Plant community characteristics in different experimental plots
Table 2
Species composition of plant communities at differential experimental plot
sampling site code | Herbaceous dominant species | Species number | Species of top 5 importance value |
CK | - | 11 | Artemisia selengensis(18.71), Oenanthe javanica(14.38), Polygonum hydropiper(12.08), Rorippa indica(10.63), Cardamine hirsuta(9.07) |
AS | Artemisia selengensis | 14 | Artemisia selengensis(30.44), Trigonotis peduncularis(7.11), Phragmites australis(6.73), Mazus pumilus(6.46), Polygonum hydropiper(6.30) |
CX | Carex brevicuspis, Carex dispalata | 22 | Carex brevicuspis(17.70), Carex dispalata(15.84), Polygonum hydropiper(7.05), Miscanthus lutarioriparius(6.11), Galium spurium(6.07) |
As shown in Table 2, the dominant species of plant communities differed among the three experimental plots. There were 22 species in the Carex spp. community; Carex brevicuspis and Carex dispalata were the dominant species and Polygonum hydropiper, Miscanthus lutarioriparius, and Galium spurium were the associated species in the community. There were 14 kinds of plants in the A. selengensis community; among them, Artemisia selengensis was the most significant and constructive species, and Trigonotis peduncularis, Phragmites australis, Mazus pumilus were associated species. There were 11 kinds of herbaceous plants in the control plot, among which Artemisia selengensis, Polygonum hydropiper, Oenanthe javanica, Rorippa indica, and Cardamine hirsuta were key understory species, but there were no discernable dominant herbaceous species.
Physical And Chemical Properties Of Soil From Different Plant Communities
Table 3
Physical and chemical properties of Soil from different plant communities
index | CK | AS | CX |
water content (%) | 24.23 ± 0.68c | 29.95 ± 1.71b | 38.50 ± 2.12a |
Bulk density (g·cm-3) | 1.39 ± 0.03a | 1.31 ± 0.10a | 1.02 ± 0.07b |
Clay (%) | 3.27 ± 0.07b | 3.41 ± 0.20b | 3.86 ± 0.11a |
Silt (%) | 90.23 ± 0.54a | 90.27 ± 0.44a | 90.55 ± 1.14a |
Gravel (%) | 6.50 ± 0.60a | 6.32 ± 0.62a | 5.59 ± 1.23a |
Porosity (%) | 38.29 ± 0.61a | 28.89 ± 5.10b | 30.76 ± 0.96b |
Catalase activity (U·g-1) | 4.72 ± 0.24b | 5.81 ± 0.43a | 5.92 ± 0.24a |
pH value | 6.56 ± 0.09a | 6.24 ± 0.13b | 6.40 ± 0.12ab |
electrical conductivity (uS·cm-1) | 23.00 ± 0.50c | 38.10 ± 1.57b | 46.57 ± 3.13a |
total nitrogen (g·kg-1) | 1.10 ± 0.04b | 1.16 ± 0.04b | 1.40 ± 0.04a |
Ammonium nitrogen (mg·kg-1) | 0.24 ± 0.03a | 0.35 ± 0.07a | 0.26 ± 0.13a |
Nitrate nitrogen (mg·kg-1) | 0.78 ± 0.01b | 1.06 ± 0.28ab | 1.32 ± 0.17a |
Total phosphorus (g·kg-1) | 0.56 ± 0.01b | 0.60 ± 0.04b | 0.74 ± 0.09a |
Available phosphorus (mg·kg-1) | 7.20 ± 1.21b | 16.23 ± 2.58a | 20.40 ± 2.53a |
Organic matter (g·kg-1) | 14.27 ± 0.17b | 19.77 ± 2.16a | 21.13 ± 0.82a |
Note: The data in the table were mean standard deviation, and different lowercase letters indicate significant differences. |
All three experimental plots had acidic soils (Table 3), with pH values ranging from 6.24 to 6.56. Moreover, soil EC ranged from 23.00 to 46.57 (uS·cm− 1). The soil particle size composition was primarily silt, accounting for 90.23–90.55% of the total soil.
The soil of the Carex spp. community had the highest WC, oproportion of clay(CY), proportion of silt, CAT, EC, TN, NN, TP, AP, and OM content, followed by the A. selengensis community, and those in the control plot, had the lowest. Conversely, soil BK and the proportion of gravel in the control were the highest, followed by the soil of A. selengensis community, then that of the Carex spp. community (the lowest). The soil PV and pH value of the control were the highest, followed by the Carex spp. community, and were the lowest in the A. selengensis community. The AN content in soil was the highest in the A. selengensis community, followed by the Carex spp. community, and was the lowest in the control.
The soil BK and pH value were lower in A. selengensis and Carex spp. communities, whereas soil WC, CY, EC, TN, and OM content were higher, soil nutrient content was elevated, and soil water storage capacity as well as environmental quality were improved, compared with the control.
Structure Of Rhizosphere Microbial Communities In Different Plant Communities
Effective sequencing data
After sequencing, 45,314 optimized fungal sequences were obtained in rhizosphere soil of the three experimental plots. Based on sequence similarities of 97.00%, they were divided into 1,979 fungal OTUs, including 15 phyla, 53 classes, 127 orders, 254 families, 465 genera, and 679 species. We obtained a 23,609 optimized bacterial gene sequences, which could be divided into 3,950 bacterial OTUs, including 47 phyla, 141 classes, 317 orders, 478 families, 777 genera, and 1,526 species.
As shown in Fig. 2, there were 169 fungi OTUs in rhizosphere soil shared by the three experimental plots, 108 OTUs shared by the control and A. selengensis community, 105 OTUs shared by the control and Carex spp. community, and 152 OTUs shared by the A. selengensis and Carex spp. communities. Among the three experimental plots, the Carex spp. community had the greatest number of unique OTUs (582). The number of unique OTUs in the A. selengensis community (431) was nearly identical to that in the control (432). In the rhizosphere soil of the three experimental plots, there were 1,481 bacteria OTUs, 342 of which were shared with the control and A. selengensis community, 629 with the control and Carex spp. community, and 278 with the A. selengensis and Carex spp. communities. Among the three experimental plots, the control had the largest number of unique OTUs (522), followed by the of Carex spp. community (384), and the A. selengensis community (314).
To summarize, the number of OTUs of rhizosphere microorganisms varied between experimental plots. Among the three experimental plots, the largest number of fungal OTUs in rhizosphere soil was from the Carex spp. community with 1,008 OTUs, followed by the A. selengensis community with 860 OTUs, and the lowest was in the control with 814 OTUs. However, the control had the most bacterial OTUs in the rhizosphere soil (2,974), followed by the Carex spp. community (2,772) and the A. selengensis community (2,415).
Abundance And Diversity Of Microbial Communities In Rhizosphere Soil
Table 4
Alpha index of rhizosphere soil microbial community (OTU level)
| sampling site code | Chao index | Shannon index |
fungi | CK | 391.66 ± 66.59 | 4.19 ± 0.08 |
AS | 464.67 ± 75.99 | 3.64 ± 0.37 |
CX | 482.31 ± 74.08 | 4.33 ± 0.43 |
bacteria | CK | 2653.73 ± 20.08 | 6.51 ± 0.10 |
AS | 2139.68 ± 37.42 | 5.89 ± 0.08 |
CX | 2256.67 ± 211.52 | 5.92 ± 0.47 |
Note: The data in the table were mean standard deviation. |
In this study, the Chao index was employed to assess the richness of microbial communities in rhizosphere soil samples; the higher the Chao index, the higher the richness of microbial communities. The Shannon index was used to determine the diversity of microbial communities in the rhizosphere soil samples; the lower the Shannon index, the lower the diversity of microbial communities.
The findings revealed that the richness and diversity of rhizosphere microbial communities differed significantly amongst the three experimental plots (Table 4). Among them, the richest and most diverse fungal community was in the rhizosphere soil of the Carex spp. community. The richness of fungal community in the rhizosphere soil of the A. selengensis community was greater than that of the control, but the diversity of was lower. Among the three communities, however, the control had the most rich and diverse rhizosphere bacterial communities.
Species Composition Of Fungal And Bacterial Communities
The bacterial and fungal species composition (from phylum, family, genus, to OTU level) in the rhizosphere soil of the three experimental plots was investigated to determine the relationship between underground microbial communities and aboveground plant communities. There were also Unclassified (sequence without classification information in the database) and Norank (in the middle level of the taxonomic pedigree of the database but was not named yet).
Figure 3A analyzes the composition of fungal communities (at the phylum level) in the rhizosphere soil of the three experimental plots. The dominant fungal phyla were Ascomycota (48.22–65.27%) and Basidiomycota (21.27–36.01%), followed by Rozellomycota (0.73–7.08%), Mortierellomycota (1.42–3.95%), Glomeromycota (0.31–3.45%), Chytridiomycota (0.53–2.16%), and some unclassified_k_Fungi (7.12–8.38%). Ascomycota were the most abundant in the rhizosphere soil of the Carex spp. community, followed by those in the control plot, and the least abundant was in that of the A. selengensis community. Basidiomycota, Glomeromycota, and Chytridiomycota were the most abundant in the A. selengensis community, followed by the control plot, and were the least abundant in the Carex spp. community. The control plot had the highest concentration of Rozellomycota, followed by the Carex spp. community, while the A. selengensis community had the lowest concentration. Mortierellomycota abundance was highest in the control, followed by that in the A. selengensis community, and it was the lowest in the rhizosphere soil of the Carex spp. community.
The dominating rhizosphere fungi in the three experimental plots were substantially different at the genus level (Fig. 3C). The genera with the highest abundance in the control plot were ranked as follows: Saitozyma (8.84%), Inocybe (5.44%), Emericelopsis (4.75%), Cladosporium (4.04%), Penicillium (3.74%), and Mortierella (3.68%), with a total relative abundance of 30.49%. In the rhizosphere soil of the Carex spp. Community, Limonomycetes (8.56%), Talaromyces (7.85%), Apiospora (4.38%), Fusarium (3.55%), Cladosporium (3.4%), and Paraphaeosphaeria (3.3%) were the most abundant, with a total relative abundance of 31.04%. The unclassified_c_Agaricomycetes (Agaricomycetes) (14.96%), Paraphoma (3.63%), Talaromyces (9.2%), Didymella (4.9%), Saitozyma (4.54%), and Emericelopsis (3.06%) had the highest relative abundance in the rhizosphere soil of the A. selengensis community, with a total relative abundance of 40.29%.
The dominant phyla in the bacterial communities in the rhizosphere soil of the three experimental plots (Fig. 3B), were Proteobacteria (20.82–23.86%), Actinobacteriota (13.28–28.91%), Acidobacteriota (13.64–22.07%) and Chloroflexi (11.89–17.65%), followed by Methylomirabilota (1.01–4.56%), Myxococcota (3.29–4.27%), Verrucomicrobiota (0.37–1.85%), Desulfobacterota (1.54–2.85%), Bacteroidea (1.3–2.97%), Nitrospirota (0.97–2.07%), Latescibacterota (0.65–1.2%), Firmicutes (1.89–7.47%), and Gemmatimonadota (2.11–6.38%). Among these, Verrucomicrobiota and Desulfobacterota are more relatively abundant in the rhizosphere soil of the Carex spp. Community. Proteobacteria and Firmicutes had the largest abundance in the rhizosphere soil of the A. selengensis community, followed by that of the Carex spp. Community, and were the least abundant in the control plot. The abundance of Actinobacteriota and Gemmatimonadota in the rhizosphere soil of the Carex spp. Community was the highest, followed by that of the control, and the lowest was in the of A. selengensis community. The abundance of Acidobacteriota was the highest in the rhizosphere soil of the A. selengensis community, followed by that in the control plot, and the lowest was in the Carex spp. community rhizosphere soil; The abundance of Chloroflexi in the rhizosphere soil of control was the highest, then that of the A. selengensis community rhizosphere soil, the lowest was in the rhizosphere soil of the Carex spp. community; Nitrospirota was most abundant in the control plot, followed by the Carex spp. Community and A. selengensis community.
The dominant rhizosphere bacteria in the three experimental plots were also different at the family level (Fig. 3D, excluding unclassified families). Xanthobacteraceae (6.71%), Gemmatimonadaceae (4.44%), Roseiflexaceae (2.89%), Streptomycetaceae (2.42%), and Gaiellaceae (2.1%) had the highest relative abundance in the control plot; overall relative abundance was 18.56%. Nocardioidaceae (13.67%), Gemmatimonadaceae (6.29%), Xanthobacteraceae (5.72%), and Sphingomonadaceae (2.25%) were abundant in the rhizosphere soil of Carex spp. community, accounting for 27.93% of the overall relative abundance. The rhizosphere bacteria with the highest abundance in the A. selengensis community rhizosphere soil were Xanthobacteraceae (10.3%), Bacillaceae (3.96%), Methyloligellaceae (2.91%), Anaerolineaceae (2.59%), Solibacteraceae (2.5%), and Gemmatimonadaceae (2.05%), with a total relative abundance of 24.31%.
The closer the points on the principal coordinate analysis (PCoA) diagram are to one another, the more similar the species composition of the communities. As shown in Fig. 4, the PCoA results indicated that the contribution rates of the first axes of fungi and bacteria were 23.11% and 38.94%, and that the contribution rates of the second axes were 20.74% and 23.92%. At the OTU level, there were significant differences in the species composition of the microbial community among the three plant communities; however, the variation in microbial community composition of the same plant community at different sampling sites was not significant.
Overall, the results demonstrated that the composition of microbial communities in rhizosphere soil of the three experimental plots differed significantly at the genus, family, and OTU levels, despite having similar phyla. The dominant phyla of rhizosphere fungal communities of the three experimental plots were Ascomycota and Basidiomycota. The total relative abundance of Basidiomycota and Ascomycota in the Carex spp. community were the highest (86.54%), followed by the A. selengensis community (84.23%), and the control plot (79.06%). Proteobacteria, Actinobacteriota, Acidobacteriota, and Chloroflexi were the dominant phyla of rhizosphere bacterial communities in the three experimental plots. The total relative abundance of Proteobacteria, Actinobacteriota, Acidobacteriota, and Chloroflexi was highest (75.42%) in the Carex spp. community, followed by the control (74.54%), and lowest in the A. selengensis community (73.32%).
Redundancy Analysis Of Rhizosphere Microbial Community Distribution And Soil Physicochemical Properties
Table 5
Relationship between rhizosphere microbial community abundance and soil environmental factors
| environmental factor | correlation coefficient |
Axis 1 | Axis 2 |
fungi | NN | 0.9236 | -0.3834 |
AN | -0.9885 | 0.1511 |
AP | -0.0992 | -0.9951 |
OM | -0.6553 | -0.7554 |
pH | 0.6787 | 0.7344 |
CY | 0.9772 | -0.2124 |
bacteria | NN | -0.2022 | 0.9793 |
AN | -0.2986 | 0.9544 |
OM | -0.0331 | 0.9995 |
WC | -0.7644 | 0.6448 |
PV | -0.2585 | -0.966 |
CY | -0.9261 | 0.3772 |
Note:NN:Nitrate nitrogen; AN:Ammonium nitrogen; AP:Available phosphorus; OM:Organic matter; CY:Clay |
PV:porosity; WC:Water content
Redundancy analysis (RDA) of microbial communities (at the phylum level) and major soil factors was conducted to investigate the relationship between microbial communities and soil properties (see Fig. 5 and Table 5). Considering the rhizosphere fungal community (Fig. 5A), Ascomycota was positively correlated with soil pH value, CY, and NN content, and negatively correlated with AN and OM content. In contrast, Basidiomycota was positively correlated with AN, OM, and AP content, and negatively correlated with NN content and pH value. In general, the key soil factors that affect rhizosphere fungal community differences were AN, NN, OM content, pH value, and CY.
Acidobacteriota was positively correlated with OM, and negatively correlated with PV, CY, and WC in the rhizosphere bacterial community (Fig. 5B). Similarly, Proteobacteria was positively correlated with soil OM content and negatively correlated with soil WC and CY. In contrast, Actinobacteriota were positively correlated with PV, CY, AN, NN, and OM content. Chloroflexi was positively correlated with PV and negatively correlated with WC, CY, OM, NN, and AN content. Overall, the key soil factors that caused differences in bacterial community structure were PV, CY, OM, and NN content. Moreover, CY, OM, AN, and NN content were the main soil factors that were behind the differences in the structure and composition of rhizosphere microbial communities in the soil of various plant communities.