Arbuscular mycorrhizal fungi (AMF) establish symbiotic interaction with 80% of known land plants. It has a pronounced impact on plant growth, water absorption, mineral nutrition, and protection from ...abiotic stresses. Plants are very dynamic systems having great adaptability under continuously changing drying conditions. In this regard, the function of AMF as a biological tool for improving plant drought stress tolerance and phenotypic plasticity, in terms of establishing mutualistic associations, seems an innovative approach towards sustainable agriculture. However, a better understanding of these complex interconnected signaling pathways and AMF-mediated mechanisms that regulate the drought tolerance in plants will enhance its potential application as an innovative approach in environmentally friendly agriculture. This paper reviews the underlying mechanisms that are confidently linked with plant-AMF interaction in alleviating drought stress, constructing emphasis on phytohormones and signaling molecules and their interaction with biochemical, and physiological processes to maintain the homeostasis of nutrient and water cycling and plant growth performance. Likewise, the paper will analyze how the AMF symbiosis helps the plant to overcome the deleterious effects of stress is also evaluated. Finally, we review how interactions between various signaling mechanisms governed by AMF symbiosis modulate different physiological responses to improve drought tolerance. Understanding the AMF-mediated mechanisms that are important for regulating the establishment of the mycorrhizal association and the plant protective responses towards unfavorable conditions will open new approaches to exploit AMF as a bioprotective tool against drought.
Nitrogen (N) availability is increasing dramatically in many ecosystems, but the influence of elevated N on the functioning of arbuscular mycorrhizal (AM) fungi in natural ecosystems is not well ...understood.
We measured AM fungal community structure and mycorrhizal function simultaneously across an experimental N addition gradient in an alpine meadow that is limited by N but not by phosphorus (P). AM fungal communities at both whole-plant-community (mixed roots) and single-plant-species (Elymus nutans roots) scales were described using pyro-sequencing, and the mycorrhizal functioning was quantified using a mycorrhizal-suppression treatment in the field (whole-plant-community scale) and a glasshouse inoculation experiment (single-plant-species scale).
Nitrogen enrichment progressively reduced AM fungal abundance, changed AM fungal community composition, and shifted mycorrhizal functioning towards parasitism at both whole-plant-community and E. nutans scales. N-induced shifts in AM fungal community composition were tightly linked to soil N availability and/or plant species richness, whereas the shifts in mycorrhizal function were associated with the communities of specific AM fungal lineages.
The observed changes in both AM fungal community structure and functioning across an N enrichment gradient highlight that N enrichment of ecosystems that are not P-limited can induce parasitic mycorrhizal functioning and influence plant community structure and ecosystem sustainability.
We measured the influences of soil fertility and plant community composition on Glomeromycota, and tested the prediction of the functional equilibrium hypothesis that increased availability of soil ...resources will reduce the abundance of arbuscular mycorrhizal (AM) fungi.
Communities of plants and AM fungi were measured in mixed roots and in Elymus nutans roots across an experimental fertilization gradient in an alpine meadow on the Tibetan Plateau.
As predicted, fertilization reduced the abundance of Glomeromycota as well as the species richness of plants and AM fungi. The response of the glomeromycotan community was strongly linked to the plant community shift towards dominance by Elymus nutans. A reduction in the extraradical hyphae of AM fungi was associated with both the changes in soil factors and shifts in the plant community composition that were caused by fertilization.
Our findings highlight the importance of soil fertility in regulating both plant and glomeromycotan communities, and emphasize that high fertilizer inputs can reduce the biodiversity of plants and AM fungi, and influence the sustainability of ecosystems.
Two subterranean ancient Chinese tombs of over 1700 years old, one from the Jin Dynasty and another from the Han Dynasty, were investigated in relation to black spots associated with microbiological ...deterioration of brick mural paintings within. The objectives of this study were to characterize the diversity of culturable fungal communities and assess the biodeteriorative potential of the isolated fungi. Culture-dependent methods using four different types of media were used for fungal isolation and specialized agar plates were used for biodeteriorative analyses by monitoring calcite dissolution, proteolytic activity, pH change, and biomineralization capabilities the isolated strains. Physical characterization of the mural samples and biomineralization were carried out using scanning electron microscopy combined with energy dispersive and X-ray diffraction analyses, while fungal acid production was analysed using High-performance liquid Chromatography (HPLC). Results showed that most of the 22 fungal strains isolated belonged to the Penicillium and Aspergillus genera. Differences in fungal community diversity between the two tombs may be attributed to variations in their interior temperature and relative humidity, however the history and drawing techniques used could also be contributing factors. Penicillium aurantiogriseum, Aspergillus versicolor and Penicillium olsonii were found in both tombs, representing the core microflora found in the black spots, thus these three fungi may be the sources of the black spots. More than 68% of the isolated fungi showed proteolytic activity and 27% of the strains produced acids, leading to dissolution of calcium carbonate and decreased pH value. Among the isolates, 5 out of 6 acid-forming fungal strains could also promote biomineralization. Penicillium was the main genus found to form acid and promote biomineralization. These fungi with biodeterioration and biomineralization characteristics were abundant in the black spots, indicating that formation of black spots was relevant to their presence and activity. These results suggest that thriving fungi, primarily driven by the local microenvironment, pose a high risk to brick wall paintings.
•Filamentous fungi contribute to the formation of black spots on mural paintings.•The decay of mural paintings through proteolysis, carbonate dissolution, acid production, and biomineralization.•The formation of black spots on mural is influenced by the surrounding microenvironmental conditions.•Using different methods in tandem should be a prerequisite for the precise assessment of fungal threats to mural paintings.
Microorganisms can accelerate the deterioration of stone monuments. In this study, we used next-generation sequencing (Illumina MiSeq PE300 Platform) to investigate the microbial biofilm communities ...that have developed on sandstone in two famous Buddhist cave temples, the Maijishan Grottoes and Tiantishan Grottoes, located on the historical Silk Road in western China. We found high bacterial diversity and relatively low eukaryota diversity based on 16S and 18S ribosomal RNA (rRNA) sequencing analysis. The dominant bacterial groups were Cyanobacteria, Actinobacteria, Proteobacteria, Bacteroidetes, and Chloroflexi. The dominant eukaryota were Ascomycota, Basidiomycota, and Chytridiomycota. The most dominant genes among the bacteria were from Cyanobacteria (unclassified and no rank), Pseudonocardia, Kribbella, and Rubrobacter; the dominant fungal genes were from unclassified Lecanorales and Capnodiales (unclassified and norank). These microbes form biofilms that will contribute to biodeterioration of the underlying sandstone. Combining with field monitoring and microscopic analysis, we determined that high bioreceptivity of the sandstone and locally available water were two important exogenous and endogenous factors that promoted microbial colonization, proliferation, and subsequent biofilm formation. The aforementioned microbes usually coexisted on the sandstone surfaces by building an inter-connected and dynamic community capable of adapting to and resisting the harsh local environmental conditions to survive and undergo succession.
•A comparative analysis of microbial communities of stone biofilms of the two Grottoes.•High bioreceptivity of sandstone and available water are two of the most important factors for biofilm formation.•Strongly positive intra-domain connections contributed to resistance to harsh environment.
Plant pectin methyl-esterase (PME) and PME inhibitor (PMEI) belong to large gene families whose members are proposed to be widely involved in growth, development, and stress responses; however, the ...biological functions of most PMEs and PMEIs have not been characterized. In this study, we studied the roles of CbPMEI1, a cold-induced pectin methyl-esterase inhibitor (PMEI) gene from Chorispora bungeana, under freezing and salt stress. The putative CbPMEI1 peptide shares highest similarity (83%) with AT5G62360 (PMEI13) of Arabidopsis. Overexpression of either CbPMEI1 or PMEI13 in Arabidopsis decreased tissue PME activity and enhanced the degree of methoxylation of cell wall pectins, indicating that both genes encode functional PMEIs. CbPMEI1 and PMEI13 were induced by cold but repressed by salt stress and abscisic acid, suggesting distinct roles of the genes in freezing and salt stress tolerance. Interestingly, transgenic Arabidopsis plants overexpressing CbPMEI1 or PMEI13 showed decreased freezing tolerance, as indicated by survival and electrolyte leakage assays. On the other hand, the salt tolerance of transgenic plants was increased, showing higher rates of germination, root growth, and survival under salinity conditions as compared with non-transgenic wild-type plants. Although the transgenic plants were freezing-sensitive, they showed longer roots than wild-type plants under cold conditions, suggesting a role of PMEs in balancing the trade-off between freezing tolerance and growth. Thus, our study indicates that CbPMEI1 and PMEI13 are involved in root growth regulation under cold and salt stresses, and suggests that PMEIs may be potential targets for genetic engineering aimed to improve fitness of plants under stress conditions.
Defining response groups within N-related microbial communities is needed to predict land management effect on soil N dynamics, but information on such response groups and associated environmental ...drivers is scarce. We investigated the abundance and major populations of ammonia-oxidizing archaea (AOA) and bacteria (AOB), and nirS- and nirK-harboring denitrifiers under different grazing managements in Tibetan alpine meadow soils. Grazing increased AOB and AOA abundances up to 42 fold and 3.7 fold, respectively, and increased the percentage of AOB within total ammonia oxidizers from 3.1% to 10.8%. The abundance of nirK-like denitrifiers increased with grazing intensity, while the abundance of nirS-like denitrifiers tended to decrease. However, sub-groups within each of these broad groups of (de)nitrifiers responded differently to grazing. Soil nitrate was the main driver of the abundance of denitrifier sub-groups (nirK or nirS) positively responding to grazing, while soil moisture and carbon concentration were the main drivers of the abundance of denitrifier sub-groups negatively responding to grazing. AOB and nirK-harboring denitrifiers thus generally responded more positively to grazing than AOA and nirS-harboring denitrifiers, but significant functional diversity existed within each group. Our approach demonstrates the usefulness of the concept of response groups to better characterize and understand (de)nitrifier response to grazing.
•Sub-groups of (de)nitrifiers respond differently to grazing in grassland soil.•Grazing promoted more AOB and nirK denitrifiers than AOA and nirS denitrifiers.•Different response groups exist within AOB, AOA, and nirK and nirS denitrifiers.•Predicting grazing effect requires to account for intra-group functional diversity.•The response group concept helps understanding (de)nitrifier response to grazing.
The availability of limiting nutrients plays a crucial role in shaping communities of endophytes. Moreover, whether fungal endophytes are host-specific remains controversial. We hypothesized that in ...a harsh and nitrogen (N)-deficient area, diversity and community composition of foliar endophytic fungi (FEFs) varied substantially among plots with experimentally elevated levels of macronutrients, and thus, N availability, instead of host species identity, would have a greater influence in structuring fungal communities at different scales. We also expected an important subset of taxa shared among numerous host species and N gradients to form a community-wide core microbiome. We measured the leaf functional traits and community structures of FEFs of three commonly seen species in an alpine meadow nested with a long-term N fertilization experiment. We found that host plant identity was a powerful factor driving the endophytic fungal community in leaves, even in habitats where productivity was strongly limited by nitrogen (
p
< 0.001). We also found that within the same host, nitrogen was an important driving force for the composition of the endophytic fungi community (
p
< 0.05). In addition, the leaf carbon content was the most important functional trait that limited the diversity of endophytic fungi (
p
< 0.001). Finally, we documented a distinct core microbiome shared among our three focal species and N gradients.
Background
Microbial colonization represents one of the main threats to the conservation of subterranean cultural heritage sites. Recently, the microbial colonization on murals in tombs has gradually ...attracted attention.
Methods
In this study, a total of 33 samples, including 27 aerosol samples and 6 mural painting samples, were collected from different sites of Xu Xianxiu’s Tomb and analyzed using culture-dependent methods. We compared the diversities of culturable bacteria and fungi isolated from the air and murals and explored the potential impacts of microorganisms on the biodeterioration of the murals.
Results
Phylogenetic analyses revealed that the culturable bacteria belonged to Bacillus, Microbacterium, Lysobacter and Arthrobacter. And the most of fungal belonged to the Penicillium, Cladosporium and Aspergillus genera. The composition and structure of airborne bacteria and fungi outside the tomb were both significantly different from that inside the tomb. The variation trends of airborne bacterial and fungal concentrations at different sampling sites were remarkably similar. Bacillus frigoritolerans, Bacillus halotolerans, Bacillus safensis, Exiguobacterium mexicanum, Microbacterium trichothecenolyticum, and Micrococcus yunnanensis were bacterial species commonly isolated from both the mural and air environments. Fungal species commonly isolated from aerosol samples and mural painting samples were Alternaria alternata, Cladosporium cladosporioides, Penicillium brevicompactum, and Peyronellaea glomerata. The prediction of the ecological functions of the bacteria revealed that chemoheterotrophy or aerobic_chemoheterotrophy accounted for substantial relative proportions in all sample types.
Conclusion
These results suggest that the aerosol circulation between the inside and outside environments of the tomb was weak and that the outside environment had yet to have an impact on the air microbial community inside the tomb. Selective colonization of microorganisms, which is mediated by interaction between microorganisms and special microenvironmental factors, is an important reason for the biodeterioration of murals.
Tiantishan Grottoes, a famous site well known for its historical status in the spread of Buddhism art in ancient China, were selected for a comparison and analysis of microbial taxonomic ...characteristics on the wall paintings under different preservation conditions: in situ and ex situ conservation. A total of 12 samples were collected from three different cave wall paintings preserved in situ or ex situ. The 16/18S rRNA gene-based sequences revealed a high bacterial diversity and a relative low fungal abundance, including bacterial groups Firmicutes, Actinobacteria, Proteobacteria, Bacteroidetes, Cyanobacteria, Acidobacteria, Deinococcus-Thermus and Fusobacteria; and fungal groups Ascomycota and Basidiomycota. Among them, two bacterial genera of the Promicromonospora and Planomicrobium and fungal order of the Sordariales and the family of Trichocomaceae were dominant in the samples preserved ex situ. Some of them have been reported at other cultural heritage sites and associated with the biodeterioration of cultural relics. The over-growth of these microbes led to the abundant filaments formed visible on the surface of the ex situ wall paintings, which preserved under museum conditions. Application of preservation materials including animal glue and wet gypsum to take them off from grottoes and strengthen, and subsequent long-term preservation under poor conditions in museums were mainly responsible for the microbial outbreaks. To avoid similar problems in the future, reasonable intervention measures and strict micro-environmental control must be implemented to the ex situ preservation of wall paintings. Our results have profound significance for clarify the occurrence of microbial invasions and mechanisms on the wall paintings; it is helpful to development a reasonable artificial intervention measures for conservation work of the wall paintings in the future.
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•Comparative analysis of the microflora on murals between in situ and ex situ of the Tiantishan Grottoes.•Artificial intervention and non-ideal conditions were results in the biodeterioration of the ex situ protection murals.•Avoidance of input nutrients and water and strict controls of the micro-climate for the ex situ protection of the murals.
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