Spatial distribution patterns across multiple microbial taxonomic groups.

Even in the vertical dimension, soil bacterial communities are spatially distributed in a distance-decay relationship (DDR). However, whether this pattern is universal among all soil microbial taxonomic groups, and how body size influences this distribution, remains elusive. Our study consisted of obtaining 140 soil samples from two adjacent ecosystems in the Yellow River Delta (YRD), both nontidal and tidal, and measuring the DDR between topsoil and subsoil for bacteria, archaea, fungi and protists (rhizaria). Our results showed that the entire community generally fitted the DDR patterns (P < 0.001), this was also true at the kingdom level (P < 0.001, with the exception of the fungal community), and for most individual phyla (47/75) in both ecosystems and with soil depth. Meanwhile, these results presented a general trend that the community turnover rate of nontidal soils was higher than tidal soils (P < 0.05), and that the rate of topsoil was also higher than that of subsoil (P < 0.05). Additionally, microbial spatial turnover rates displayed a negative relationship with body sizes in nontidal topsoil (R2 = 0.29, P = 0.009), suggesting that the smaller the body size of microorganisms, the stronger the spatial limitation was in this environment. However, in tidal soils, the body size effect was negligible, probably owing to the water's fluidity. Moreover, community assembly was judged to be deterministic, and heterogeneous selection played a dominant role in the different environments. Specifically, the spatial distance was much more influential, while the soil salinity in these ecosystems was the major environmental factor in selecting the distributions of microbial communities. Overall, this study revealed that microbial community compositions at different taxonomic levels followed relatively consistent distribution patterns and mechanisms in this coastal area.

The Stability of Phyto-Zooplanktonic Networks Varied with Zooplanktonic Sizes in Chinese Coastal Ecosystem.

The linkages between phytoplankton and zooplankton are crucial for the stability of complex food webs and the flow of energy within the marine ecosystem. Despite body size exhibiting multiple effects on the planktonic community assembly and the dispersal scale, its role in determining the stability of phyto-zooplanktonic co-occurrence patterns remains unclear. Here, we focused on more than 13,000 kilometers of the Chinese coast to study the diatom-dominated plankton ecosystem and to report the significant negative effects of zooplanktonic body sizes on the topological properties of phyto-zooplanktonic networks (PZNs) by using more than 500 species from 251 samples taken along the coastline. PZNs tended to be more complex and stable when phytoplankton associated with smaller zooplankton. Particularly, the subnetworks of dominant phytoplankton displayed differences with different zooplanktonic body sizes. The zooplankton with larger and smaller body sizes tended to interact with dinoflagellates and diatoms, respectively. Additionally, abiotic factors (i.e., water temperature, pH, salinity, and metal concentrations) displayed significant effects on PZNs via the shifting of zooplanktonic composition, and the zooplanktonic body sizes altered the network modules' associations with different environmental factors. Our study elucidated the general relationship between zooplanktonic body sizes and the stability of PZNs, which provides new insights into marine food webs. IMPORTANCE Body size is a key life trait of aquatic plankton that affects organisms' metabolic rates and ecological functions; however, its specific effects on interactions between phytoplankton and zooplankton are poorly understood. We collected planktonic species and their body size data along more than 13,000 kilometers of coastline to explore the role of zooplanktonic body size in maintaining the stability of phyto-zooplanktonic networks (PZNs). We found that zooplankton play a more important role in maintaining PZN stability than do phytoplankton as well as that the PZN would be more complex and stable with smaller zooplankton. Furthermore, this work revealed that body size significantly determined the relationships between environmental factors and network structure. Overall, these findings lay a general relationship between zooplanktonic body sizes and the stability of PZNs, which helps us further explore the micro food web of coastal ecosystems.

Soil microbial community assembly and stability are associated with potato (Solanum tuberosum L.) fitness under continuous cropping regime.

Continuous cropping obstacles caused by the over-cultivation of a single crop trigger soil degradation, yield reduction and the occurrence of plant disease. However, the relationships among stability, complexity and the assembly process of soil microbial community with continuous cropping obstacles remains unclear. In this study, molecular ecological networks analysis (MENs) and inter-domain ecological networks analysis (IDENs), and a new index named cohesion tools were used to calculate the stability and complexity of soil microbial communities from eight potato cultivars grown under a continuous cropping regime by using the high-throughput sequencing data. The results showed that the stability (i.e., robustness index) of the bacterial and fungal communities for cultivar ZS5 was significantly higher, and that the complexity (i.e., cohesion values) was also significantly higher in the bacterial, fungal and inter-domain communities (i.e., bacterial-fungal community) of cultivar ZS5 than other cultivars. Network analysis also revealed that Actinobacteria and Ascomycota were the dominant phyla within intra-domain networks of continuous cropping potato soil communities, while the phyla Proteobacteria and Ascomycota dominated the correlation of the bacterial-fungal network. Infer community assembly mechanism by phylogenetic-bin-based null model analysis (iCAMP) tools were used to calculate the soil bacterial and fungal communities' assembly processes of the eight potato cultivars under continuous cropping regime, and the results showed that the bacterial community was mainly dominated by deterministic processes (64.19% - 81.31%) while the fungal community was mainly dominated by stochastic processes (78.28% - 98.99%), indicating that the continuous-cropping regime mainly influenced the potato soil bacterial community assembly process. Moreover, cultivar ZS5 possessed a relatively lower homogeneous selection, and a higher TP, TN, AP and yield than other cultivars. Our results indicated that the soil microbial network stability and complexity, and community assemble might be associated with yield and soil properties, which would be helpful in the study for resistance to potato continuous cropping obstacles.

ddPCR surpasses classical qPCR technology in quantitating bacteria and fungi in the environment.

Quantitative real-time PCR (qPCR) has been widely used in quantifying bacterial and fungal populations in various ecosystems, as well as the fungi to bacteria ratio (F:B ratio). Recently, researchers have begun to apply droplet digital PCR (ddPCR) to this area; however, no study has systematically compared qPCR and ddPCR for quantitating both bacteria and fungi in environmental samples at the same time. Here, we designed probe-primer pair combinations targeting the 16S rRNA gene and internal transcribed spacer (ITS) for the detection of bacteria and fungi, respectively, and tested both SYBR Green and TaqMan approaches in qPCR and ddPCR methods for mock communities and in real environmental samples. In mock communities, the quantification results of ddPCR were significantly closer to expected values (p < .05), and had smaller coefficients of variations (p < .05) than qPCR, suggesting ddPCR was more accurate and repeatable. In environmental samples, ddPCR consistently quantified ITS and 16S rRNA gene concentrations in all four habitats without abnormal overestimation or underestimation, and the F:B ratio obtained by ddPCR was consistent with phospholipid fatty acid analysis. Our results indicated that ddPCR had better precision, repeatability, sensitivity, and stability in bacterial and fungal quantitation than qPCR. Although ddPCR has high cost, complicated processes and restricted detection range, it shows insensitivity to PCR inhibitors and the potential of quantifying long target fragments. We expect that ddPCR, which is complementary to qPCR, will contribute to microbial quantification in environmental monitoring and evaluation.

Fungal dynamics and potential functions during anaerobic digestion of food waste.

Fungi could play an important role during anaerobic digestion (AD), but have received less attention than prokaryotes. Here, AD bioreactors of food waste were performed to explore fungal succession and their potential ecological and engineering value. We found that similar patterns in fungal biomass and diversity, decreasing from the initial time point (Day 0) to the lowest value within 3-6 days and then started to rise and stabilized between 9 and 42 days. Throughout the entire AD process, variations in fungal community composition were observed and dominant fungal taxa have the potential ability to degrade complex organic matter and alleviate fatty acid and ammonia accumulation. Furthermore, we found that deterministic processes gradually dominated fungal assembly succession (up to 84.85% at the final stage), suggesting changing environmental status responsible for fungal community dynamics and specifically, fungal community structure, diversity and biomass were regulated by different environmental variables or the same variables with opposite effects. AD bioreactors could directionally select specific fungal taxa over time, but some highly abundant fungi could not be mapped to any fungal species with defined function in the reference database, so function prediction relying on PICRUSt2 may underestimate fungal function in AD systems. Collectively, our study confirmed fungi have important ecological and engineering values in AD systems.

The large-scale spatial patterns of ecological networks between phytoplankton and zooplankton in coastal marine ecosystems.

Although autotrophic phytoplankton and heterotrophic zooplankton both play important roles in the food web of marine ecosystem, their comprehensive interactions and spatial patterns at continental scale remain poorly studied. Here, we collected 251 seawater samples along 13,000 km of Chinese coastline, and microscopically investigated the latitudinal gradients of planktonic diversities. In total, 307 phytoplanktonic and 311 zooplanktonic species were visually identified. Using the newly developed Inter-Domain Ecological Networks (IDENs) approach, the phytoplankton-zooplankton interaction networks were constructed. We found that the phyto-zooplankton network structure was varied across three regions, more complex and numerous connections along the southern coast than in the north. In addition, some particular associations between zooplanktonic and phytoplanktonic groups were found to be localized in specific regions. Furthermore, the seawater temperature and salinity were the major driving force for shaping planktonic interaction networks. These results provide a deeper understanding of planktonic biogeography and phytoplankton-zooplankton interaction patterns.

Fungi and cercozoa regulate methane-associated prokaryotes in wetland methane emissions.

Wetlands are natural sources of methane (CH4) emissions, providing the largest contribution to the atmospheric CH4 pool. Changes in the ecohydrological environment of coastal salt marshes, especially the surface inundation level, cause instability in the CH4 emission levels of coastal ecosystems. Although soil methane-associated microorganisms play key roles in both CH4 generation and metabolism, how other microorganisms regulate methane emission and their responses to inundation has not been investigated. Here, we studied the responses of prokaryotic, fungal and cercozoan communities following 5 years of inundation treatments in a wetland experimental site, and molecular ecological networks analysis (MENs) was constructed to characterize the interdomain relationship. The result showed that the degree of inundation significantly altered the CH4 emissions, and the abundance of the pmoA gene for methanotrophs shifted more significantly than the mcrA gene for methanogens, and they both showed significant positive correlations to methane flux. Additionally, we found inundation significantly altered the diversity of the prokaryotic and fungal communities, as well as the composition of key species in interactions within prokaryotic, fungal, and cercozoan communities. Mantel tests indicated that the structure of the three communities showed significant correlations to methane emissions (p < 0.05), suggesting that all three microbial communities directly or indirectly contributed to the methane emissions of this ecosystem. Correspondingly, the interdomain networks among microbial communities revealed that methane-associated prokaryotic and cercozoan OTUs were all keystone taxa. Methane-associated OTUs were more likely to interact in pairs and correlated negatively with the fungal and cercozoan communities. In addition, the modules significantly positively correlated with methane flux were affected by environmental stress (i.e., pH) and soil nutrients (i.e., total nitrogen, total phosphorus and organic matter), suggesting that these factors tend to positively regulate methane flux by regulating microbial relationships under inundation. Our findings demonstrated that the inundation altered microbial communities in coastal wetlands, and the fungal and cercozoan communities played vital roles in regulating methane emission through microbial interactions with the methane-associated community.

Warming reshaped the microbial hierarchical interactions.

Global warming may alter microbially mediated ecosystem functions through reshaping of microbial diversity and modified microbial interactions. Here, we examined the effects of 5-year experimental warming on different microbial hierarchical groups in a coastal nontidal soil ecosystem, including prokaryotes (i.e., bacteria and archaea), fungi, and Cercozoa, which is a widespread phylum of protists. Warming significantly altered the diversity and structure of prokaryotic and fungal communities in soil and additionally decreased the complexity of the prokaryotic network and fragmented the cercozoan network. By using the Inter-Domain Ecological Network approach, the cross-trophic interactions among prokaryotes, fungi, and Cercozoa were further investigated. Under warming, cercozoan-prokaryotic and fungal-prokaryotic bipartite networks were simplified, whereas the cercozoan-fungal network became slightly more complex. Despite simplification of the fungal-prokaryotic network, the strengthened synergistic interactions between saprotrophic fungi and certain prokaryotic groups, such as the Bacteroidetes, retained these phyla within the network under warming. In addition, the interactions within the fungal community were quite stable under warming conditions, which stabilized the interactions between fungi and prokaryotes or protists. Additionally, we found the microbial hierarchical interactions were affected by environmental stress (i.e., salinity and pH) and soil nutrients. Interestingly, the relevant microbial groups could respond to different soil properties under ambient conditions, whereas under warming these two groups tended to respond to similar soil properties, suggesting network hub species responded to certain environmental changes related to warming, and then transferred this response to their partners through trophic interactions. Finally, warming strengthened the network modules' negative association with soil organic matters through some fungal hub species, which might trigger soil carbon loss in this ecosystem. Our study provides new insights into the response and feedback of microbial hierarchical interactions under warming scenario.

Meadow degradation increases spatial turnover rates of the fungal community through both niche selection and dispersal limitation.

The alpine meadow ecosystem, as the main ecosystem of the Qinghai-Tibet Plateau, has been heavily degraded over the past several decades due to overgrazing and climate change. Although soil microorganisms play key roles in the stability and succession of grassland ecosystems, their response to grassland degradation has not been investigated at spatial scale. Here, we systematically analyzed the spatial turnover rates of soil prokaryotic and fungal communities in degraded and undegraded meadows through distance-decay relationship (DDR) and species area relationship (SAR), as well as the community assembly mechanisms behind them. Although the composition and structure of both fungal and prokaryotic communities showed significant changes between undegraded and degraded meadows, steeper spatial turnover rates were only observed in fungi (Degraded Alpine Meadow ß = 0.0142, Undegraded Alpine Meadow ß = 0.0077, P < 0.05). Mantel tests indicated that edaphic variables and vegetation factors showed significant correlations to the ß diversity of fungal community only in degraded meadow, suggesting soil and vegetation heterogeneity both contributed to the variation of fungal community in that system. Correspondingly, a novel phylogenetic null model analysis demonstrated that environmental selection was enhanced in the fungal community assembly process during meadow degradation. Interestingly, dispersal limitation was also enhanced for the fungal community in the degraded meadow, and its relative contribution to other assembly process (i.e. selection and drift) showed a significant linear increase with spatial distance, suggesting that dispersal limitation played a greater role as distance increased. Our findings indicated the spatial scaling of the fungal community is altered during meadow degradation by both niche selection and dispersal limitation. This study provides a new perspective for the assessment of soil microbial responses to vegetation changes in alpine areas.

Sampling cores and sequencing depths affected the measurement of microbial diversity in soil quadrats.

Due to the massive quantity and broad phylogeny, an accurate measurement of microbial diversity is highly challenging in soil ecosystems. Initially, the deviation caused by sampling should be adequately considered. Here, we attempted to uncover the effect of different sampling strategies on α diversity measurement of soil prokaryotes. Four 1 m2 sampling quadrats in a typical grassland were thoroughly surveyed through deep 16S rRNA gene sequencing (over 11 million reads per quadrat) with numerous replicates (33 soil sampling cores with total 141 replicates per quadrat). We found the difference in diversity was relatively small when pooling soil cores before and after DNA extraction and sequencing, but they were both superior to a non-pooling strategy. Pooling a small number of soil cores (i.e., 5 or 9) combined with several technical replicates is sufficient to estimate diversities for soil prokaryotes, and there is great flexibility in pooling original samples or data at different experimental steps. Additionally, the distribution of local α diversity varies with sampling core number, sequencing depth, and abundance distribution of the community, especially for high orders of Hill diversity index (i.e., Shannon entropy and inverse Simpson index). For each grassland soil quadrat (1 m2), retaining 100,000 reads after taxonomic clustering might be a realistic option, as these number of reads can efficiently cover the majority of common species in this area. Our findings provide important guidance for soil sampling strategy, and the general results can serve as a basis for further studies.

Unraveling Mechanisms and Impact of Microbial Recruitment on Oilseed Rape (Brassica napus L.) and the Rhizosphere Mediated by Plant Growth-Promoting Rhizobacteria.

Plant growth-promoting rhizobacteria (PGPR) are noticeably applied to enhance plant nutrient acquisition and improve plant growth and health. However, limited information is available on the compositional dynamics of rhizobacteria communities with PGPR inoculation. In this study, we investigated the effects of three PGPR strains, Stenotrophomonas rhizophila, Rhodobacter sphaeroides, and Bacillus amyloliquefaciens on the ecophysiological properties of Oilseed rape (Brassica napus L.), rhizosphere, and bulk soil; moreover, we assessed rhizobacterial community composition using high-throughput Illumina sequencing of 16S rRNA genes. Inoculation with S. rhizophila, R. sphaeroides, and B. amyloliquefaciens, significantly increased the plant total N (TN) (p < 0.01) content. R. sphaeroides and B. amyloliquefaciens selectively enhanced the growth of Pseudomonadacea and Flavobacteriaceae, whereas S. rhizophila could recruit diazotrophic rhizobacteria, members of Cyanobacteria and Actinobacteria, whose abundance was positively correlated with inoculation, and improved the transformation of organic nitrogen into inorganic nitrogen through the promotion of ammonification. Initial colonization by PGPR in the rhizosphere affected the rhizobacterial community composition throughout the plant life cycle. Network analysis indicated that PGPR had species-dependent effects on niche competition in the rhizosphere. These results provide a better understanding of PGPR-plant-rhizobacteria interactions, which is necessary to develop the application of PGPR.

The Succession of Bacterial Community Attached on Biodegradable Plastic Mulches During the Degradation in Soil.

Despite the increasing application of biodegradable plastic mulches (BDMs) in agriculture, the colonization and succession of the attached microbial community on BDMs during their degradation processes remain poorly characterized. Here, we buried four types of commonly used BDMs, including pure polylactic acid (PLA), pure polybutylene adipate terephthalate (PBAT), and two mixtures of PLA and PBAT (85:15 and 15:85 w/w), and one classic polyethylene (PE) mulch in soil for 5 months. Both plastic components and incubation time significantly shaped the ß-diversities of microbiota on the plastic mulches (p < 0.001). Meanwhile, the microbial compositions and community structures on BDMs were significantly different from PE mulch, and when excluding PE mulch, the microbiota varied more with time than by the composition of the four BDMs. The orders Burkholderiales and Pseudonocardiales were dominant on most BDMs across different time points. The genus Ramlibacter was revealed as a common biomarker for both PLA and PBAT by random-forest model, and all biomarkers for the BDMs belonged to the dominant order Burkholderiales. In addition, degradation-related and pathogen-related functional taxa were enriched in all mulches among all 40 functional groups, while surprisingly, potential pathogens were detected at higher levels on BDMs than PE. For community assembly on all mulches, the drift and dispersal processes played more important roles than selection, and in particular, the contribution of stochastic drift increased during the degradation process of BDMs while selection decreased, while the opposite trend was observed with PE mulch. Overall, our results demonstrated some degradation species and pathogens were specifically enriched on BDMs, though stochastic processes also had important impacts on the community assembly. It suggested that, similar to conventional plastic mulch, the increased usage of BDMs could lead to potential hazards to crops and human health.

Steeper spatial scaling patterns of subsoil microbiota are shaped by deterministic assembly process.

Although many studies have investigated the spatial scaling of microbial communities living in surface soils, very little is known about the patterns within deeper strata, nor is the mechanism behind them. Here, we systematically assessed spatial scaling of prokaryotic biodiversity within three different strata (Upper: 0-20 cm, Middle: 20-40 cm, and Substratum: 40-100 cm) in a typical grassland by examining both distance-decay (DDRs) and species-area relationships (SARs), taxonomically and phylogenetically, as well as community assembly processes. Each layer exhibited significant biogeographic patterns in both DDR and SAR (p < .05), with taxonomic turnover rates higher than phylogenetic ones. Specifically, the spatial turnover rates, ß and z values, respectively, ranged from 0.016 ± 0.005 to 0.023 ± 0.005 and 0.065 ± 0.002 to 0.077 ± 0.004 across soil strata, and both increased with depth. Moreover, the prokaryotic community in grassland soils assembled mainly according to deterministic rather than stochastic mechanisms. By using normalized stochasticity ratio (NST) based on null model, the relative importance of deterministic ratios increased from 48.0 to 63.3% from Upper to Substratum, meanwhile a phylogenetic based method revealed average ßNTI also increased with depth, from -5.29 to 19.5. Using variation partitioning and distance approaches, both geographic distance and soil properties were found to strongly affect biodiversity structure, the proportions increasing with depth, but spatial distance was always the main underlying factor. These indicated increasingly deterministic proportions in accelerating turnover rates for spatial assembly of prokaryotic biodiversity. Our study provided new insights on biogeography in different strata, revealing importance of assembly patterns and mechanisms of prokaryote communities in below-surface soils.