Seasonal comparison of bacterial communities in rhizosphere of alpine cushion plants in the Himalayan Hengduan Mountains

Biodiversity in mountain soils above the treeline

Biological diversity in mountain ecosystems has been increasingly studied over the last decade. This is also the case for mountain soils, but no study to date has provided an overall synthesis of the current state of knowledge. Here we fill this gap with a first global analysis of published research on cryptogams, microorganisms, and fauna in mountain soils above the treeline, and a structured synthesis of current knowledge. Based on a corpus of almost 1400 publications and the expertise of 37 mountain soil scientists worldwide, we summarise what is known about the diversity and distribution patterns of each of these organismal groups, specifically along elevation, and provide an overview of available knowledge on the drivers explaining these patterns and their changes. In particular, we document an elevation-dependent decrease in faunal diversity above the treeline, while for cryptogams there is an initial increase above the treeline, followed by a decrease towards the nival belt. Thus, our data confirm the key role that elevation plays in shaping the biodiversity and distribution of these organisms in mountain soils. The response of prokaryote diversity to elevation, in turn, was more diverse, whereas fungal diversity appeared to be substantially influenced by plants. As far as available, we describe key characteristics, adaptations, and functions of mountain soil species, and despite a lack of ecological information about the uncultivated majority of prokaryotes, fungi, and protists, we illustrate the remarkable and unique diversity of life forms and life histories encountered in alpine mountain soils. By applying rule- as well as pattern-based literature-mining approaches and semi-quantitative analyses, we identified hotspots of mountain soil research in the European Alps and Central Asia and revealed significant gaps in taxonomic coverage, particularly among biocrusts, soil protists, and soil fauna. We further report thematic priorities for research on mountain soil biodiversity above the treeline and identify unanswered research questions. Building upon the outcomes of this synthesis, we conclude with a set of research opportunities for mountain soil biodiversity research worldwide. Soils in mountain ecosystems above the treeline fulfil critical functions and make essential contributions to life on land. Accordingly, seizing these opportunities and closing knowledge gaps appears crucial to enable science-based decision making in mountain regions and formulating laws and guidelines in support of mountain soil biodiversity conservation targets.

Amplicon sequencing and culture-dependent approaches reveal core bacterial endophytes aiding freezing stress tolerance in alpine Rosaceae plants

Wild plants growing in alpine regions are associated with endophytic microbial communities that may support plant growth and survival under cold conditions. The structure and function of endophytic bacterial communities were characterized in flowers, leaves, and roots of three alpine Rosaceae plants in Alpine areas using a combined amplicon sequencing and culture-dependent approaches to determine the role of core taxa on plant freezing stress tolerance. Amplicon sequencing analysis revealed that plant tissue, collection site, and host plant are the main factors affecting the richness, diversity, and taxonomic structure of endophytic bacterial communities in alpine Rosaceae plants. Core endophytic bacterial taxa were identified as 31 amplicon sequence variants highly prevalent across all plant tissues. Psychrotolerant bacterial endophytes belonging to the core taxa of Duganella, Erwinia, Pseudomonas, and Rhizobium genera mitigated freezing stress in strawberry plants, demonstrating the beneficial role of endophytic bacterial communities and their potential use for cold stress mitigation in agriculture.IMPORTANCEFreezing stress is one of the major abiotic stresses affecting fruit production in Rosaceae crops. Current strategies to reduce freezing damage include physical and chemical methods, which have several limitations in terms of costs, efficacy, feasibility, and environmental impacts. The use or manipulation of plant-associated microbial communities was proposed as a promising sustainable approach to alleviate cold stress in crops, but no information is available on the possible mitigation of freezing stress in Rosaceae plants. A combination of amplicon sequencing, culture-dependent, and plant bioassay approaches revealed the beneficial role of the endophytic bacterial communities in alpine Rosaceae plants. In particular, we showed that culturable psychrotolerant bacterial endophytes belonging to the core taxa of Duganella, Erwinia, Pseudomonas, and Rhizobium genera can mitigate freezing stress on strawberry seedlings. Overall, this study demonstrates the potential use of psychrotolerant bacterial endophytes for the development of biostimulants for cold stress mitigation in agriculture.

Decoupled responses of soil microbial diversity and ecosystem functions to successive degeneration processes in alpine pioneer community

Many alpine ecosystems are undergoing vegetation degradation because of global changes, which are affecting ecosystem functioning and biodiversity. The ecological consequences of alpine pioneer community degradation have been less studied than glacial retreat or meadow degradation in alpine ecosystems. We document the comprehensive responses of microbial community characteristics to degradation processes using field-based sampling, conduct soil microcosm experiments to simulate the effects of global change on microorganisms, and explore their relationships to ecosystem functioning across stages of alpine pioneer community degradation. Our work provides the first evidence that alpine pioneer community degradation led to declines of 27% in fungal richness, 8% in bacterial richness, and about 50% in endemic microorganisms. As vegetation degraded, key ecosystem functions such as nutrient availability, soil enzymatic activity, microbial biomass, and ecosystem multifunctionality progressively increased. However, soil respiration rate and carbon storage exhibited unbalanced dynamics. Respiration rate increased by 190% during the middle stage of degradation compared with the primary stage, and it decreased by 38% in the later stage. This indicates that soil carbon loss or emission increases during the mid-successional stage, whereas in later successional stages, alpine meadows become significant carbon sinks. Compared with microbial community characteristics (such as richness of total and functional taxa, and network complexity), community resistance contributes more significantly to ecosystem functions. Especially, the bacterial community resistance is crucial for ecosystem functioning, yet it is greatly impaired by nitrogen addition. Based on microbial network, community assembly, and community resistance analyses, we conclude that fungi are more vulnerable to environmental changes and show smaller contributions to ecosystem functions than bacteria in degrading alpine ecosystems. Our findings enhance the knowledge of the distinct and synergistic functional contributions of microbial communities in degrading alpine ecosystems and offer guidance for developing restoration strategies that optimize ecosystem functioning of degraded alpine plant communities.

In Situ Nano-SiO2 Electrospun Polyethylene-Oxide-Based Nano-Fiber Composite Solid Polymer Electrolyte for High-Performance Lithium-Ion Batteries

Polyethylene oxide (PEO)-based composite polymer electrolytes (CPEs) containing in situ SiO₂ fillers are prepared using an electrostatic spinning method at room temperature. Through the in situ hydrolysis of tetraethyl silicate (TEOS), the generated SiO₂ nanospheres are uniformly dispersed in the PEO matrix to form a 3D ceramic network, which enhances the mechanical properties of the electrolyte as a reinforcing phase. The interaction between SiO₂ nanospheres and PEO chains results in chemical bonding with a decrease in the crystallinity of the PEO matrix, as well as the complexation strength of PEO chains with lithium ions during the hydrolysis process. Meanwhile, the addition of SiO₂ nanospheres can disturb the orderliness of PEO chain segments and further suppress the crystallization of the PEO matrix. Therefore, improved mechanical/electrochemical properties can be obtained in the as-spun electrolyte with the unique one-dimensional high-speed ion channels. The electrospun CPE with in situ SiO₂ (10 wt%, ca. 45 nm) has a higher ionic conductivity of 1.03 × 10^-3 S cm^-1 than that of the mechanical blending one. Meanwhile, the upper limit of the electrochemical stability window is up to 5.5 V versus Li⁺/Li, and a lithium-ion migration number can be of up to 0.282 at room temperature. In addition, in situ SiO₂ electrospun CPE achieves a tensile strength of 1.12 MPa, elongation at the break of 488.1%, and it has an excellent plasticity. All in all, it is expected that the electrospun CPE prepared in this study is a promising one for application in an all-solid-state lithium-ion battery (LIB) with a high energy density, long life cycle, and high safety.

Ecology and potential functions of plant-associated microbial communities in cold environments

Complex microbial communities are associated with plants and can improve their resilience under harsh environmental conditions. In particular, plants and their associated communities have developed complex adaptation strategies against cold stress. Although changes in plant-associated microbial community structure have been analysed in different cold regions, scarce information is available on possible common taxonomic and functional features of microbial communities across cold environments. In this review, we discuss recent advances in taxonomic and functional characterization of plant-associated microbial communities in three main cold regions, such as alpine, Arctic and Antarctica environments. Culture-independent and culture-dependent approaches are analysed, in order to highlight the main factors affecting the taxonomic structure of plant-associated communities in cold environments. Moreover, biotechnological applications of plant-associated microorganisms from cold environments are proposed for agriculture, industry and medicine, according to biological functions and cold adaptation strategies of bacteria and fungi. Although further functional studies may improve our knowledge, the existing literature suggest that plants growing in cold environments harbor complex, host-specific and cold-adapted microbial communities, which may play key functional roles in plant growth and survival under cold conditions.

Cushion plants as critical pioneers and engineers in alpine ecosystems across the Tibetan Plateau

Cushion plants are widely representative species in the alpine ecosystem due to their vital roles in influencing abiotic and biotic environments, ecological succession processes, and ecosystem engineering. Importantly, cushion plants, such as Androsace L. and Arenaria L., are considered to be critical pioneers of ecosystem health, restoration, and sustainability across the Tibetan Plateau. This is because cushion plants (a) show tenacious vitality and can modify regional climates, substrates, and soil nutrients in extreme environments; (b) facilitate relationships with the surroundings and maintain the diversity of aboveground and belowground communities; and (c) are highly sensitive to environmental changes and thus can indicate grassland ecosystem health and resilience in the context of global change.

Exploring Actinobacteria Associated With Rhizosphere and Endosphere of the Native Alpine Medicinal Plant Leontopodium nivale Subspecies alpinum

The rhizosphere of plants is enriched in nutrients facilitating growth of microorganisms, some of which are recruited as endophytes. Endophytes, especially Actinobacteria, are known to produce a plethora of bioactive compounds. We hypothesized that Leontopodium nivale subsp. alpinum (Edelweiss), a rare alpine medicinal plant, may serve as yet untapped source for uncommon Actinobacteria associated with this plant. Rhizosphere soil of native Alpine plants was used, after physical and chemical pre-treatments, for isolating Actinobacteria. Isolates were selected based on morphology and identified by 16S rRNA gene-based barcoding. Resulting 77 Actinobacteria isolates represented the genera Actinokineospora, Kitasatospora, Asanoa, Microbacterium, Micromonospora, Micrococcus, Mycobacterium, Nocardia, and Streptomyces. In parallel, Edelweiss plants from the same location were surface-sterilized, separated into leaves, roots, rhizomes, and inflorescence and pooled within tissues before genomic DNA extraction. Metagenomic 16S rRNA gene amplicons confirmed large numbers of actinobacterial operational taxonomic units (OTUs) descending in diversity from roots to rhizomes, leaves and inflorescences. These metagenomic data, when queried with isolate sequences, revealed an overlap between the two datasets, suggesting recruitment of soil bacteria by the plant. Moreover, this study uncovered a profound diversity of uncultured Actinobacteria from Rubrobacteridae, Thermoleophilales, Acidimicrobiales and unclassified Actinobacteria specifically in belowground tissues, which may be exploited by a targeted isolation approach in the future.