• Soil bacterial community composition strongly differed along a short elevational gradient. • Soil pH and elevation were significantly correlated with soil bacterial community composition. • Degree scores, betweenness centralities, and composition of network hubs differed among elevations.
The elevational distributions of bacterial communities in natural mountain forests, especially along large elevational gradients, have been studied for many years. However, the distributional patterns that underlie variations in soil bacterial communities along small-scale elevational gradients in urban ecosystems are not yet well understood. Using Illumina MiSeq DNA sequencing, we surveyed soil bacterial communities at three elevations on Zijin Mountain in Nanjing City: the hilltop (300 m a.s.l.), the hillside (150 m a.s.l.), and the foot of the hill (0 m a.s.l.). The results showed that edaphic properties differed significantly with elevation. Bacterial community composition, rather than alpha diversity, strongly differed among the three elevations (Adonis: R2 = 0.12, P<0.01). Adonis and DistLM analyses demonstrated that bacterial community composition was highly correlated with soil pH, elevation, total nitrogen (TN), and dissolved organic carbon (DOC). The degree scores, betweenness centralities, and composition of keystone species were distinct among the elevations. These results demonstrate strong elevational partitioning in the distributions of soil bacterial communities along the gradient on Zijin Mountain. Soil pH and elevation together drove the small-scale elevational distribution of soil bacterial communities. This study broadens our understanding of distribution patterns and biotic co-occurrence associations of soil bacterial communities from large elevational gradients to short elevational gradients.
• The riverbed-oxbow lake bed-floodplain-terrace continuum. • Dominant bacteria substantially differed along the continuum. • The highest bacterial diversity in floodplains and the lowest in terraces. • Soil particle and moisture-related factors determine bacterial communities.
Continuous landscape components along the lateral riverside are affected by both hydrologic connectivity and disconnectivity. In recent years, anthropogenic activities and climate changes have caused wetland shrinkage and land degradation along the lateral riverside of many arid and semiarid regions. Since microorganisms are major drivers of soil biochemical cycling, it is essential to examine soil microbial communities along the lateral landscape continuum to understand their ecosystem functioning and predict future land changes. Here, we collected samples along a lateral riverbed center-riverbed edge-oxbow lake-floodplain-terrace continuum in the Xilin River Basin, Inner Mongolia, China. The floodplain had the highest microbial diversity and heterogeneity, with Bacteroidetes, β- and ©-Proteobacteria being the most abundant taxa. In contrast, the terrace had the lowest microbial diversity and heterogeneity, with Acidobacteria, Actinobacteria, Verrucomicrobia, Gemmatimonadetes, and α-Proteobacteria as the most abundant taxa. Silt particle, salinity, and moisture were the most influential factors for bacterial communities along the riverside continuum. Altogether, we demonstrate that dominant bacterial lineages, soil particles, and moisture-related factors are valuable indicators of this continuum, which can be leveraged for early prediction of drought-induced wetland shrinkage and grassland desertification.
• Relative abundances of microbial communities were most related to aggregate proportions in clay-layer soils. • Aggregate content with<0.053 mm in clay-layer soil significantly influence the diversity of soil microbial community. • Complexity of microbial interactions raised along increasing precipitation across sampling sites. • Competition for substrates induced niche differentiation in deeper soils.
Soil microorganisms play a key role in the function of soil ecosystem, yet our knowledge about how microbial communities respond to the typically sandy soil environmental properties along the soil profile is still insufficient. We investigated the soil microbial community patterns from top (0 – 20 cm) to clay-layer (>80 cm) of the typical sandy soils in three regions in China with different levels of precipitation, including Lishu County in Jilin Province (LS), Langfang City in Hebei Province (LF) and Zhengzhou City in Henan Province (ZZ). Our findings showed that small-size aggregates (<0.5 mm) rather than large ones (>= 0.5 mm) dominated the soil profile. The relative abundances of Actinobacteria, Crenarchaeota and Firmicutes were highly related to aggregate proportions of the deep clay-layer soil. The network analysis revealed the distinct community patterns among modules, evidencing niche differentiation along the soil profile. The keystone species OTU_11292 was observed having migrated clearly into the other module of the clay-layer soil. Different roles of the OTU_30 (belonging to Gemmatimonadetes) in soil processes might partly explain the different microbial distribution between top- and clay-layer soils. These findings provided new insights into the candidate mechanisms of microbial diversity maintenance and community patterning of sandy soils, which were necessary for better understanding of ecological rules guiding long-term agricultural practice.
• Biocrust succession alters diazotrophic diversity and community compositions. • Deterministic processes govern diazotrophic community assemblages. • The TOC/TN ratio is a key factor driving diazotrophic community succession. • Diazotrophic networks become less complex with biocrust succession.
The diazotrophic community in biological soil crusts (biocrusts) is the key supplier of nitrogen in dryland. To date, there is still limited information on how biocrust development influences the succession of diazotrophic community, and what are the most important factors mediating diazotrophic communities during biocrust succession. Using the high throughput nifH amplicon sequencing, the diazotrophs in soils at different developmental stages of biocrust were comparatively studied. The results evidenced the decrease of TOC/TN ratio and pH value with biocrust development. Nostoc and Scytonema were the most dominant diazotrophic genera at all biocrust stages, while Azospirillum and Bradyrhizobium were abundant only in bare soil. Diazotrophic co-occurrence networks tended to be less complex and less connected with biocrust succession. The soil TOC/TN ratio was the most dominant factor mediating diazotrophic diversity, community composition and assembly processes, while diazotrophic-diversity and NO3−-N/NH4+-N ratio were positively correlated with the nitrogenase activity during biocrust succession. This study provided novel understandings of nitrogen fixation and succession patterns of diazotrophic community, by showing the effects of biocrust succession on diazotrophic diversity, community composition, community assembly and co-occurrence networks, and recognizing TOC/TN ratio as the most dominant factor mediating diazotrophs during biocrust succession.
• Soil phosphorus shaped both abundant and rare bacterial communities. • Both abundant and rare bacteria exhibited different assembly strategies with successional reforestation. • Deterministic processes increased with succession reforestation.
Uncovering the mechanisms underlying the diversity patterns of abundant and rare species is crucial for terrestrial biodiversity maintenance. However, the response of abundant and rare community assembly to ecological succession has not been explored, particularly considering soil profiles. Here 300 soil samples were collected from reforestation ecosystems from depths of up to 300 cm and horizontal distances of 30-90 cm from a tree. We revealed that soil phosphorus not only affected alpha diversity and community structure, but also mediated the balance of stochastic and deterministic processes for abundant and rare sub-communities, which exhibited contrasting assembly strategies. The abundant sub-community changed from variable selection to stochasticity with the increase of phosphorus, while the rare sub-community shifted from homogeneous selection to stochasticity. Dispersal limitation was the main assembly process in the abundant sub-community, while the rare sub-community was governed primarily by homogeneous selection. Moreover, the relative influence of deterministic processes increased with succession for both sub-communities. At the scale of a single tree, stochastic processes increased with soil depth in rare sub-community, while deterministic processes increased with the radius from a single tree in the abundant sub-community. Overall, our results highlight the importance of the soil phosphorus-driven assembly process in understanding the re-assembly and maintenance of soil bacterial diversity.
• 10-year of CC was a cut-off point in separating soil bacterial community structures. • soil pH and P were well associated with changes of diversity and community structures. • N fixation bacteria were increased with successive year, but P, K solubilizing bacteria decreased. • Monocropped alfalfa simplified the complexity of the cooccurrence networks.
Soil-borne plant diseases cause major economic losses globally. This is partly because their epidemiology is difficult to predict in agricultural fields, where multiple environmental factors could determine disease outcomes. Here we used a combination of field sampling and direct experimentation to identify key abiotic and biotic soil properties that can predict the occurrence of bacterial wilt caused by pathogenic Ralstonia solanacearum. By analyzing 139 tomato rhizosphere soils samples isolated from six provinces in China, we first show a clear link between soil properties, pathogen density and plant health. Specifically, disease outcomes were positively associated with soil moisture, bacterial abundance and bacterial community composition. Based on soil properties alone, random forest machine learning algorithm could predict disease outcomes correctly in 75% of cases with soil moisture being the most significant predictor. The importance of soil moisture was validated causally in a controlled greenhouse experiment, where the highest disease incidence was observed at 60% of maximum water holding capacity. Together, our results show that local soil properties can predict disease occurrence across a wider agricultural landscape, and that management of soil moisture could potentially offer a straightforward method for reducing crop losses to R. solanacearum
• A novel microcosm for identifying phytate-degrading soil microbes is introduced • Phytate microcosms recruited different microbial profiles when compared to controls • Microbial populations recruited by phytate showed phosphatase activity in vitro • Streptomyces were indicated as inherently competitive in solum utilizers of phytate
Fertilizer phosphorus (P) is a finite resource, necessitating the development of innovative solutions for P fertilizer efficiency in agricultural systems. Myo-inositol hexakisphosphate (phytate) constitutes the majority of identified organic P in many soil types and is poorly available to plants. Incorporating phytase-producing biofertilizers into soil presents a viable and environmentally acceptable way of utilizing P from phytate, while reducing the need for mineral P application. A deeper understanding of the microbial ecology in relation to degradation of phytate under natural soil conditions is however needed to obtain successful biofertilizer candidates able to compete in complex soil environments. Here we present the development of a microcosm for studying microbial communities able to colonize and utilize Ca-phytate hotspots in solum. Our results provide evidence that the recruited microbial population mineralizes Ca-phytate. Furthermore, quantification of bacterial genes associated with organic P cycling in alkaline soils indicated that the phosphatases PhoX and PhoD may play a larger role in phytate mineralization in soil than previously recognized. Amplicon sequencing and BioLog® catabolism studies show that hotspots containing Ca-phytate, recruited a different set of microorganisms when compared to those containing an addition of C source alone, with the genus Streptomyces specifically enriched. We propose that Streptomyces represents an hitherto unexplored resource as P biofertilizer with competitive advantage for utilizing CaPhy in an inherently competitive soil environment. We further conclude that the use of our newly designed microcosm presents an innovative approach for isolating soil microorganisms with the potential to degrade precipitated phytate in solum.
• We measured soil variables along the profile in two alpine ecosystems. • Most of soil properties decreased with depth and varied with time. • Root and microbial biomass decreased with depth and increased with time. • Soil enzyme activities decreased with depth but showed little change with time. • Soil properties and microbial biomass were more dynamic than enzyme activities.
Microbial biomass and extracellular enzyme activities control the rate of soil organic carbon decomposition, thereby affecting soil carbon pool. However, seasonal dynamics of soil microbial properties at different depths of the soil profile remain unclear. In this study, we sampled soils in the early, middle and late growing season at different soil depths (0–100 cm) in two alpine ecosystems (meadow and shrubland) on the Tibetan Plateau. We measured plant belowground biomass, soil properties, microbial biomass and extracellular enzyme activities. We found that soil properties changed significantly with sampling time and soil depth. Specifically, most of soil properties consistently decreased with increasing soil depth, but inconsistently varied with sampling time. Moreover, root biomass and microbial biomass decreased with increasing soil depth and increased with sampling time during the growing season. However, microbial extracellular enzyme activities and their vector properties all changed with depth, but did not vary significantly with time. Taken together, these results show that soil properties, microbial biomass and extracellular enzyme activities mostly decline with increasing depth of the soil profile, and soil properties and microbial biomass are generally more variable during the growing season than extracellular enzyme activities across the soil profile in these alpine ecosystems. Further studies are needed to investigate the changes in soil microbial community composition and function at different soil depths over the growing season, which can enhance our mechanistic understanding of whole-profile soil carbon dynamics of alpine ecosystems under climate change.
• Straw returning significantly affects silicon fraction transformation; • Straw return affects soil microbial community composition; • Soil microbe interacts with silicon fraction transformation and promote rice yield.
Returning crop straw into the soil is an important practice to balance biogenic and bioavailable silicon (Si) pool in paddy, which is crucial for the healthy growth of rice. However, owing to little knowledge about soil microbial communities responsible for straw degradation, how straw return affects Si bioavailability, its uptake, and rice yield remains elusive. Herein, we investigate the change of soil Si fractions and microbial community in a 39-year-old paddy field amended by a long-term straw return. Results show that rice straw return significantly increased soil bioavailable Si and rice yield from 29.9% to 61.6% and from 14.5% to 23.6%, respectively, when compared to NPK fertilization alone. Straw return significantly altered soil microbial community abundance. Acidobacteria was positively and significantly related to amorphous Si, while Rokubacteria at phylum level, Deltaproteobacteria, and Holophagae at class level was negatively and significantly related to organic matter adsorbed and Fe/Mn-oxide-combined Si in soils. Redundancy analysis of their correlations further demonstrated that Si status significantly explained 12% of soil bacterial community variation. These findings suggest that soil bacteria community and diversity interact with Si mobility by altering its transformation, thus resulting in the balance of various nutrient sources to drive biological Si cycle in agroecosystem.
