Comparison of fungal communities among ten macrophyte rhizospheres

Distribution of rhizosphere fungi of Kobresia humilis on the Qinghai-Tibet Plateau

Kobresia humilis is a major species in the alpine meadow communities of the Qinghai-Tibet Plateau (QTP); it plays a crucial role in maintaining the ecological balance of these meadows. Nevertheless, little is known about the rhizosphere fungi associated with K. humilis on the Qinghai Tibet Plateau. In this study, we used Illumina Miseq to investigate the fungal diversity, community structure, and ecological types in the root and rhizosphere soil of K. humilis across eight areas on the QTP and analyzed the correlation between rhizosphere fungi of K. humilis and environmental factors. A total of 19,423 and 25,101 operational taxonomic units (OTUs) were obtained from the roots and rhizosphere soil of K. humilis. These were classified into seven phyla, 25 classes, 68 orders, 138 families, and 316 genera in the roots, and nine phyla, 31 classes, 76 orders, 152 families, and 407 genera in the rhizosphere soil. There were 435 and 415 core OTUs identified in root and rhizosphere soil, respectively, which were categorized into 68 and 59 genera, respectively, with 25 shared genera. Among them, the genera with a relative abundance >1% included Mortierella, Microscypha, Floccularia, Cistella, Gibberella, and Pilidium. Compared with the rhizosphere soil, the roots showed five differing fungal community characteristics, as well as differences in ecological type, and in the main influencing environmental factors. First, the diversity, abundance, and total number of OTUs in the rhizosphere soil of K. humilis were higher than for the endophytic fungi in the roots by 11.85%, 9.85%, and 22.62%, respectively. The composition and diversity of fungal communities also differed between the eight areas. Second, although saprotroph-symbiotrophs were the main ecological types in both roots and rhizosphere soil; there were 62.62% fewer pathotrophs in roots compared to the rhizosphere soil. Thirdly, at the higher altitude sites (3,900-4,410 m), the proportion of pathotroph fungi in K. humilis was found to be lower than at the lower altitude sites (3,200-3,690 m). Fourthly, metacommunity-scale network analysis showed that during the long-term evolutionary process, ZK (EICZK = 1) and HY (EICHY = 1) were critical sites for development of the fungal community structure in the roots and rhizosphere soil of K. humilis, respectively. Fifthly, canonical correspondence analysis (CCA) showed that key driving factors in relation to the fungal community were longitude (R2 = 0.5410) for the root community and pH (R2 = 0.5226) for the rhizosphere soil community. In summary, these results show that K. humilis fungal communities are significantly different in the root and rhizosphere soil and at the eight areas investigated, indicating that roots select for specific microorganisms in the soil. This is the first time that the fungal distribution of K. humilis on the QTP in relation to long-term evolutionary processes has been investigated. These findings are critical for determining the effects of environmental variables on K. humilis fungal communities and could be valuable when developing guidance for ecological restoration and sustainable utilization of the biological resources of the QTP.

Bacterial Communities Associated with the Roots of Typha spp. and Its Relationship in Phytoremediation Processes

Heavy metal pollution is a severe concern worldwide, owing to its harmful effects on ecosystems. Phytoremediation has been applied to remove heavy metals from water, soils, and sediments by using plants and associated microorganisms to restore contaminated sites. The Typha genus is one of the most important genera used in phytoremediation strategies because of its rapid growth rate, high biomass production, and the accumulation of heavy metals in its roots. Plant growth-promoting rhizobacteria have attracted much attention because they exert biochemical activities that improve plant growth, tolerance, and the accumulation of heavy metals in plant tissues. Because of their beneficial effects on plants, some studies have identified bacterial communities associated with the roots of Typha species growing in the presence of heavy metals. This review describes in detail the phytoremediation process and highlights the application of Typha species. Then, it describes bacterial communities associated with roots of Typha growing in natural ecosystems and wetlands contaminated with heavy metals. Data indicated that bacteria from the phylum Proteobacteria are the primary colonizers of the rhizosphere and root-endosphere of Typha species growing in contaminated and non-contaminated environments. Proteobacteria include bacteria that can grow in different environments due to their ability to use various carbon sources. Some bacterial species exert biochemical activities that contribute to plant growth and tolerance to heavy metals and enhance phytoremediation.

Differences Between Microbial Communities of Pinus Species Having Differing Level of Resistance to the Pine Wood Nematode

The pine wood nematode (PWN), Bursaphelenchus xylophilus, is a destructive invasive species that exerts devastating effects on most native pines in invaded regions, while many of the non-native pines have resistance to PWN. Recently, increasingly more research is focused on how microbial communities can improve host resistance against pathogens. However, the relationship between the microbial community structures and varying levels of pathogen resistance observed in different pine tree species remains unclear. Here, the bacterial and fungal communities of introduced resistant pines Pinus elliottii, P. caribaea, and P. taeda and native susceptible pines healthy and wilted P. massoniana infected by PWN were analyzed. The results showed that 6057 bacterial and 3931 fungal OTUs were annotated. The pine samples shared 944 bacterial OTUs primarily in the phyla Proteobacteria, Acidobacteria, Firmicutes, Bacteroidetes, and Chloroflexi and 111 fungal OTUs primarily in phyla Ascomycota and Basidiomycota, though different pines had unique OTUs. There were significant differences in microbial community diversity between different pines, especially between the bacterial communities of resistant and susceptible pines, and fungal communities between healthy pines (resistant pines included) and the wilted P. massoniana. Resistant pines had a greater abundance of bacteria in the genera Acidothermus (class unidentified_Actinobacteria) and Prevotellaceae (class Alphaproteobacteria), but a lower abundance of Erwinia (class Gammaproteobacteria). Healthy pines had a higher fungal abundance of Cladosporium (class Dothideomycetes) and class Eurotiomycetes, but a lower abundance of Graphilbum, Sporothrix, Geosmithia (class Sordariomycetes), and Cryptoporus (classes Agaricomycetes and Saccharomycetes). These differences in microbial abundance between resistant and healthy pines might be associated with pathogen resistance of the pines, and the results of this study contribute to the studies exploring microbial-based control of PWN.

Changes in soil fungal communities after onset of wheat yellow mosaic virus disease

Rhizosphere-associated microbes have important implications for plant health, but knowledge of the association between the pathological conditions of soil-borne virus-infected wheat and soil microbial communities, especially changes in fungal communities, remains limited. We investigated the succession of fungal communities from bulk soil to wheat rhizosphere soil in both infected and healthy plants using amplicon sequencing methods, and assessed their potential role in plant health. The results showed that the diversity of fungi in wheat rhizosphere and bulk soils significantly differed post wheat yellow mosaic virus disease onset. The structure differences in fungal community at the two wheat health states or two compartment niches were evident, soil physicochemical properties (i.e., NH4 +) contribute to differences in fungal community structure and alpha diversity. Comparison analysis showed Mortierellomycetes and Dothideomycetes as dominant communities in healthy wheat soils at class level. The genus Pyronemataceae and Solicoccozyma were significantly are significantly enriched in rhizosphere soil of diseased plant, the genus Cystofilobasidium, Cladosporium, Mortierella, and Stephanonectria are significantly enriched in bulk soil of healthy plant. Co-occurrence network analysis showed that the fungi in healthy wheat soil has higher mutual benefit and connectivity compared with diseased wheat. The results of this study demonstrated that the occurrence of wheat yellow mosaic virus diseases altered both fungal community diversity and composition, and that NH4 + is the most important soil physicochemical factor influencing fungal diversity and community composition.

The Effects of Drainage on the Soil Fungal Community in Freshwater Wetlands

Wetland drainage has been intensively implemented globally, and it has exerted significant effects on wetland ecosystems. The effects of wetland drainage on the soil fungal community remain to be clarified. Soil samples were collected at depths of 0–5 and 5–10 cm in freshwater Phragmites australis wetlands to investigate changes in the fungal community before and after drainage (termed FW and DFW, respectively) using high-throughput sequencing of the fungal-specific internal transcribed spacer 1 (ITS1) gene region. No significant differences in the α diversity of the soil fungal community were found in 0–10 cm soils between FW and DFW (p > 0.05), except for the abundance-based coverage estimator (ACE) and Chao1 indices in 5–10 cm soils. Significantly higher values of ACE and Chao1 in 5–10 cm soils in FW than in DFW indicated that wetland drainage may reduce fungal community richness in 5–10 cm soils. Ascomycota, Sordariomycetes, and Cephalothecaceae were the dominant fungal phylum, class, and family, respectively, in 0–5 and 5–10 cm soils of both FW and DFW, representing as high as 76.17, 58.22, and 45.21% of the fungal community in 5–10 FW soils, respectively. Saprotrophic fungi predominated in both FW and DFW. Drainage altered both the fungal community structure and some edaphic factors. Mantel tests and Spearman correlation analyses implied that edaphic factors [i.e., soil organic matter (SOM), electronic conductivity (EC), pH, and clay] also affected soil fungal community structure. Overall, wetland drainage altered the community structure of the fungal community in the freshwater wetlands.

Denitrifying bacterial community dominantly drove nitrogen removals in vertical flow constructed wetlands as impacted by macrophyte planting patterns

The study aims to identify relations of denitrifying bacterial and fungal communities to nitrogen removals in vertical flow wetland microcosms (VFWMs) using four macrophyte species (Iris pseudacorus, Canna glauca, Scirpus validus and Cyperus alternifolius) and three species richness levels (unplanted, monocultured and 4-species mixture) as fixed factors. Results showed that among four macrophyte species, only Canna glauca planting significantly decreased nitrate removal by 87.7% in the VFWMs. The 4-species mixture improved TN and nitrate removals by 84.0% and 91.3%, but decreased ammonium removal by 94.5%. Heatmap and nonmetric multidimensional scaling analyses identified a significant difference in denitrifying bacterial community structure across macrophyte richness levels, but did not identify the difference in denitrifying fungal communities. The redundancy analysis revealed that denitrifying bacterial community individually explained 99.4% and 93.0% variance of nitrogen removals among four macrophyte species and across macrophyte richness levels, while the fungal community only explained 30.7% and 21.8% variance of nitrogen removals. Overall, the macrophyte richness and bacterial denitrifiers are the critical factors of nitrogen removals in the VFWMs, thus providing useful data to design a vertical flow constructed wetland at a full scale.

Seasonal Variation in Fungal Community Composition Associated with Tamarix chinensis Roots in the Coastal Saline Soil of Bohai Bay, China

Coastal salinity typically alters the soil microbial communities, which subsequently affect the biogeochemical cycle of nutrients in the soil. The seasonal variation of the soil fungal communities in the coastal area, closely associated with plant population, is poorly understood. This study provides an insight into the fungal community's variations from autumn to winter and spring to summer at a well-populated area of salt-tolerant Tamarix chinensis and beach. The richness and diversity of fungal community were higher in the spring season and lower in the winter season, as showed by high throughput sequencing of the 18S rRNA gene. Ascomycota was the predominant phylum reported in all samples across the region, and higher difference was reported at order level across the seasonal variations. The redundancy analysis suggested that the abundance and diversity of fungal communities in different seasons are mainly correlated to total organic carbon and total nitrogen. Additionally, the saprotrophic and pathotrophic fungi decreased while symbiotic fungi increased in the autumn season. This study provides a pattern of seasonal variation in fungal community composition that further broadens our limited understanding of how the density of the salt-tolerant T. chinensis population of the coastal saline soil could respond to their seasonal variations.

The Impact of Pine Wood Nematode Infection on the Host Fungal Community

Pine wilt disease (PWD), caused by pinewood nematode (PWN) Bursaphelenchus xylophilus, is globally one of the most destructive diseases of pine forests, especially in China. However, little is known about the effect of PWD on the host microbiome. In this study, the fungal community and functional structures in the needles, roots, and soil of and around Pinus thunbergii naturally infected by PWN were investigated by using high-throughput sequencing coupled with the functional prediction (FUNGuild). The results showed that fungal richness, diversity, and evenness in the needles of diseased trees were significantly lower than those of healthy ones (p < 0.05), whereas no differences were found in the roots and soil. Principal coordinate analysis (PCoA) showed that the fungal community and functional structures significantly differed only in the needles of diseased and healthy trees, but not in the soil and roots. Functionally, the saprotrophs had a higher abundance in the needles of diseased trees, whereas symbiotrophs abundance was higher in the needles of healthy trees (linear discriminant analysis (LDA) > 2.0, p < 0.05). These results indicated that PWN infection primarily affected the fungal community and functional structures in the needles of P. thunbergii, but not the roots and soil.

Significant alterations in soil fungal communities along a chronosequence of Spartina alterniflora invasion in a Chinese Yellow Sea coastal wetland

Plant invasion typically alters the microbial communities of soils, which affects ecosystem carbon (C) and nitrogen (N) cycles. The responses of the soil fungal communities to plant invasion along its chronosequence remain poorly understood. For this study, we investigated variations in soil fungal communities through Illumina MiSeq sequencing analyses of the fungal internal transcribed spacer (ITS) region, and quantitative polymerase chain reaction (qPCR), along a chronosequence (i.e., 9-, 13-, 20- and 23-year-old) of invasive Spartina alterniflora. We compared these variations with those of bare flat in a Chinese Yellow Sea coastal wetland. Our results highlighted that the abundance of soil fungi, the number of operational taxonomic units (OTUs), species richness, and Shannon diversity indices for soil fungal communities were highest in 9-year-old S. alterniflora soil, which gradually declined along the invasion chronosequence. The relative abundance of copiotrophic Basidiomycota revealed significant decreasing trend, while the relative abundance of oligotrophic Ascomycota gradually increased along the S. alterniflora invasion chronosequence. The relative abundance of soil saprotrophic fungi (e.g., undefined saprotrophs) was gradually reduced while symbiotic fungi (e.g., ectomycorrhizal fungi) and pathotrophic fungi (e.g., plant and animal pathogens) progressively increased along the S. alterniflora invasion chronosequence. Our results suggested that S. alterniflora invasion significantly altered soil fungal abundance and diversity, community composition, trophic modes, and functional groups along a chronosequence, via substantially reduced soil litter inputs, and gradually decreased soil pH, moisture, and soil nutrient substrates along the invasion chronosequence, from 9 to 23 years. These changes in soil fungal communities, particularly their trophic modes and functional groups along the S. alterniflora invasion chronosequence could well impact the decomposition and accumulation of soil C and N, while potentially altering ecosystem C and N sinks in a Chinese Yellow Sea coastal wetland.