Primary Succession Research Articles

Diverse rhizosphere-associated Pseudomonas genomes from along a Wadden Island salt marsh transition zone

Soil microbes are key drivers of ecosystem processes promoting nutrient cycling, system productivity, and resilience. While much is known about the roles of microbes in established systems, their impact on soil development and the successional transformation over time remains poorly understood. Here, we provide 67 diverse, rhizosphere-associated Pseudomonas draft genomes from an undisturbed salt march primary succession spanning >100 years of soil development. Pseudomonas are cosmopolitan bacteria with a significant role in plant establishment and growth. We obtained isolates associated with Limonium vulgare and Artemisia maritima, two typical salt marsh perennial plants with roles in soil stabilization, salinity regulation, and biodiversity support. We anticipate that our data, in combination with the provided physiochemical measurements, will help identify genomic signatures associated with the different selective regimes along the successional stages, such as varying soil complexity, texture, and nutrient availability. Such findings would advance our understanding of Pseudomonas’ role in natural soil ecosystems and provide the basis for a better understanding of the roles of microbes throughout ecosystem transformations.

Distinct contributions of microbial and plant residues to SOC during ecosystem primary succession in a Tibetan glacier foreland

Soil organic carbon (SOC) rapidly accumulates during ecosystem primary succession in glacier foreland. This makes it an ideal model for studying soil carbon sequestration and stabilization, which are urgently needed to mitigate climate change. Here, we investigated SOC dynamics in the Kuoqionggangri glacier foreland on the Tibetan Plateau. The study area along a deglaciation chronosequence of 170-year comprising three ecosystem succession stages, including barren ground, herb steppe, and legume steppe. We quantified amino sugars, lignin phenols, and relative expression of genes associated with carbon degradation to assess the contributions of microbial and plant residues to SOC, and used FT-ICR mass spectroscopy to analyze the composition of dissolved organic matter. We found that herbal plant colonization increased SOC by enhancing ecosystem gross primary productivity, while subsequent legumes development decreased SOC, due to increased ecosystem respiration from labile organic carbon inputs. Plant residues were a greater contributor to SOC than microbial residues in the vegetated soils, but they were susceptible to microbial degradation compared to the more persistent and continuously accumulating microbial residues. Our findings revealed the organic carbon accumulation and stabilization process in early soil development, which provides mechanism insights into carbon sequestration during ecosystem restoration under climate change.

Closing the gap: examining the impact of source habitat proximity on plant and soil microbial communities in post-mining spoil heap succession.

Revegetation of barren substrates is often determined by the composition and distance of the nearest plant community, serving as a source of colonizing propagules. Whether such dispersal effect can be observed during the development of soil microbial communities, is not clear. In this study, we aimed to elucidate which factors structure plant and soil bacterial and fungal communities during primary succession on a limestone quarry spoil heap, focusing on the effect of distance to the adjoining xerophilous grassland. We established a grid of 35 plots covering three successional stages - initial barren substrate, early successional community and late successional grassland ecosystem, the latter serving as the primary source of soil colonization. On these plots, we performed vegetation surveys of plant community composition and collected soil cores to analyze soil chemical properties and bacterial and fungal community composition. The composition of early successional plant community was significantly affected by the proximity of the source late successional community, however, the effect weakened when the distance exceeded 20 m. Early successional microbial communities were structured mainly by the local plant community composition and soil chemical properties, with minimal contribution of the source community proximity. These results show that on small spatial scales, species migration is an important determinant of plant community composition during primary succession while the establishment of soil microbial communities is not limited by dispersal and is primarily driven by local biotic and abiotic conditions.

Bacterial Community Structure Modulates Soil Phosphorus Turnover at Early Stages of Primary Succession

AbstractMicrobes are the drivers of soil phosphorus (P) cycling in terrestrial ecosystems; however, the role of soil microbes in mediating P cycling in P‐rich soils during primary succession remains uncertain. This study examined the impacts of bacterial community structure (diversity and composition) and its functional potential (absolute abundances of P‐cycling functional genes) on soil P cycling along a 130‐year glacial chronosequence on the eastern Tibetan Plateau. Bacterial community structure was a better predictor of soil P fractions than P‐cycling genes along the chronosequence. After glacier retreat, the solubilization of inorganic P and the mineralization of organic P were significantly enhanced by increased bacterial diversity, changed interspecific interactions, and abundant species involved in soil P mineralization, thereby increasing P availability. Although 84% of P‐cycling genes were associated with organic P mineralization, these genes were more closely associated with soil organic carbon than with organic P. Bacterial carbon demand probably determined soil P turnover, indicating the dominant role of organic matter decomposition processes in P‐rich alpine soils. Moreover, the significant decrease in the complexity of the bacterial co‐occurrence network and the taxa‐gene‐P network at the later stage indicates a declining dominance of the bacterial community in driving soil P cycling with succession. Our results reveal that bacteria with a complex community structure have a prominent potential for biogeochemical P cycling in P‐rich soils during the early stages of primary succession.

Distinctive patterns of bacterial community succession in the riverine micro-plastisphere in view of biofilm development and ecological niches

Exploring plastic bacterial community succession is a crucial step in analyzing and predicting the ecological assembly processes of the plastisphere and its associated environmental impacts. However, microbial biofilm development and niche differentiation during plastic bacterial community succession have rarely scarcely considered. Here, we assessed the differences between three microplastics (MPs) and two natural polymers in terms of biofilm development and niche properties during bacterial community succession, and identified a genus of MPs-degrading bacteria with strong competitive potential in the plastisphere. MPs biofilm development exhibits secondary succession characteristics, whereas natural polymer biofilms persist during the primary succession stage. During succession in plastic bacterial communities, the relationship between nutrient resources and microbial competition was reflected in a positive correlation between species competition and niche breadth, which contradicted the common belief that increased nutrient availability leads to reduced competition. Furthermore, the co-occurrence network revealed that specialists were species with greater competitive potential within the plastisphere. Additionally, the MPs-degrading Exiguobacterium genus represented a key taxon in the plastisphere. Our study provides a reliable pathway for revealing the specificity of plastic bacterial community succession from multiple perspectives and enhances the understanding of ecological assembly processes in the plastisphere.

Soil Formation on Loamy Deposits in Technogenic Landscapes of the Taiga Zone in the North-Eastern Part of European Russia

The paper highlights the influence of moisture on the soil formation process on loamy deposits during the primary vegetation succession. The study was carried out in the north-eastern part of European Russia (Komi Republic) in the middle taiga subzone. The authors analyzed young soils on the territory of a quarry for extraction of loamy grounds and background soils in the vicinity of it. Planting the Siberian spruce cultures on the territory of the quarry activated formation of the tree layer and thereby accelerated formation of the zonal type soils. The third succession decade in drained conditions saw formation of organic soil horizons (litters), a decrease in soil density in the upper profile part, a tendency to redistribute and differentiate the silty fraction by one-and-a-half oxides, indicating the beginning of selective podzolization. The rise in soil moisture content increased conservation of organic residues (peat formation) and made gley formation active. The quarry soils, like background soils, increased in acidity, carbon and nitrogen reserves along with the soil moisture content increase. In automorphic soil formation conditions, the rate of organic carbon accumulation in the upper 0–20-cm layer is 0.4 t· ha–1·year1; the excessive soil moisture content further increased it (1.0–1.2 t·ha–1·year1). The reserves of Corg in the upper 20-cm soil layer of young soils are by 2–4 times less than those in background soils.

Primary succession of Bifidobacteria drives pathogen resistance in neonatal microbiota assembly

Human microbiota assembly commences at birth, seeded by both maternal and environmental microorganisms. Ecological theory postulates that primary colonizers dictate microbial community assembly outcomes, yet such microbial priority effects in the human gut remain underexplored. Here using longitudinal faecal metagenomics, we characterized neonatal microbiota assembly for a cohort of 1,288 neonates from the UK. We show that the pioneering neonatal gut microbiota can be stratified into one of three distinct community states, each dominated by a single microbial species and influenced by clinical and host factors, such as maternal age, ethnicity and parity. A community state dominated by Enterococcus faecalis displayed stochastic microbiota assembly with persistent high pathogen loads into infancy. In contrast, community states dominated by Bifidobacterium, specifically B. longum and particularly B. breve, exhibited a stable assembly trajectory and long-term pathogen colonization resistance, probably due to strain-specific functional adaptions to a breast milk-rich neonatal diet. Consistent with our human cohort observation, B. breve demonstrated priority effects and conferred pathogen colonization resistance in a germ-free mouse model. Our findings solidify the crucial role of Bifidobacteria as primary colonizers in shaping the microbiota assembly and functions in early life.

Distribution of Woody Biomass on the Outwash Plain of a Retreating Glacier in Southern Iceland: Role of Microhabitat and Substrate

The Skaftafellsjökull is an outlet glacier in southern Iceland that has been retreating since 1890. While multiple studies have examined primary succession on the foreland of this glacier, no study has examined the distribution of woody biomass on the outwash plain. We investigated the distribution of one species, Betula pubescens, that grows on the foreland moraines and outwash plain of this glacier. The topography of the outwash plain is heterogeneous, consisting of broad bars of outwash gravel and boulders that are separated by narrow incised channels and broader swales. Vegetation on the outwash plain is primarily a moss–heath community. Birch are sparse on the outwash bar tops, but are more abundant and larger in the channels and swales between the bars. Although the area of the channels on the outwash plain is much less than that of the bar surfaces, the woody biomass of the outwash plain is dominated by the birch within these channels. Consequently, the mean woody biomass of the outwash plain exceeds that of the moraines. We propose that the microhabitat of the outwash plain channels provides a favorable environment for the growth of birch, primarily by providing a fine-grained substrate that promotes successful seeding and growth.

Plant antagonistic facilitation across environmental gradients: a soil-resource ecosystem engineering model.

Theory questions the persistence of nonreciprocal interactions in which one plant has a positive net effect on a neighbor that, in return, has a negative net impact on its benefactor - a phenomenon known as antagonistic facilitation. We develop a spatially explicit consumer-resource model for belowground plant competition between ecosystem engineers, plants able to mine resources and make them available for any other plant in the community, and exploiters. We use the model to determine in what environmental conditions antagonistic facilitation via soil-resource engineering emerges as an optimal strategy. Antagonistic facilitation emerges in stressful environments where ecosystem engineers' self-benefits from mining resources outweigh the competition with opportunistic neighbors. Among all potential causes of stress considered in the model, the key environmental parameter driving changes in the interaction between plants is the proportion of the resource that becomes readily available for plant consumption in the absence of any mining activity. Our results align with theories of primary succession and the stress gradient hypothesis. However, we find that the total root biomass and its spatial allocation through the root system, often used to measure the sign of the interaction between plants, do not predict facilitation reliably.

Anti-seasonal flooding drives substantial alterations in riparian plant diversity and niche characteristics in a unique hydro-fluctuation zone.

Human-induced disturbances such as dam construction and regulation have led to widespread alterations in hydrological processes and thus substantially influence plant characteristics in the hydro-fluctuation zones (HFZs). To reveal utilization of limited resources and mechanisms of inter-specific competition and species co-existence of plant communities based on niche breadth and overlap under the different HFZs of the Three Gorges Reservoir (TGR) in China, we conducted a field investigation with 368 quadrats on the effects of hydrological alterations on plant diversity and niche characteristics. The results showed anti-seasonal flooding precipitated the gradual disappearance of the original diverse niches, resulting in the reduction of plant species richness and functional diversity and more obvious competition among plant species with similar resource requirements. Annuals, perennials and shrubs accounted for 71.23%, 27.39% and 1.37%, respectively, suggesting that annuals and flood-tolerant riparian herbs were favored under such novel flooding conditions. A consistent increase in species number, Shannon-Wiener diversity index and Simpson dominance index with altitude was inconsistent with hump-shaped diversity-disturbance relationship of the intermediate disturbance hypothesis, while the opposite trend was observed for the Pielou evenness index. This species distribution pattern might be caused by several synergetic attributes (e.g., the submergence depth, plant tolerant capacity to flooding, life form, dispersal mode and inter-specific competition). Vegetation types shifted from xerophytes to mesophytes and eventually to hygrophytes with the increasing flooding time in the HFZs. Hydrological alterations proved to be the paramount driver of vegetation distribution in the different HFZs. The niche analysis provided the first insights on the mechanisms of resource utilization and inter-specific competition, of which annuals could germinate quickly after soil drainage to achieve the greatest competitive advantages and occupy a larger niche space than other plants. Vegetation was still in the early stage of primary succession in the novel riparian forests. Therefore, vegetation restoration strategies should be biased towards herbaceous plants, due to annuals with better environmental adaptability, supplemented by shrubs and small trees. To establish a complete reference system for vegetation restoration, natural vegetation monitory plots in the different succession stages should be established in the different HFZs of the TGR, and their environmental conditions, community structures and inter-specific relationships further analyzed.

Competition in the Periphytic Algal Community during the Colonization Process: Evidence from the World's Largest Water Diversion Project.

Periphytic algal colonization is common in aquatic systems, but its interspecific competition remains poorly understood. In order to fill the gap, the process of periphytic algal colonization in the Middle Route of the South to North Water Diversion Project was studied. The results showed that the process was divided into three stages: the initial colonization stage (T1, 3-6 days), community formation stage (T2, 12-18 days) and primary succession stage (T3, 24-27 days). In T1, the dominant species were Diatoma vulgaris (Bory), Navicula phyllepta (Kützing) and Fragilaria amphicephaloides (Lange-Bertalot) belonging to Heterokontophyta; these species boasted wide niche widths (NWs), low niche overlap (NO) and low ecological response rates (ERRs). In T2, the dominant species were Diatoma vulgaris, Cymbella affinis (Kützing), Navicula phyllepta, Fragilaria amphicephaloides, Gogorevia exilis (Kützing), Melosira varians (C.Agardh), Phormidium willei (N.L.Gardner) and Cladophora rivularis (Kuntze). These species displayed wider NWs, lower NO, and lower ERRs than those in T1. In T3, the dominant species were Diatoma vulgaris, Cymbella affinis, Navicula phyllepta, Fragilaria amphicephaloides, Achnanthes exigu (Grunow), etc. Among them, Heterokontophyta such as Diatoma vulgaris and Cymbella affinis had a competitive advantage based on NWs and ERRs. Cyanobacteria like Phormidium willei lost their dominant status due to the narrower NW and the increased NO. It could be concluded the interspecific competition became fiercer and shaped the colonization process; this study will be helpful in understanding the colonization of periphytic algal communities.

Regeneration of post‐mining and post‐fire soil function by assessment of tree nutrient status: Evidence from pioneer and N‐fixing species

AbstractNutrient concentrations in the foliage of particular tree species can identify growth‐limiting factors. Therefore, the adaptability and usefulness of certain trees in the afforestation of barren soils after disturbances could be based on nutrient supply and stoichiometry. In this study, we investigated the macronutrient supply to (i.e., nitrogen [N], phosphorus [P], potassium, sulfur, calcium [Ca], and magnesium [Mg]) and C:N:P (carbon:nitrogen:phosphorus) stoichiometry of the foliage of black alder (Alnus glutinosa), common birch (Betula pendula), and Scots pine (Pinus sylvestris) in two different regeneration scenarios—a reclaimed mine site with primary succession and an afforested post‐fire (PF) site with secondary succession. The control plot was on an undisturbed forest site hosting stands of the studied tree species. The lower concentrations of elements in the post‐mining soils developed from “point zero” were enough to supply the trees with a similar level of nutrition to those in the PF and undisturbed soils. The studied tree species differed in their foliage chemistry and had different effects on the soil properties. The alder and birch foliage contained more nutrients than the pine foliage. In particular, the birch foliage contained the highest concentrations of Ca, Mg, and P, thus enhancing the biogeochemical cycling of these elements. The alder foliage had the highest N concentration, albeit the soil total N contents under this species were not higher than those under birch. Thus, its phytomeliorative effect may have been overestimated. The pine foliage contained the lowest concentrations of nutrients, indicating the high nutrient use efficiency of this species. On the sites degraded after disturbance, pine and birch grew under N‐limitation stress, while the alder—a N‐fixing species—grew under P‐limitation stress, especially at the PF site. The PF soils under alder were also characterized by higher acidity, P depletion, and higher C:P and N:P ratios compared to the PF soils under the other studied species. We found that birch should be the most common tree species in the first phase of area regeneration after disturbances. Introducing alder into afforestation should take place in admixtures, especially at the PF site.

The Temporal and Spatial Dynamics of Succession in a Glacial Foreland in Southern Iceland: The Effects of Landscape Heterogeneity

One of the more visible consequences of anthropogenic climate change is the ongoing retreat of glaciers worldwide. Rates of primary succession in the resulting glacial forelands are commonly calculated from a single measurement set using a single set of measurements across a landscape of varying age, but repeated measurements over decadal scales may be a more effective means of examining the rates and trends of colonization and community development. Repeated measurements of vegetation groups in a glacial foreland in southern Iceland demonstrate that successional changes are measurable, as shown by the calculation of the dissimilarity index at sites over a 15 year interval. Inter-site dissimilarity validates the essential paradigm of primary succession, where vegetative coverage increases in the glacial foreland as a function of time and supports earlier interpretations saying that species richness decreases on older surfaces, even as the total vegetation cover increases. However, successional processes are subject to major abiotic factors, such as aspect, which is controlled by landscape topography, and the substrate composition. The glacial moraines and outwash plain are underlain by different substrates which produce separate successional trajectories. Succession on the moraines ultimately produces a birch-shrub-heath community, while the outwash deposits promote development of a moss-heath community.

The Science of Vegetation with Reference to India

Pt. I Vegetation is the sum total of plant population covering a region and its descrete units circumscribed by characteristic environment, are communities. The species content is the flora. The physical and the biological surroundings characterise the environmental complex. Both plants and their environment are dynamic systems interacting within and with each other. The amplitude of variations in the environment is generally met with synchronised adaptive responses of the plants in time and space. Differentiation of ecads and ecotypes within the plastic species is the result. However, many forms and invaders may get eliminated also if the situation goes beyond their range of tolerance set by the genetic organisation as the factors may become critical at different stages of the life-cycle. The species around provide the genetic material for recruitment and ecesis within the community.pt. II Migration of species involving mobility of disseminules, their germination, aggregation, competition and final ecesis-ever continuing processes lead to colonisation and invasions. All these plant phenomena react upon the environment introducing changes therein. Thus newer community-environment-complex equilibria are set up in the dynamic system. The whole process is called, succession in relation to time and the series of succeeding communities for a given area, a sere. When it happens ‘de novo’ with no trace of plant present originally in the area, it is prisere as a result of primary succession and subsere with disturbed communities in which secondary succession is the rule. The mechanism of succession is driven by the reacting and changing environment consequential largely either to the plant processes themselves or to extraneous forces succession is autogenic in the former and allogenic in the latter case. In every case succession terminates into a more stable climax community generally dependant upon the climate and soil. The taxa used for classifying communities differ widely among ecologists but association is the basic unit accepted by all, though with varying concepts. The concept of ecosystem in relation to energy and matter within the community is the most acceptable basis for comprehending;vegetation types in India.Pt. III Since vegetation evolves out of the flora floristic regions of India should form the basis of its main divisions. For this purpose three main latitudinal belts viz. (1) Eastern and Western Himalayas, (2) Assam, Gangetic Plains and Rajasthan, and (3) Deccan and Malabar are recognised. The seven provinces with their distinct climate including photoperiod can be individually considered for the description of vegetation types along gradients of altitude, humidity-aridity, history and proximity of human settlements and soil fertility. Along these gradients closed, open and desert types of structure within forests, scrub and grass can be described with their combinations wherever necessary. Physiognomy, structure, function, composition, dynamics, habitat relations and history are the important diagnostic criteria of vegetation types. Size, texture and seasonal behaviour of leaves of dominant species may also be given. The hydrophytes can be described in each place as floating, suspended, submerged anchored, floating-leaved anchored and emergent anchored.

The roles of rare and abundant microbial species in the primary succession of biological soil crusts are differentiated in metal tailings ponds with different states

Tailings ponds formed by long-term accumulation of mineral processing waste have become a global environmental problem. Even worse, tailings ponds are often simply abandoned or landfilled after they cease to be used. This allows pollution to persist and continue to spread in the environment. The significance of primary succession mediated by biological soil crusts for tailings pond remediation has been illustrated by previous studies. However, the process of primary succession may not be the same at different stages during the lifetime of tailings ponds. Therefore, we investigated the environmental differences and the successional characteristics of microbial communities in the primary successional stage of tailings ponds at three different states. The results showed that the primary succession process positively changed the environment of tailings ponds in any state of tailings ponds. The primary successional stage determined the environmental quality more than the state of the tailings pond. In the recently abandoned tailings ponds, abundant species were more subjected to heavy metal stress, while rare species were mainly limited by nutrient content. We found that as the succession progressed, rare species gradually acquired their own community space and became more responsive to environmental stresses. Rare species played an important role in microbial keystone species groups.

Convergence effect during spatiotemporal succession of lacustrine plastisphere: loss of priority effects and turnover of microbial species.

Succession is a fundamental aspect of ecological theory, but studies on temporal succession trajectories and ecological driving mechanisms of plastisphere microbial communities across diverse colonization environments remain scarce and poorly understood. To fill this knowledge gap, we assessed the primary colonizers, succession trajectories, assembly, and turnover mechanisms of plastisphere prokaryotes and eukaryotes from four freshwater lakes. Our results show that differences in microbial composition similarity, temporal turnover rate, and assembly processes in the plastisphere do not exclusively occur at the kingdom level (prokaryotes and eukaryotes), but also depend on environmental conditions and colonization time. Thereby, the time of plastisphere colonization has a stronger impact on community composition and assembly of prokaryotes than eukaryotes, whereas for environmental conditions, the opposite pattern holds true. Across all lakes, deterministic processes shaped the assembly of the prokaryotes, but stochastic processes influenced that of the eukaryotes. Yet, they share similar assembly processes throughout the temporal succession: species turnover over time causes the loss of any priority effect, which leads to a convergent succession of plastisphere microbial communities. The increase and loss of microbial diversity in different kingdoms during succession in the plastisphere potentially impact the stability of entire microbial communities and related biogeochemical cycles. Therefore, research needs to integrate temporal dynamics along with spatial turnovers of the plastisphere microbiome. Taking the heterogeneity of global lakes and the diversity of global climate patterns into account, we highlight the urgency to investigate the spatiotemporal succession mechanism of plastisphere prokaryotes and eukaryotes in more lakes around the world.

Plant water source effects on plant-soil feedback for primary succession of terrestrial ecosystems in a glacier region in China

Despite the extensive research conducted on plant-soil-water interactions, the understanding of the role of plant water sources in different plant successional stages remains limited. In this study, we employed a combination of water isotopes (δ2H and δ18O) and leaf δ13C to investigate water use patterns and leaf water use efficiency (WUE) during the growing season (May to September 2021) in Hailuogou glacier forefronts in China. Our findings revealed that surface soil water and soil nutrient gradually increased during primary succession. Dominant plant species exhibited a preference for upper soil water uptake during the peak leaf out period (June to August), while they relied more on lower soil water sources during the post-leaf out period (May) or senescence (September to October). Furthermore, plants in late successional stages showed higher rates of water uptake from uppermost soil layers. Notably, there was a significant positive correlation between the percentage of water uptake by plants and available soil water content in middle and late stages. Additionally, our results indicated a gradual decrease in WUE with progression through succession, with shallow soil moisture utilization negatively impacting overall WUE across all succession stages. Path analysis further highlighted that surface soil moisture (0– 20 cm) and middle layer nutrient availability (20– 50 cm) played crucial roles in determining WUE. Overall, this research emphasizes the critical influence of water source selection on plant succession dynamics while elucidating underlying mechanisms linking succession with plant water consumption.

Facilitating early boreal forest succession on waste rock using Ramial Chipped Wood mulch: A five-year study

After a mine is closed, waste rock storage areas must be revegetated to facilitate the return of ecosystem services and meet legal and social expectations. The restoration of forest ecosystems on waste rock through spontaneous colonization associated with primary succession can take decades and is still poorly studied. Adding a mulch of ramial chipped wood (RCW) could improve the physicochemical properties and microclimate conditions of waste rock, thus facilitating substrate colonization by plants. In 2016, a fully randomized block design was installed on waste rock from a closed gold mine located in the boreal forest in Abitibi-Témiscamingue, Quebec, Canada. The design included four treatments: scarified waste rock as the control (WR), 2 cm of RCW mulch on top of scarified waste rock (RCW/WR), and 10 cm layer of sand on top of scarified waste rock with or without 2 cm of RCW mulch (RCW/S and S, respectively). Over a period of five years, we followed the natural colonization of forest species as well as abiotic (substrate microclimate conditions and physicochemistry) and biotic (herbaceous plant colonization) factors influencing woody plant colonization success. Six boreal woody species spontaneously colonized the area (five individuals per m2, on average, all species combined). Salix sp. and Picea glauca seedlings were more abundant on substrates with RCW mulch (especially sand) than those without mulch, and P. glauca had greater aerial biomasses with RCW mulch. Substrate water content during the growing season and the presence of the weed species Tussilago farfara were determining environmental factors in substrate colonization by Abies balsamea. In the absence of Tussilago farfara, RCW mulch increased A. balsamea colonization. RCW mulch increased the total cover of colonizing herbaceous plants (23.3–58.2%) as compared to mineral substrates alone (4.78–52.3%), which negatively affected the number of A. balsamea individuals. The colonizing herbaceous species were mostly primary succession species, Pilosella caespitosa, Anaphalis margaritacea, and Tussilago farfara being dominant; no exotic species were observed. The results highlight the potential of RCW mulch in promoting forest recolonization on waste rock, including mid-successional species like Picea sp., which could be useful for facilitating ecosystem succession in post-mining landscapes.

Phototrophic Nitrogen Fixation, a Neglected Biogeochemical Process in Mine Tailings?

Biological nitrogen fixation (BNF) has important ecological significance in mine tailing by contributing to the initial accumulation of nitrogen. In addition to chemolithotrophic and heterotrophic BNF, light may also fuel BNF in oligotrophic mine tailings. However, knowledge regarding the occurrence and ecological significance of this biogeochemical process in mine tailings remains ambiguous. The current study observed phototrophic BNF in enrichment cultures established from three primary successional stages (i.e., original tailings, biological crusts, and pioneer plants) of tailings. Notably, phototrophic BNF in tailings may be more active at vegetation stages (i.e., biological crusts and pioneering plants) than in bare tailings. DNA-stable isotope probing identified Roseomonas species as potential aerobic anoxygenic phototrophs responsible for phototrophic BNF. Furthermore, metagenomic binning as well as genome mining revealed that Roseomonas spp. contained essential genes involved in nitrogen fixation, anoxygenic photosynthesis, and carbon fixation, suggesting their genetic potential to mediate phototrophic BNF. A causal inference framework equipped with the structural causal model suggested that the enrichment of putative phototrophic diazotrophic Roseomonas may contribute to an elevated total nitrogen content during primary succession in these mine tailings. Collectively, our findings suggest that phototrophic diazotrophs may play important roles in nutrient accumulation and hold the potential to facilitate ecological succession in tailings.

Comparison of Microbial Diversity of Two Typical Volcanic Soils in Wudalianchi, China.

Volcanic lava is an excellent model of primary succession, in which basalt-associated microorganisms drive the cycling of different elements such as nitrogen, carbon, and other nutrients. Microbial communities in volcanic soils are of particular interest for study on the emergence and evolution of life within special and extreme conditions. The initial processes of colonization and subsequent rock weathering by microbial communities are still poorly understood. We analyzed the soil bacterial and fungal communities and diversities associated with lava (LBL) and kipuka (BK) sites in Wudalianchi using 16S and ITS rRNA Illumina Miseq sequencing techniques. The results showed that soil physical and chemical properties (pH, MC, TOC, TN, TP, AP, DOC, and DON) significantly differed between LBL and BK. The Shannon, Ace, and Pd indexes of fungi in the two sites showed a significant difference (p < 0.05). The dominant bacterial phyla forming communities at LBL and BK sites were Acidobacteria, Proteobacteria, Actinobacteria, and Basidiomycota, and their differences were driven by Gemmatimonadetes and Verrucomicrobia. The dominant fungal phyla of LBL and BK sites were Ascomycota, Zygomycota, and Rozellomcota, which differed significantly between the two sites. The microbial communities showed extremely significant differences (p < 0.05), with MC, pH, and nitrogen being the main influencing factors according to RDA/CCA and correlation analysis. Microbial functional prediction analysis across the two sites showed that the relative abundance of advantageous functional groups was significantly different (p < 0.05). The combined results drive us to conclude that the volcanic soil differences in the deposits appear to be the main factor shaping the microbial communities in Wudalianchi (WDLC) volcanic ecosystems.