marginal area of bamboo forest (J3), however its species richness and the number of rare species were lower than those of J3.
Table 2
Analysis of sample species diversity
sample | Goods coverage | Observed species | PD Whole Tree | Shannon | Simpson | Chao1 | ACE |
J1 | 0.999 | 463 | 131.71 | 5.85 | 0.95 | 487.26 | 487.12 |
J2 | 1.000 | 377 | 93.55 | 5.06 | 0.92 | 387.48 | 387.40 |
J3 | 1.000 | 431 | 107.88 | 5.87 | 0.96 | 440.29 | 441.87 |
In order to reveal the differences in community composition among samples, the Beta diversity analysis was carried out (Fig. 3). The difference coefficient between J1 and J2 was the largest (1.242), followed by J1 and J3 (0.957), and then J2 and J3 (0.768). It indicated that compared with J2 and J3, J1 had a big difference in the fungal community structure, which was consistent with the cluster analysis results, indicating that the bamboo forest ecosystem had a unique fungal community structure.
Differences of soil fungal community structure and composition
The superiority communities of soil fungi in the study area were Ascomycota (relative abundance 61.21%) and Basidiomycota (37.56%) at the phylum level, and the total proportion was as high as 98.77%. The abundance of Kickxellomycota and Gloneromycota accounted for 0.8% and 0.43% respectively.
Based on the Weighted Unifrac distance matrix, two samples were compared to study the differences in fungal community composition between samples (Fig. 4). The non-bamboo forest area (J2) and the marginal area of bamboo forest (J3) were similar in soil fungal community structure, and they were grouped into one class. The difference between them and the core area of bamboo forest (J1) was great, which indicated that there was a relatively independent and unique community of soil fungi in J1. Ascomycetes were mainly distributed in J2, followed by J3, with the lowest abundance in J1. Basidiomycetes were mainly scattered in J1, that is, as the sample gradually approached the core area of bamboo forest, the dominant fungi of soil fungal community gradually changes from Ascomycetes to Basidiomycetes at the phylum level.
At the genus level (Fig. 5), the above transformation was shown by Gliocladiopsis、Ilyonectria、Cylindrocarpon、Fusarium of Ascomycetes in non-bamboo forest area (J2), transit to Fusarium、Nectria、Plectosphaerella、Pseudeurotium、Cylindrocarpon of Ascomycetes and Saitozyma of Basidiomycetes in the marginal area of bamboo forest (J3), and then Saitozyma, Laccaria, Burgoa, Auricularia, Crustoderma of Basidiomycetes and Fusarium, Cyberlindnera, Penicillium, Oidiodendron of Ascomycetes in the core area of bamboo forest (J1). In general, the fungal communities in the soil samples mostly had a common origin, and there was a certain evolutionary correlation between them at the genus level.
At the species level, the abundance of individual fungal populations had undergone significant changes, such as the unique dominant species Gliocladiopsis forsbergii (relative abundance 26.34%) and the dominant species Aspergillus niger (1.66%) of Ascomycota in the non-bamboo forest area (J2), transitioned to the unique dominant species Nectria diminuta (6.29%), Monographella nivalis (2.12%) and dominant species Thelonectria rubi (2.49%), Gibellulopsis nigrescens (1.23%) of Ascomycota in the marginal area of bamboo forest (J3), and then transformed into the dominant species Saitozyma podzolica (33.02%), Burgoa anomala (unique,3.28%) of Basidiomycota and Fusarium oxysporum (12.15%), Cyberlindnera saturnus(2.89%), Gibberella acuminata (1.23%) of Ascomycota in the core area of bamboo forest (J1) .
FunGuild function prediction
In order to further analyze the ecological function of fungal species in moso bamboo brewing forest, the function prediction of FUNGuild was carried out. According to the results demonstrated in Fig. 6, soil fungi were mainly saprophytic, symbiotic and pathological nutrition in study plots. Soil fungal functional flora in non-bamboo forest area (J2) were dominated by undefined saprophytes and unassigned fungi, followed by plant pathogen, plant pathogen-soil saprotroph-wood saprotroph, etc. Soil fungal functional flora in J2 were dominated by undefined saprophytes and unassigned fungi, followed by plant pathogen, plant pathogen-soil saprotroph-wood saprotroph, etc. As the sample gradually approached to the core area of bamboo forest, the marginal area of moso bamboo forest (J3) was dominated by unassigned fungi, and there were certain distributions of plant pathogen, undefined saprotroph, animal pathogen-endophyte-fungal parasite-lichen parasite-plant pathogen-wood saprotroph, endophyte-plant pathogen, etc. The core area of moso bamboo forest (J1) was dominated by fungal parasite-undefined saprotroph and unassigned fungi, and undefined saprotroph, ectomycorrhizal and ericoid mycorrhizal were distributed to a certain extent.