Different mechanisms underlie similar species-area relationships in two tropical archipelagoes.

Despite much research in the field of island biogeography, mechanisms regulating insular diversity remain elusive. Here, we aim to explore mechanisms underlying plant species-area relationships in two tropical archipelagoes in the South China Sea. We found positive plant species-area relationships for both coral and continental archipelagoes. However, our results showed that different mechanisms contributed to similar plant species-area relationships between the two archipelagoes. For coral islands, soil nutrients and spatial distance among communities played major roles in shaping plant community structure and species diversity. By contrast, the direct effect of island area, and to a lesser extent, soil nutrients determined plant species richness on continental islands. Intriguingly, increasing soil nutrients availability (N, P, K) had opposite effects on plant diversity between the two archipelagoes. In summary, the habitat quality effect and dispersal limitation are important for regulating plant diversity on coral islands, whereas the passive sampling effect, and to a lesser extent, the habitat quality effect are important for regulating plant diversity on continental islands. More generally, our findings indicate that island plant species-area relationships are outcomes of the interplay of both niche and neutral processes, but the driving mechanisms behind these relationships depends on the type of islands.

New sesquiterpenoids from Biscogniauxia sp.

Five new sesquiterpenoids, including a campherenane-type (1), a bergamotane-type (2), a drimane-type (3), and two bisabolane-type (5-6) sesquiterpenoids have been isolated from Biscogniauxia sp. 71-10-1-1. Their structures were determined by spectroscopic analyses, quantum chemical ECD calculations,13C chemical shifts calculations, and X-ray crystallography. This is the first report of campherenane-type and drimane-type sesquiterpenoids from Biscogniauxia. Furthermore, the anti-inflammatory assays of all compounds are evaluated, and the results showed that compounds 3 and 7 exhibited the effects against the production of the pro-inflammatory cytokine TNF-α.

Bacterial genome size and gene functional diversity negatively correlate with taxonomic diversity along a pH gradient.

Bacterial gene repertoires reflect adaptive strategies, contribute to ecosystem functioning and are limited by genome size. However, gene functional diversity does not necessarily correlate with taxonomic diversity because average genome size may vary by community. Here, we analyse gene functional diversity (by shotgun metagenomics) and taxonomic diversity (by 16S rRNA gene amplicon sequencing) to investigate soil bacterial communities along a natural pH gradient in 12 tropical, subtropical, and temperate forests. We find that bacterial average genome size and gene functional diversity decrease, whereas taxonomic diversity increases, as soil pH rises from acid to neutral; as a result, bacterial taxonomic and functional diversity are negatively correlated. The gene repertoire of acid-adapted oligotrophs is enriched in functions of signal transduction, cell motility, secretion system, and degradation of complex compounds, while that of neutral pH-adapted copiotrophs is enriched in functions of energy metabolism and membrane transport. Our results indicate that a mismatch between taxonomic and functional diversity can arise when environmental factors (such as pH) select for adaptive strategies that affect genome size distributions.

Lower triangle factor based sliding mode observers design for T-S fuzzy systems with faults.

The paper mainly focuses on the fault estimation for a class of Takagi-Sugeno (T-S) fuzzy systems with faults. A synthetic estimation observer design method is proposed. The synthetic estimation observer can cover the robust observer, adaptive observer and intermediate estimation observer in the existing study work. Based on the observer design method, an LTF-based sliding mode observer (SMO) is designed for the T-S fuzzy system in consideration. Under the observer, the fault occurring in the system can be well estimated. The obtained LMI-based conditions guarantee the states of the error dynamics to be uniformly ultimately bounded. A numerical example tests the proposed method.

Community Assembly of Fungi and Bacteria along Soil-Plant Continuum Differs in a Zoige Wetland.

Distinct plant associated microbiomes live in rhizosphere soil, roots, and leaves. However, the differences in community assembly of fungi and bacteria along soil-plant continuum are less documented in ecosystems. We examined fungal and bacterial communities associated with leaves, roots, and rhizosphere soil of the dominant arbuscular mycorrhizal (AM) plants Taraxacum mongolicum and Elymus nutans and non-AM plant Carex enervis in the Zoige Wetland by using high throughput sequencing techniques. The operational taxonomic unit (OTU) richness of fungi and bacteria was significantly higher in rhizosphere soil than in roots and leaves, and their community compositions were significantly different in the rhizosphere soil, roots, and leaves in each plant species. The co-occurrence network analysis revealed that the sensitive fungal and bacterial OTUs with various taxonomic positions were mainly clustered into different modules according to rhizosphere soil, roots, and leaves in each plant species. Along the soil-plant continuum, the rhizosphere soil pool contributed more source on bacterial than on fungal communities in roots and leaves of the three plant species, and more source on bacterial and fungal communities in leaves of T. mongolicum and E. nutans compared with C. enervis. Furthermore, the root pool contributed more source on bacterial than on fungal communities in leaves of T. mongolicum and E. nutans but not that of C. enervis. This study highlights that the host plant selection intensity is higher in fungal than in bacterial communities in roots and leaves from rhizosphere soil in each plant species, and differs in fungal and bacterial communities along the soil-plant continuum in AM plants T. mongolicum and E. nutans and non-AM plant C. enervis in the Zoige Wetland. IMPORTANCE Elucidating the community microbiome assemblage alone the soil-plant continuum will help to better understand the biodiversity maintenance and ecosystem functioning. Here, we examined the fungal and bacterial communities in rhizosphere soil, roots, and leaves of two dominant AM plants and a non-AM plant in Zoige Wetland. We found that along the soil - plant continuum, host plant selection intensity is higher in fungal than in bacterial communities in roots and leaves from rhizosphere soil in each plant species, and differs in fungal and bacterial communities in the AM- and non-AM plants. This is the first report provides evidence of different assembly patterns of fungal and bacterial communities along the soil-plant continuum in the AM- and non-AM plants in the Zoige Wetland.

Nitrogen fertilisation disrupts the temporal dynamics of arbuscular mycorrhizal fungal hyphae but not spore density and community composition in a wheat field.

Elucidating the temporal dynamics of arbuscular mycorrhizal (AM) fungi is critical for understanding their functions. Furthermore, research investigating the temporal dynamics of AM fungi in response to agricultural practices remains in its infancy. We investigated the effect of nitrogen fertilisation and watering reduction on the temporal dynamics of AM fungi, across the lifespan of wheat. Nitrogen fertilisation decreased AM fungal spore density (SD), extraradical hyphal density (ERHD), and intraradical colonisation rate (IRCR) in both watering conditions. Nitrogen fertilisation affected AM fungal community composition in soil but not in roots, regardless of watering conditions. The temporal analysis revealed that AM fungal ERHD and IRCR were higher under conventional watering and lower under reduced watering in March than in other growth stages at low (≤ 70 kg N ha-1 yr-1 ) but not at high (≥ 140) nitrogen fertilisation levels. AM fungal SD was lower in June than in other growth stages and community composition varied with plant development at all nitrogen fertilisation levels, regardless of watering conditions. This study demonstrates that high nitrogen fertilisation levels disrupt the temporal dynamics of AM fungal hyphal growth but not sporulation and community composition.

Tree mycorrhizal type and tree diversity shape the forest soil microbiota.

There is limited knowledge on how the association of trees with different mycorrhizal types shapes soil microbial communities in the context of changing tree diversity levels. We used arbuscular (AM) and ectomycorrhizal (EcM) tree species as con- and heterospecific tree species pairs (TSPs), which were established in plots of three tree diversity levels including monocultures, two-species mixtures and multi-tree species mixtures in a tree diversity experiment in subtropical China. We found that the tree mycorrhizal type had a significant effect on fungal but not bacterial alpha diversity. Furthermore, only EcM but not AM TSPs fungal alpha diversity increased with tree diversity, and the differences between AM and EcM TSPs disappeared in multi-species mixtures. Tree mycorrhizal type, tree diversity and their interaction had significant effects on fungal community composition. Neither fungi nor bacteria showed any significant compositional variation in TSPs located in multi-species mixtures. Accordingly, the most influential taxa driving the tree mycorrhizal differences at low tree diversity were not significant in multi-tree species mixtures. Collectively, our results indicate that tree mycorrhizal type is an important factor determining the diversity and community composition of soil microbes, and higher tree diversity levels promote convergence of the soil microbial communities. SIGNIFICANCE STATEMENT: More than 90% of terrestrial plants have symbiotic associations with mycorrhizal fungi which could influence the coexisting microbiota. Systematic understanding of the individual and interactive effects of tree mycorrhizal type and tree species diversity on the soil microbiota is crucial for the mechanistic comprehension of the role of microbes in forest soil ecological processes. Our tree species pair (TSP) concept coupled with random sampling within and across the plots, allowed us the unbiased assessment of tree mycorrhizal type and tree diversity effects on the tree-tree interaction zone soil microbiota. Unlike in monocultures and two-species mixtures, we identified species-rich and converging fungal and bacterial communities in multi-tree species mixtures. Consequently, we recommend planting species-rich mixtures of EcM and AM trees, for afforestation and reforestation regimes. Specifically, our findings highlight the significance of tree mycorrhizal type in studying 'tree diversity - microbial diversity - ecosystem function' relationships.

Two New Diterpenoids from Biscogniauxia sp. and Their Activities.

Two new diterpenoids, including a seco-isopimarane type (1) and an abietane type (2), were isolated from Biscogniauxia sp. (71-10-1-1). Their structures, including absolute configurations, were elucidated by NMR spectroscopic analyses, X-ray crystallography, 13C chemical shifts calculations, and ECD calculations. This is the first report of diterpenoids from Biscogniauxia sp. Furthermore, short-term memory enhancement against Alzheimer's disease (AD), anti-inflammatory, and cytotoxic activities of 1-2 were also evaluated. The results showed that compound 1 exhibited short-term memory enhancement activity against AD.

Diisoprenyl-cyclohexene/ane-Type Meroterpenoids from Biscogniauxia sp. and Their Anti-inflammatory Activities.

A secondary metabolites investigation on Biscogniauxia sp. 71-10-1-1 was carried out, which led to the obtention of nine new diisoprenyl-cyclohexene/ane-type meroterpenoids (1-9) and two new isoprenylbenzoic acid-type meroterpeniods (10-11). The structures of these isolates were established on the basis of multispectroscopic analyses, ECD, and 13C chemical shifts calculations, and single-crystal X-ray diffraction. Among them, biscognin A (1) is the first diisoprenyl-cyclohexene-type meroterpenoid with a unique 2-isopropyl-6'-methyloctahydro-1'H-spiro[cyclopropane-1,2'-naphthalene] skeleton. Biscognienyne F (5) is the first diisoprenyl-cyclohexene-type meroterpenoid with a cyclic carbonate. The anti-inflammatory assays of the majority of compounds were evaluated, which exhibited that compounds 3 and 5 can obviously inhibit pro-inflammatory cytokines TNF-α and IL-6 productions. This is the first report for diisoprenyl-cyclohexene-type meroterpenoids with anti-inflammatory activity. Moreover, the possible biogenetic pathways of the majority of compounds (1-5) are proposed.

Assembly processes lead to divergent soil fungal communities within and among 12 forest ecosystems along a latitudinal gradient.

Latitudinal gradients provide opportunities to better understand soil fungal community assembly and its relationship with vegetation, climate, soil and ecosystem function. Understanding the mechanisms underlying community assembly is essential for predicting compositional responses to changing environments. We quantified the relative importance of stochastic and deterministic processes in structuring soil fungal communities using patterns of community dissimilarity observed within and between 12 natural forests and related these to environmental variation within and among sites. The results revealed that whole fungal communities and communities of arbuscular and ectomycorrhizal fungi consistently exhibited divergent patterns but with less divergence for ectomycorrhizal fungi at most sites. Within those forests, no clear relationships were observed between the degree of divergence within fungal and plant communities. When comparing communities at larger spatial scales, among the 12 forests, we observed distinct separation in all three fungal groups among tropical, subtropical and temperate climatic zones. Soil fungal ß-diversity patterns between forests were also greater when comparing forests exhibiting high environmental heterogeneity. Taken together, although large-scale community turnover could be attributed to specific environmental drivers, the differences among fungal communities in soils within forests was high even at local scales.

Soil fungal diversity and community assembly: affected by island size or type?

Fungi have a huge biodiversity and play important roles in soil biogeochemical cycling in island ecosystems. Although island biogeography has been widely studied for macroorganisms, fungal community assembly in true islands and its relationship with island area are less documented. We examined soil fungal communities in 18 oceanic islands of two types (eight non-coral islands and 10 coral islands) using the Illumina MiSeq sequencing technique. Our results showed that fungal α-diversity (species richness) was substantially different among the oceanic islands, with a higher value in non-coral islands than in coral islands. Fungal α-diversity was significantly affected by soil potassium and magnesium (Mg) and plant communities in non-coral islands, whereas only soil Mg significantly affected it in coral islands. Soil fungal community composition was significantly different in the non-coral and coral islands and was influenced by soil property, plant community and spatial distance. The ecological stochasticity model showed that the fungal community assembly was mainly governed by deterministic processes regardless of island type. Fungal ß-diversity, but not α-diversity, increased significantly with increasing island area. These findings have implications for the better prediction of soil fungal community dynamics in island systems and biodiversity conservation in fragmented habitats.

Response of arbuscular mycorrhizal fungal community in soil and roots to grazing differs in a wetland on the Qinghai-Tibet plateau.

Grazing as one of the most important disturbances affects the abundance, diversity and community composition of arbuscular mycorrhizal (AM) fungi in ecosystems, but the AM fungi in response to grazing in wetland ecosystems remain poorly documented. Here, we examined AM fungi in roots and soil in grazing and non-grazing plots in Zoige wetland on the Qinghai-Tibet plateau. Grazing significantly increased AM fungal spore density and glomalin-related soil proteins, but had no significant effect on the extra radical hyphal density of AM fungi. While AM fungal richness and community composition differed between roots and soil, grazing was found to influence only the community composition in soil. This study shows that moderate grazing can increase the biomass of AM fungi and soil carbon sequestration, and maintain the AM fungal diversity in the wetland ecosystem. This finding may enhance our understanding of the AM fungi in response to grazing in the wetland on the Qinghai-Tibet plateau.

Host identity is more important in structuring bacterial epiphytes than endophytes in a tropical mangrove forest.

Interactions between plants and microbes are involved in biodiversity maintenance, community stability and ecosystem functioning. However, differences in the community and network structures between phyllosphere epiphytic and endophytic bacteria have rarely been investigated. Here, we examined phyllosphere epiphytic and endophytic bacterial communities of six mangrove species using Illumina MiSeq sequencing of the 16S rRNA gene. The results revealed that the community structure of epiphytic and endophytic bacteria was different. Plant identity significantly affected the diversity and community structure of both epiphytic and endophytic bacteria, with a greater effect on the community structure of the former than the latter. Network analysis showed that both plant-epiphytic and plant-endophytic bacterial network structures were characterized by significantly highly specialized and modular but lowly connected and anti-nested properties. Furthermore, the epiphytic bacterial network was more highly specialized and modular but less connected and more strongly anti-nested than the endophytic bacterial network. This study reveals that the phyllosphere epiphytic and endophytic bacterial community structures differ and plant identity has a greater effect on the epiphytic than on the endophytic bacteria, which may provide a comprehensive insight into the role of plant identity in driving the phyllosphere epiphytic and endophytic microbial community structures in mangrove ecosystems.

Sporormielones A-E, bioactive novel C-C coupled orsellinic acid derivative dimers, and their biosynthetic origin.

Sporormielones A-E (1-5), novel C-C coupled orsellinic acid derivative dimers containing tricyclic cores with a dimethylcyclopentenone unit, were obtained, of which 1-3 and 5 showed obvious short-term memory improvement activity in AD flies. Based on transcriptome analysis, 13C labelling, and gene deletion, their plausible biosynthetic mechanism was proposed.

Diversity and community of culturable endophytic fungi from stems and roots of desert halophytes in northwest China.

Halophytes have high species diversity and play important roles in ecosystems. However, endophytic fungi of halophytes in desert ecosystems have been less investigated. In this study, we examined endophytic fungi associated with the stem and root of ten halophytic species colonizing the Gurbantonggut desert. A total of 36 endophytic fungal taxa were obtained, dominated by Alternaria eichhorniae, Monosporascus ibericus, and Pezizomycotina sp.1. The colonization rate and species richness of endophytic fungi varied in the ten plant species, with higher rates in roots than in stems. The endophytic fungal community composition was significantly affected by plant identity and tissue type. Some endophytic fungi showed significant host and tissue preferences. This finding suggests that host identity and tissue type structure endophytic fungal community in a desert ecosystem.

Convergent Estimation Mechanism Design for Nonlinear Fuzzy Systems With Faults.

The convergent estimation for a class of nonlinear Takagi-Sugeno fuzzy systems is concerned, where time-varying process faults and input disturbances are both involved. A convergent estimation mechanism (CEM) based on a set of fuzzy iterative estimation observers is constructed for the nonlinear fuzzy system; meanwhile, the convergence of the mean sequence of estimation errors (for both states and faults) to zero (vector) is proved. However, in the existing literature, the estimation errors can only be proved to be uniformly ultimately bounded when the fault is time varying. In the design procedure, the disturbances on systems in consideration can be isolated effectively in the obtained fuzzy iterative error dynamics through introducing a suitable isolation technique. Numerical examples give the simulation results to show the effectiveness and merits of the proposed CEM.

Spororrminone A and 2-epi-spororrminone A, two new chromones from an endolichenic fungus Sporormiella irregularis.

Two new chromones, spororrminone A (1, (S)-5-hydroxy-2-methyl-4-oxo-2-((S)-5-oxotetrahydrofuran-2-yl)chroman-7-carboxylic acid) and 2-epi-spororrminone A (2, (R)-5-hydroxy-2-methyl-4-oxo-2-((S)-5-oxotetrahydrofuran-2-yl)chroman-7-carboxylic acid), were isolated from an EtOAc extract of an endolichenic fungal strain Sporormiella irregularis (No. 71-11-4-1). The structures of these compounds were identified by spectroscopic analyses. The absolute configuration of 1 was established by single-crystal X-ray diffraction. Spororrminone A (1) and 2-epi-spororrminone A (2) represent the first examples of 2-(5-oxotetrahydrofuran-2-yl) chromones with 7-carboxylic group.

Biocontrol Potential of Fungal Endophytes against Fusarium oxysporum f. sp. cucumerinum Causing Wilt in Cucumber.

Endophytic fungi have received much attention as plant growth promoters as well as biological control agents against many plant pathogens. In this study, 30 endophytic fungal species, isolated from various plants in China, were evaluated using in vitro dual culture assay against Fusarium oxysporum f. sp. cucumerinum, causing wilt in cucumber. The results of the present study clearly showed that all the 30 endophytic fungal isolates were highly capable of inhibiting the mycelial colony growth of Fusarium oxysporum f. sp. cucumerinum with inhibition % over 66% as compared to control treatments. Among all of them, 5 isolates were highly effective such as, Penicillium sp., Guignardia mangiferae, Hypocrea sp., Neurospora sp., Eupenicillium javanicum, and Lasiodiplodia theobromae, respectively. The Penicillium sp. and Hypocrea sp. were highly effective as compared to other isolates. From in vitro results 10 best isolates were selected for greenhouse studies. The results of the greenhouse studies showed that among all of them 3 endophytic fungal isolates successfully suppressed wilt severity when co-inoculation with pathogen Fusarium. oxysporum f. sp. cucumerinum. The endophytic fungi also enhanced plant growth parameters of the host plants, the antagonistic fungal isolates increased over all plant height, aerial fresh, and dry weight as compared to control.

Late Quaternary climate change explains soil fungal community composition rather than fungal richness in forest ecosystems.

The dramatic climate fluctuations of the late Quaternary have influenced the diversity and composition of macroorganism communities, but how they structure belowground microbial communities is less well known. Fungi constitute an important component of soil microorganism communities. They play an important role in biodiversity maintenance, community assembly, and ecosystem functioning, and differ from many macroorganisms in many traits. Here, we examined soil fungal communities in Chinese temperate, subtropical, and tropic forests using Illumina MiSeq sequencing of the fungal ITS1 region. The relative effect of late Quaternary climate change and contemporary environment (plant, soil, current climate, and geographic distance) on the soil fungal community was analyzed. The richness of the total fungal community, along with saprotrophic, ectomycorrhizal (EM), and pathogenic fungal communities, was influenced primarily by the contemporary environment (plant and/or soil) but not by late Quaternary climate change. Late Quaternary climate change acted in concert with the contemporary environment to shape total, saprotrophic, EM, and pathogenic fungal community compositions and with a stronger effect in temperate forest than in tropic-subtropical forest ecosystems. Some contemporary environmental factors influencing total, saprotrophic, EM, and pathogenic fungal communities in temperate and tropic-subtropical forests were different. We demonstrate that late Quaternary climate change can help to explain current soil fungal community composition and argue that climatic legacies can help to predict soil fungal responses to climate change.

New phthalide derivatives from the Biscogniauxia sp. and their activities.

Five new phthalide derivatives, biscogniphthalides A-D (1, 2, 3a/3b, and 4), were isolated from Biscogniauxia sp. (No. 69-8-7-1), along with one related known phthalide (5). Their structures were determined by comprehensive spectroscopic analyses, chemical derivatization, and quantum chemical ECD calculations. In addition, the anti-acetyl cholinesterase, antimicrobial, and anti-α-glucosidase activities of 1-5 were evaluated.