Protist Community Composition Research Articles

Response of protists to nitrogen addition, arbuscular mycorrhizal fungi manipulation, and mesofauna reduction in a tropical montane rainforest in southern Ecuador.

The tropical Andes are a species-rich and nitrogen-limited system, susceptible to increased nitrogen (N) inputs from the atmosphere. However, our understanding of the impacts of increased N input on belowground systems, in particular on protists and their role in nutrient cycling, remains limited. We explored how increased N affects protists in tropical montane rainforests in Ecuador using high-throughput sequencing (HTS) of environmental DNA from two litter layers. In addition, we manipulated the amount of arbuscular mycorrhizal fungi (AMF) and mesofauna, both playing a significant role in N cycling and interacting in complex ways with protist communities. We found that N strongly affected protist community composition in both layers, while mesofauna reduction had a stronger effect on the lower layer. Changes in concentration of the AMF marker lipid had little effect on protists. In both layers, the addition of N increased phagotrophs and animal parasites and decreased plant parasites, while mixotrophs decreased in the upper layer but increased in the lower layer. In the upper layer with higher AMF concentration, mixotrophs decreased, while in the lower layer, photoautotrophs increased and plant parasites decreased. With reduced mesofauna, phagotrophs increased and animal parasites decreased in both layers, while plant parasites increased only in the upper layer. The findings indicate that to understand the intricate response of protist communities to environmental changes, it is critical to thoroughly analyze these communities across litter and soil layers, and to include HTS.

Phosphorus Fertilization Boosts Mineral-Associated Soil Organic Carbon Formation Associated with Phagotrophic Protists.

Long-term fertilization affects soil organic C accumulation. A growing body of research has revealed critical roles of bacteria in soil organic C accumulation, particularly through mineral-associated organic C (MAOC) formation. Protists are essential components of soil microbiome, but the relationships between MAOC formation and protists under long-term fertilization remain unclear. Here, we used cropland soil from a long-term fertilization field trial and conducted two microcosm experiments with 13C-glucose addition to investigate the effects of N and P fertilizations on MAOC formation and the relationships with protists. The results showed that long-term fertilization (especially P fertilization) significantly (P < 0.05) increased 13C-MAOC content. Compared with P-deficient treatment, P replenishment enriched the number of protists (mainly Amoebozoa and Cercozoa) and bacteria (mainly Acidobacteriota, Bacteroidota, and Gammaproteobacteria), and significantly (P < 0.001) promoted the abundances of bacterial functional genes controlling C, N, P, and S metabolisms. The community composition of phagotrophic protists prominently (P < 0.001) correlated with the bacterial community composition, bacterial functional gene abundance, and 13C-MAOC content. Co-occurrence networks of phagotrophic protists and bacteria were more connected in soil with the N inoculum added than in soil with the NP inoculum added. P replenishment strengthened bacterial 13C assimilation (i.e., 13C-phospholipid fatty acid content), which negatively (P < 0.05) correlated with the number and relative abundance of phagotrophic Cercozoa. Together, these results suggested that P fertilization boosts MAOC formation associated with phagotrophic protists. Our study paves the way for future research to harness the potential of protists to promote belowground C accrual in agroecosystems.

An examination of protist diversity in serpentinization-hosted ecosystems of the Samail Ophiolite of Oman.

In the Samail Ophiolite of Oman, the geological process of serpentinization produces reduced, hydrogen rich, hyperalkaline (pH > 11) fluids. These fluids are generated through water reacting with ultramafic rock from the upper mantle in the subsurface. On Earth's continents, serpentinized fluids can be expressed at the surface where they can mix with circumneutral surface water and subsequently generate a pH gradient (∼pH 8 to pH > 11) in addition to variations in other chemical parameters such as dissolved CO2, O2, and H2. Globally, archaeal and bacterial community diversity has been shown to reflect geochemical gradients established by the process of serpentinization. It is unknown if the same is true for microorganisms of the domain Eukarya (eukaryotes). In this study, using 18S rRNA gene amplicon sequencing, we explore the diversity of microbial eukaryotes called protists in sediments of serpentinized fluids in Oman. We demonstrate that protist community composition and diversity correlate significantly with variations in pH, with protist richness being significantly lower in sediments of hyperalkaline fluids. In addition to pH, the availability of CO2 to phototrophic protists, the composition of potential food sources (prokaryotes) for heterotrophic protists and the concentration of O2 for anaerobic protists are factors that likely shape overall protist community composition and diversity along the geochemical gradient. The taxonomy of the protist 18S rRNA gene sequences indicates the presence of protists that are involved in carbon cycling in serpentinized fluids of Oman. Therefore, as we evaluate the applicability of serpentinization for carbon sequestration, the presence and diversity of protists should be considered.

有机肥施用对红壤原生生物与微生物互作的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 有机肥施用对红壤原生生物与微生物互作的影响 DOI: 10.5846/stxb202112253651 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家优秀青年基金（41922048）；国家面上基金（42107336，42177298） Impacts of manure application on interaction between protists community and microorganisms in red soil Author: Affiliation: Fund Project: National Science Fund for Excellent Young Scholars of China (41922048), National Natural Science Foundation of China (42177298, 42107336) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为明确不同施肥处理对土壤原生生物群落、微生物碳代谢活性的影响，以南方典型旱地红壤为研究对象，基于中国科学院鹰潭红壤生态实验站玉米单作系统有机培肥长期定位试验，选取不施肥（M0）、低量猪粪（M1）、高量猪粪（M2）、高量猪粪+石灰（M3）4个处理，利用高通量测序技术研究不同猪粪处理下红壤原生生物多样性、群落结构的变化，揭示原生生物与微生物互作对土壤微生物碳代谢活性和玉米产量的影响。结果表明：①长期施用猪粪处理下，土壤pH、有机质（SOM）、全氮（TN）、全磷（TP）、速效磷（AP）和速效钾（AK）的含量显著提高；②与M0处理相比，施肥处理显著提高了原生生物生物量和多样性，并且显著改变了其群落结构，其中土壤TP、pH、AP、TN、SOM和AK是原生生物群落结构变化的重要驱动因子；③施肥处理显著提高了土壤细菌和真菌生物量，增加了微生物碳代谢活性（Average well color development，AWCD）；④土壤pH和AP通过影响原生生物多样性和群落结构，间接提高了微生物碳代谢活性和玉米产量。本研究结果为提升旱地红壤的生物多样性，保障土壤健康和维持生态系统服务功能提供了科学依据。 Abstract:The purpose of this study was to investigate the protist community and soil microbial carbon metabolism with pig manure application in the dryland red soil of south China. The long-term field experiment was conducted in maize mono-cropping system at the National Agro-Ecosystem Observation and Research Station in Yingtan, Jiangxi Province. Four treatments included no manure (M0), low manure (M1), high manure (M2), and high manure with lime addition (M3). The high-throughput sequencing of 18S rRNA gene was used to explore the diversity and structure of soil protist community, and to estimate the effect of protists-microorganisms interaction on microbial carbon metabolism and maize yield. Our results showed that soil chemical properties significantly varied under the four fertilization treatments. Soil pH, soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), and available potassium (AK) were significantly increased under manure treatments. Compared with M0 treatment, manure treatments (M1, M2, and M3) significantly enhanced the biomass and diversity of protist, and remarkably modified the protist community structure. The protist community composition was mainly affected by soil TP, pH, AP, TN, SOM, and AK. Manure application significantly improved the bacterial and fungal biomasses, and consequently promoted microbial carbon metabolism indicated by the values of average well color development (AWCD). Structural equation modelling indicated that soil pH and AP could indirectly increase microbial carbon metabolism and maize yield through regulating the diversity and structure of protist community. Taken together, we provide the scientific basis for promoting the microbial diversity in the dryland red soil, and maintaining soil health and ecosystem service functioning. 参考文献 相似文献 引证文献

Exploring the diversity of microeukaryotic communities in New England tide pools

Though historically understudied, due in large part to most species being uncultivable, microbial eukaryotes (i.e. protists) are abundant and widespread across diverse habitats. Recent advances in molecular techniques, including metabarcoding, allow for the characterization of poorly known protist lineages. This study surveys the diversity of SAR (Stramenopila, Alveolata, and Rhizaria), a major eukaryotic clade that is estimated to represent about half of all eukaryotic diversity. SAR lineages use varied metabolic strategies like mixotrophy in dinoflagellates (Alveolata), parasitism in apicomplexans (Alveolata) and labyrinthulids (Stramenopila), and life cycle stages that include encystment and attachment (e.g. in ciliates, Alveolata) to survive in highly dynamic habitats. Using metabarcoding primers designed specifically to target a portion of the 18S small subunit ribosomal RNA (SSU-rRNA) gene of SAR lineages, we compare protist community composition from tide pools in Acadia National Park, Maine, USA. We characterize over 500 lineages, here operational taxonomic units (OTUs), many of which are found abundant in the tide pool environment. We also find that communities vary by month sampled and exhibit patterns by size (i.e. macro-, micro-, and nano-sized). Taken together, these data allow us to further catalog protist diversity in extreme environments (e.g. those subject to extreme fluctuations in temperature and salinity during tidal cycles). Such data are critical in the explorations of biodiversity patterns among microorganisms on our rapidly changing planet.

Taxonomic Composition of Protist Communities in the Coastal Stratified Lake Kislo-Sladkoe (Kandalaksha Bay, White Sea) Revealed by Microscopy

Lake Kislo-Sladkoe is a stratified water body partly isolated from the White Sea. Perennial meromixis in the lake irregularly alternates with mixing events. Taking into account that the protists of Arctic coastal stratified water bodies are understudied, we evaluated for the first time the vertical structure, species richness, and diversity of protists assigned to different taxonomic groups in Lake Kislo-Sladkoe using light, luminescent, and scanning electron microscopy. To test the research hypothesis that a mixing event affects the vertical stratification and species composition of protists in a stratified lake, we compared the protist communities of Lake Kislo-Sladkoe in two extremely different states: strong meromixis vs. full vertical mixing. A total of 97 morphologically distinct phototrophic, heterotrophic, and mixotrophic protists were revealed with the most diverse supertaxa SAR (59), Obazoa (9), and Excavates (14). The hidden diversity of protists (43 species) was a bit less than the active diversity (54 species). A taxonomic list and micrographs of cells for the observed protists are provided. The majority of species revealed are cosmopolitan or widespread in the northern sea waters. The vertical patterns of protist communities were absolutely different in 2018 and 2021. In July 2018, clearly distinct protist communities inhabited different layers of the lake. Bloom of cryptophyte Rhodomonas cf. baltica was detected in chemocline, whereas the maximum density of its grazers was observed in adjacent layers, mainly dinoflagellates Gymnodinium sp. and Scrippsiella trochoidea, as well as a ciliate Prorodon sp. In 2021 due to the recent mixing of lake and seawater, there were no distinct communities in the water column except the superficial 0–1 m layer of fresh water.

Trophic State Drives the Diversity of Protists in a Tropical River (New River, Belize).

Land use disrupts the ecosystem functioning of freshwater systems and significantly affects trophic state. Consequently, biodiversity is severely affected by changes to the ecosystem. Microbial eukaryotes (i.e., protists) play an essential role in ecosystem functioning, contributing to biogeochemical processes, nutrient cycling, and food webs. Protist composition is a useful biological quality parameter for monitoring aquatic ecosystems and determining aquatic system health. In this study, we investigated the effects of land usage and trophic state on the communities of microbial eukaryotes in the New River (Belize, C.A.). Land use and trophic state both significantly affected protist community compositions, with impacted and mesotrophic sampled sites having higher biodiversity when compared to other sites. Autotrophic organisms dominated indirectly impacted and eutrophic sites, while impacted and mesotrophic sites had proportional ratios of autotrophic and heterotrophic organisms. Our study highlights the significant effects of trophic gradients on protistan community composition, even at the local scales.

Fertilization drives distinct biotic and abiotic factors in regulating functional groups of protists in a 5-year fertilization system.

Protists play an important role in nutrient cycling, microbiome stability and soil fertility maintenance. However, the driving force of protistan functional groups remains poorly understood in agricultural ecosystems. We investigated the impacts of fertilization regimes on the diversity, composition and functional groups of protists and further disentangled the effects of multiple factors shaping the community composition of functional groups in a 5-year fertilization regime (CK, no fertilization; M, organic fertilization; MNPK, combined inorganic and organic fertilization; NPK, inorganic fertilization). Fertilization significantly changed the community composition of protists rather than diversity. The MNPK treatment significantly increased the relative abundance of phototrophs and decreased that of the parasites and consumers. Partial least squares path modeling indicated that fertilization indirectly regulated protistan consumers via changes in the P content, which affected the composition of consumers mainly by regulating fungal community composition. Soil moisture (SM) and available phosphorus (AP) were identified as the top predictors for the composition of parasites, and the composition of phototrophs was mainly affected by SM, indicating that parasites and phototrophs were more sensitive to abiotic factors in the fertilization system. Taken together, our findings highlight that fertilization significantly affects the composition of functional groups of protists and their biotic or abiotic regulatory processes, which have implications for the potential changes in their ecosystem functions for soil management systems.

Rubble fields shape planktonic protist communities in Indonesia at a local scale.

The Coral Triangle encompasses nearly 30% of the world's coral reefs and is widely considered the epicenter of marine biodiversity. Destructive fishing practices and natural disturbances common to this region damage reefs leaving behind fields of coral rubble. While the impacts of disturbances in these ecosystems are well documented on metazoans, we have a poor understanding of their impact on microbial communities at the base of the food web. We use metabarcoding to characterize protist community composition in sites of varying fisheries management schemes and benthic profiles across the island of Lombok, Indonesia. Our study shows that rubble coverage and net primary productivity are the strongest explainers of variation in protist communities across Lombok. More specifically, rubble fields are characterized by increases in small heterotrophic protists, including ciliates and cercozoans. In addition to shifts in heterotrophic protist communities, we also observed increases in diatom relative abundance in rubble fields, which corresponded to sites with higher net primary productivity. These results are the first to characterize protist communities in tropical marine rubble fields and provide insight on environmental factors potentially driving these shifts on a local scale.

Seasonal variation in the community distribution of protists off Wakasa Bay, Southern Sea of Japan

There is a dearth of knowledge regarding the spatiotemporal distribution of protistan community composition and seasonal environmental changes. High-throughput sequencing of the 18S rRNA gene was performed to assess changes in the community composition of protists over four seasons at four sites in Wakasa Bay, located in the center of Japan's northern coast. The community composition varied seasonally rather than geographically, even among few local communities confined to the bay head. Throughout the year, Alveolata and Chlorophyta were widely distributed and represented the predominant groups. Groups I and II of Syndiniales and Dinoflagellata were significant taxa in terms of operational taxonomic unit richness and sequence read abundance. Although three lineages of prasinophyte Clade VII, Pycnococcus-related prasinophyte, and Ostreococcus-related Mamiellophyceae were common, prasinophyte Clade VII was dominant during summer–autumn, whereas others were dominant during winter and spring. These results indicate the differential dominance of Chlorophyta at the intrataxon level. In the protistan community, increased temperature exerted an effect on the summer–autumn composition, whereas increased nitrate concentration showed an effect on the winter composition, suggesting that seasonal environmental changes affect the protistan community composition with different fluctuation patterns being observed among taxa.

Spatiotemporal distribution of protists in the Yarlung Zangbo River, Tibetan Plateau

Protists, which include eukaryotic algae and protozoa, are crucially important for biogeochemical cycling and the aquatic food web but are sensitive to environmental fluctuations. Despite investigations in the 1970s, protist diversity and biogeographic characteristics in the Tibetan Plateau are poorly understood. Within the framework of a regional survey of protist diversity, we used high-throughput amplicon sequencing to investigate the composition and spatiotemporal turnover of protist communities along the Yarlung Zangbo River, a representative aquatic habitat of the Tibetan Plateau. In total, we detected 9,959 amplicon sequence variants in protist communities along the river and associated lakes and wetlands. The alpha diversity of protists was highest in spring and declined in the autumn. Moreover, alpha diversity was much higher in the middle and upstream reaches and tributaries than in the connected lakes and wetlands. We discovered spatiotemporal heterogeneity in the composition of protist communities across the seasons. Bacillariophyta predominated in protist communities in cold seasons (spring and autumn) and colder (high-altitude) areas, whereas Ciliophora and Cercozoa species predominated in the warm season (summer) and warmer (low-altitude) areas. Of the environmental factors, altitude, turbidity and salinity correlated with spatiotemporal dissimilarities among protist communities. The breadth of the habitat niche was restricted by turbidity and altitude in river areas and by salinity in lake and wetland areas. Co-occurrence network analysis suggested that protist communities in the Yarlung Zangbo River were substantially more complex in the warm season than in the cold seasons, and that amplicon sequence variants belonging to Ochrophyta, Chlorophyta, and Ciliophora contributed greatly to the stability of the co-occurrence network. In summary, this study provides a comprehensive overview of the spatiotemporal dynamics of protist diversity in the Yarlung Zangbo River and improves our understanding of the environmental adaptation of protists living in aquatic habitats of the Tibetan Plateau.

Planktonic protist diversity across contrasting Subtropical and Subantarctic waters of the southwest Pacific

Planktonic protists are an essential component of marine pelagic ecosystems where they mediate important trophic and biogeochemical functions. Although these functions are largely influenced by their taxonomic affiliation, the composition and spatial variability of planktonic protist communities remain poorly characterized in vast areas of the ocean. Here, we investigated the diversity of these communities in contrasting oceanographic conditions of the southwest Pacific (33–58 °S) using DNA metabarcoding of the 18S rRNA gene. Seawater samples collected during twelve cruises (n = 482, 0–3100 m) conducted east of New Zealand were used to characterize protist communities in Subtropical (STW) and Subantarctic (SAW) surface water masses and the Subtropical Front (STF) that separates them. Diversity decreased with increasing latitude and increasing temperature but tended to be lowest in the STF. Sample ordination resulting from the abundance of amplicon single variants (ASVs) corresponded to the different water masses. Overall, Dinoflagellata (Syndiniales, 27%; Dinophyceae, 24% of standardized number of reads) dominated the euphotic zone followed by Chlorophyta (20%), but their relative abundance and composition at class and lower taxonomic levels varied consistently between water masses. Among Chlorophyta, several picoplanktonic algae species of the Mamiellophyceae class including Ostreococcus lucimarinus dominated in STW, while the Chloropicophyceae species Chloroparvula pacifica was most abundant in SAW. Bacillariophyta (5%), Prymnesiophyceae (5%), and Pelagophyceae (2%) classes were less abundant but showed analogous water mass specificity at class and finer taxonomic levels. Protist community composition in the STF had mixed characteristics and showed regional differences with the southern STF (50 °S) having more resemblance with subantarctic communities than the STF over the Chatham Rise region (42–44 °S). Below the euphotic zone, Syndiniales sequences (40%) dominated the dataset followed by Radiolaria (31%), Dinophyceae (14%) and other heterotrophic groups like Marine Stramenopiles and ciliates (1–1.5%). Among Radiolaria, several unidentified ASVs assigned to Spumellaria were most abundant, but showed significantly different distributions between STW and SAW highlighting the need to further investigate the taxonomy and ecology of this group. The present study represents a significant step forward towards characterizing protistan communities composition in relation to major physical oceanographic features in the southwest Pacific providing new insights about the biogeography and ecological preferences of different planktonic protist taxa from class to species and genotypic level.

Availability of vitamin B12 and its lower ligand intermediate α-ribazole impact prokaryotic and protist communities in oceanic systems

Genome analyses predict that the cofactor cobalamin (vitamin B12, called B12 herein) is produced by only one-third of all prokaryotes but almost all encode at least one B12-dependent enzyme, in most cases methionine synthase. This implies that the majority of prokaryotes relies on exogenous B12 supply and interacts with producers. B12 consists of a corrin ring centred around a cobalt ion and the lower ligand 5’6-dimethylbenzimidazole (DMB). It has never been tested whether availability of this pivotal cofactor, DMB or its intermediate α-ribazole affect growth and composition of prokaryotic microbial communities. Here we show that in the subtropical, equatorial and polar frontal Pacific Ocean supply of B12 and α-ribazole enhances heterotrophic prokaryotic production and alters the composition of prokaryotic and heterotrophic protist communities. In the polar frontal Pacific, the SAR11 clade and Oceanospirillales increased their relative abundances upon B12 supply. In the subtropical Pacific, Oceanospirillales increased their relative abundance upon B12 supply as well but also downregulated the transcription of the btuB gene, encoding the outer membrane permease for B12. Surprisingly, Prochlorococcus, known to produce pseudo-B12 and not B12, exhibited significant upregulation of genes encoding key proteins of photosystem I + II, carbon fixation and nitrate reduction upon B12 supply in the subtropical Pacific. These findings show that availability of B12 and α-ribazole affect growth and composition of prokaryotic and protist communities in oceanic systems thus revealing far-reaching consequences of methionine biosynthesis and other B12-dependent enzymatic reactions on a community level.

Toward the use of protists as bioindicators of multiple stresses in agricultural soils: A case study in vineyard ecosystems

Management of agricultural soil quality requires fast and cost-efficient methods to identify multiple stressors that can affect soil organisms and associated ecological processes. Here, we propose to use soil protists which have a great yet poorly explored potential for bioindication. They are ubiquitous, highly diverse, and respond to various stresses to agricultural soils caused by frequent management or environmental changes.We test an approach that combines metabarcoding data and machine learning algorithms to identify potential stressors of soil protist community composition and diversity. We measured 17 key variables that reflect various potential stresses on soil protists across 132 plots in 28 Swiss vineyards over 2 years. We identified the taxa showing strong responses to the selected soil variables (potential bioindicator taxa) and tested for their predictive power.Changes in protist taxa occurrence and, to a lesser extent, diversity metrics exhibited great predictive power for the considered soil variables. Soil copper concentration, moisture, pH, and basal respiration were the best predicted soil variables, suggesting that protists are particularly responsive to stresses caused by these variables. The most responsive taxa were found within the clades Rhizaria and Alveolata. Our results also reveal that a majority of the potential bioindicators identified in this study can be used across years, in different regions and across different grape varieties.Altogether, soil protist metabarcoding data combined with machine learning can help identifying specific abiotic stresses on microbial communities caused by agricultural management. Such an approach provides complementary information to existing soil monitoring tools that can help manage the impact of agricultural practices on soil biodiversity and quality.

Contamination with multiple heavy metals decreases microbial diversity and favors generalists as the keystones in microbial occurrence networks

Soil contamination with multiple heavy metals poses threats to human health and ecosystem functioning. Using the Nemerow pollution index, which considers the effects of multiple heavy metals, we compared the diversity and composition of bacteria, fungi and protists and their potential interactions in response to a multi-metal contamination gradient. Multi-metal contamination significantly altered the community composition of bacteria, fungi and protists, and the degree of alteration increased with increasing severity of contamination. The alpha-diversity of bacteria, fungi and protists significantly decreased with increasing contamination level. The dominant generalists, found in all soil samples, were Gammaproteobacteria, Chloroflexi and Bacillus sp, whereas the dominant specialists were Anaerolineaceae, Entoloma sp. and Sandonidae_X sp. The relative abundances of generalists were positively correlated, whereas those of specialists were negatively correlated, with the Nemerow pollution index. In addition, the complexity of the microbial co-occurrence network increased with increasing contamination level. Generalists, rather than specialists, were the keystones in the microbial co-occurrence network and played a crucial role in adaptation to multi-metal contamination through enhanced potential interactions within the entire microbiome. Our results provide insights into the ecological effects of multi-metal contamination on the soil microbiome and will help to develop bio-remediation technologies for contaminated soils.

Biofertilization containing Paenibacillus triticisoli BJ-18 alters the composition and interaction of the protistan community in the wheat rhizosphere under field conditions.

Most studies focus on the effects of biofertilizer on the bacterial and fungal communities, and we still lack an understanding of biofertilizer on the protistan community. Here, the effects of biofertilizer containing Paenibacillus triticisoli BJ-18 on composition and interaction of the protistan community in the wheat rhizosphere were investigated. Biofertilizer application altered soil physicochemical properties and the protistan community composition, and significantly induced an alpha diversity decline. Random forecast and redundancy analysis demonstrated that nitrogenase activity and available phosphorus were the main drivers. Trichomonas classified to the phylum Metamonada was enriched by biofertilizer, and was significantly positive connected with soil nitrogenase activity and some function genes involved in nitrogen-fixation and nitrogen-dissimilation. Biofertilization loosely connected biotic interactions, while it did not affect the stability of the protistan community. Besides, biofertilizer promoted the connections of protists with fungi, bacteria, and archaea. Combined with biotic networks (protists, fungi, bacteria, and archaea) and interactions between protists and soil physicochemical properties/function genes, protists may act as keystone taxa potentially driving soil microbiome composition and function. Overall, these results suggest that the biofertilizer is a driver of the soil protistan community, contributing to ecosystem functioning.

Changes in the Abundance and Taxonomic Composition of Benthic Heterotrophic Protists from Atlantic Sublittoral to Deep-Sea Sediments

Protists are the most diverse eukaryotes on our planet and metabarcoding has revealed an enormous diversity even from deep-sea environments. A range of different species has also been isolated from the deep sea and some have proven able to survive and even grow under deep-sea conditions. However, little is known about how the community structure of benthic protists changes from sublittoral down to abyssal depths. This is especially important regarding island and seamount communities which are surrounded by deep-sea areas potentially isolating them. Using a combination of live-counting and cultivation techniques, we investigated the abundance and taxonomic composition of benthic protist communities in sediments from sublittoral to abyssal depths around three islands and two seamounts of the Azores’ archipelago in the North Atlantic. Protist abundance decreased significantly and community composition changed with increasing depth. While some species were found at all depths, others were only detected in sublittoral or lower bathyal depths, indicating that some benthic taxa are limited in their distribution to a certain depth, whereas others are also present at the deep-sea floor. The proportion of unidentified specimens increased with depths pointing towards a high number of so far undetected species in the deep-sea realm.

Aridity decreases soil protistan network complexity and stability

Protists are ubiquitous and abundant in soil and contribute to key ecosystem processes including nutrient cycling and top-down regulation of soil microbiome. Drought stress will change the protistan community composition and network stability, which introduces uncertainty to predict their functions under a changing climate. A field survey was conducted across >2000 km in contrasting interior land and coastal areas of eastern Australia. We found aridity was the best predictor of protistan community composition, despite significant differences in soil physicochemical and biological properties between the two regions. Aridity may increase the importance of stochasticity in protistan community assembly, while decrease their community-level niche overlaps. More importantly, aridity may reduce the network complexity and stability, based on the difference in network topological features between inland and coastal sites. Altogether, our work provided new insights into the mechanisms through which aridity alters soil protistan communities and highlighted the importance of considering protistan networks when projecting ecological consequences under the climate change scenarios.

Soil properties have more significant effects on the community composition of protists than the rhizosphere effect of rice plants in alkaline paddy field soils

Protists are among the most diverse and major microbial groups in the soil ecosystem and play versatile functional roles for soil fertility and agricultural productivity. However, protist community composition is poorly understood in paddy field soil, especially in alkaline paddy fields. Here we aimed to characterise protist communities of alkaline paddy field soils with a particular focus on the effects of physicochemical properties of the soils and the rhizosphere effect of rice. We selected several alkaline paddy fields across three regions that differed in their soil physicochemical properties along the Kizilirmak River, Turkey, as a model ecosystem. The soils were incubated under submerged conditions with and without rice plants (Oryza sativa L.) to understand the rhizosphere effect on protist community composition. The protist communities were analysed with a high throughput sequencing method. The results showed that Amoebozoa (29.5%) were the most abundant taxonomic group of protists in the paddy fields, followed by Stramenopiles (23.7%), Rhizaria (19.5%), and Alveolata (12.6%). Among the functional groups, consumers (decomposers and predators) were the most dominant protist group (67.7%), followed by autotrophs (21.0%) and pathogens (microbial/animal parasites and plant pathogens) (9.2%). The soil properties have more significant effects driving the community composition of protists than the rhizosphere effect of rice in the paddy field soils. Among the soil properties, pH, exchangeable Na and Ca, EC, and lime were significantly correlated with the shift in the protist community composition. The rhizosphere effect of rice mainly affected phagotrophs and plant pathogens, especially Pythium sp. A significant negative correlation was observed in the relative abundances between phagotrophic protists and plant pathogens, which indicates that the plant pathogens could be top-down controlled by the phagotrophs.

Protist diversity and community complexity in the rhizosphere of switchgrass are dynamic as plants develop

BackgroundDespite their widespread distribution and ecological importance, protists remain one of the least understood components of the soil and rhizosphere microbiome. Knowledge of the roles that protists play in stimulating organic matter decomposition and shaping microbiome dynamics continues to grow, but there remains a need to understand the extent to which biological and environmental factors mediate protist community assembly and dynamics. We hypothesize that protists communities are filtered by the influence of plants on their rhizosphere biological and physicochemical environment, resulting in patterns of protist diversity and composition that mirror previously observed diversity and successional dynamics in rhizosphere bacterial communities.ResultsWe analyzed protist communities associated with the rhizosphere and bulk soil of switchgrass (SG) plants (Panicum virgatum) at different phenological stages, grown in two marginal soils as part of a large-scale field experiment. Our results reveal that the diversity of protists is lower in rhizosphere than bulk soils, and that temporal variations depend on soil properties but are less pronounced in rhizosphere soil. Patterns of significantly prevalent protists groups in the rhizosphere suggest that most protists play varied ecological roles across plant growth stages and that some plant pathogenic protists and protists with omnivorous diets reoccur over time in the rhizosphere. We found that protist co-occurrence network dynamics are more complex in the rhizosphere compared to bulk soil. A phylogenetic bin-based null model analysis showed that protists’ community assembly in our study sites is mainly controlled by homogenous selection and dispersal limitation, with stronger selection in rhizosphere than bulk soil as SG grew and senesced.ConclusionsWe demonstrate that environmental filtering is a dominant determinant of overall protist community properties and that at the rhizosphere level, plant control on the physical and biological environment is a critical driver of protist community composition and dynamics. Since protists are key contributors to plant nutrient availability and bacterial community composition and abundance, mapping and understanding their patterns in rhizosphere soil is foundational to understanding the ecology of the root-microbe-soil system.5stCu76cmNPcXaeF7W4bD3Video