Soil pH: a key edaphic factor regulating distribution and functions of bacterial community along vertical soil profiles in red soil of pomelo orchard.

BACKGROUND: Soil microbes exist throughout the soil profile and those inhabiting topsoil (0-20 cm) are believed to play a key role in nutrients cycling. However, the majority of the soil microbiology studies have exclusively focused on the distribution of soil microbial communities in the topsoil, and it remains poorly understood through the subsurface soil profile (i.e., 20-40 and 40-60 cm). Here, we examined how the bacterial community composition and functional diversity changes under intensive fertilization across vertical soil profiles [(0-20 cm (RS1), 20-40 cm (RS2), and 40-60 cm (RS3)] in the red soil of pomelo orchard, Pinghe County, Fujian, China. RESULTS: Bacterial community composition was determined by 16S rRNA gene sequencing and interlinked with edaphic factors, including soil pH, available phosphorous (AP), available nitrogen (AN), and available potassium (AK) to investigate the key edaphic factors that shape the soil bacterial community along with different soil profiles. The most dominant bacterial taxa were Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, Crenarchaeota, and Bacteriodetes. Bacterial richness and diversity was highest in RS1 and declined with increasing soil depth. The distinct distribution patterns of the bacterial community were found across the different soil profiles. Besides, soil pH exhibited a strong influence (pH ˃AP ˃AN) on the bacterial communities under all soil depths. The relative abundance of Proteobacteria, Actinobacteria, Crenarchaeota, and Firmicutes was negatively correlated with soil pH, while Acidobacteria, Chloroflexi, Bacteriodetes, Planctomycetes, and Gemmatimonadetes were positively correlated with soil pH. Co-occurrence network analysis revealed that network topological features were weakened with increasing soil depth, indicating a more stable bacterial community in the RS1. Bacterial functions were estimated using FAPROTAX and the relative abundance of functional bacterial community related to metabolic processes, including C-cycle, N-cycle, and energy production was significantly higher in RS1 compared to RS2 and RS3, and soil pH had a significant effect on these functional microbes. CONCLUSIONS: This study provided the valuable findings regarding the structure and functions of bacterial communities in red soil of pomelo orchards, and highlighted the importance of soil depth and pH in shaping the soil bacterial population, their spatial distribution and ecological functioning. These results suggest the alleviation of soil acidification by adopting integrated management practices to preserve the soil microbial communities for better ecological functioning.

Ecological consequence of nomad settlement policy in the pasture area of Qinghai-Tibetan Plateau: From plant and soil perspectives.

The prevailing trend in pasture areas worldwide is that of mobile pastoralism to settlement, which produces a positive impact on pastoral livelihoods and livestock husbandry. However, the impact of nomad settlement on the grassland ecosystem is not well documented and remains debatable. In response, from 2001 to 2015, the central Chinese government initiated the Nomad Settlement Policy (NSP). In this study, we conducted a case study of the pastoral area of the Qinghai-Tibetan Plateau, to investigate impact of NSP on grassland ecological conditions including plants, soil and microorganisms. Results showed that grassland ecological conditions presented differentiation characteristics, with changes depending on the distance from settlements. The grassland ecological conditions showed heavy degradation near the settlement based on the classification of Qinghai-Tibetan Plateau grassland degradation, and gradual improvement with increasing distance from the settlement. Based on our investigation and previous studies, we found that intervention of NSP decreased the distance in livestock mobility and led to intensive grazing near the settlement, thereby increased grassland degradation. At the same time, the grassland maintained a relatively good ecological condition with the increase in distance from settlement, which may be attributed to short-period grazing and light trampling effects. Our findings provide new insight into the grassland ecological condition in the aftermath of NSP implementation, and also put forward some measures (e.g. multi-household grazing management, pastoral cooperative) to restore the grassland degradation.

Visible-light-induced radical trifluoromethylthiolation of N-(o-cyanobiaryl)acrylamides.

An efficient and general visible-light-mediated trifluoromethylthiolation of N-(o-cyanobiaryl)acrylamides has been successfully accomplished using N-trifluoromethylthiosaccharin as an effective source of SCF3 radicals. The reaction was proposed to proceed via a domino radical trifluoromethylthiolation/cyano insertion/cyclization to afford the corresponding SCF3-containing ring-fused phenanthridine derivatives in moderate to good yields.

Visible-light-mediated direct difluoromethylation of alkynoates: synthesis of 3-difluoromethylated coumarins.

A photoredox-catalyzed direct difluoromethylation of alkynoates has been developed. A well-designed photoredox system induces a single-step, regioselective installation of CF2H onto alkynes. Difluoromethyl sulfone was used as an easy to handle CF2H radical source to afford the desired 3-difluoromethylated coumarins in moderate to good yields via a radical-triggered tandem difluoromethylation/5-exo cyclization/ester migration process.

Regioselective 2,2,2-Trifluoroethylation of Imidazopyridines by Visible Light Photoredox Catalysis.

A visible-light-induced C-3 selective trifluoroethylation of imidazoheterocycles using 1,1,1-trifluoro-2-iodoethane as trifluoroethyl radical sources was developed. The methodology enables the introduction of a trifluoroethyl group in a fast and efficient reaction under mild conditions with excellent regioselectivities and high functional group tolerance.

Synthesis, Structure, and Photophysical Properties of Two Four-Coordinate Cu(I)-NHC Complexes with Efficient Delayed Fluorescence.

Two luminescent cationic heteroleptic four-coordinate Cu(I) complexes supported by N-heterocyclic carbene ligand and diphosphine ligand were successfully prepared and characterized. These complexes adopt typical distorted tetrahedral configuration and have high stability in solid state. Quantum chemical calculations show carbene units have contributions to both highest occupied molecular orbitals and lowest unoccupied molecular orbitals of these Cu(I)-NHC complexes, the lowest-lying singlet and triplet excitations (S0 → S1 and S0 → T1) of [Cu(Pyim)(POP)](PF6) are dominated by metal-to-ligand charge transfer (MLCT) transition, while the S0 → S1 and S0 → T1 excitations of [Cu(Qbim)(POP)](PF6) are mainly MLCT and ligand-centered transitions, respectively. These Cu(I)-NHC complexes show efficient long-lifetime emissions (λem = 520 nm, τ = 79.8 µs, Φ = 0.56 for [Cu(Pyim)(POP)](PF6), λem = 570 nm, τ = 31.97 µs (78.99%) and 252.2 µs (21.01%), Φ = 0.35 for [Cu(Qbim)(POP)](PF6)) in solid state at room temperature, which are confirmed as delayed fluorescence by investigating the emissions at 77 K.

Shading decreases plant carbon preferential allocation towards the most beneficial mycorrhizal mutualist.

Preferential allocation towards the most beneficial mutualist could maintain mycorrhizal mutualism. Context dependence of preferential allocation could then determine environmental patterns in abundance of mycorrhizal mutualists. We assessed the preferential allocation of carbon (C) and differential phosphorus (P) uptake across four light treatments between the host plant Allium vineale and two arbuscular mycorrhizal (AM) fungi within a split-root system. The ratios of C allocation and P uptake between the beneficial and nonbeneficial AM fungi were measured using isotopic labelling. Allium vineale preferentially allocated more C towards roots infected with the most beneficial AM fungus in high light and, in return, received more P from the beneficial fungus. Preferential allocation declined with shading, as A. vineale allocated 25% of labelled C to roots infected with beneficial AM fungi in high light, but only 15% with shading, a similar percentage to that allocated to roots infected with nonbeneficial fungi regardless of shading. Our findings demonstrate that plant preferential allocation towards the most beneficial mycorrhizal mutualist depends upon above-ground resources, suggesting that the abundance of beneficial mycorrhizal fungi will increase with amount of above-ground resources, with implications for mycorrhizal mediation of plant productivity with anthropogenic change.

Visible-light-mediated radical aryldifluoroacetylation of alkynes with ethyl bromodifluoroacetate for the synthesis of 3-difluoroacetylated coumarins.

A mild and efficient method for the synthesis of 3-difluoroacetylated coumarins through visible-light-promoted aryldifluoroacetylation of alkynes with ethyl bromodifluoroacetate has been developed. The reaction allows the direct formation of Csp(2)-CF2COOEt and C-C bonds via a proposed tandem radical cyclization process.

Aerobic oxidation of alcohols and the synthesis of benzoxazoles catalyzed by a cuprocupric coordination polymer (Cu(+)-CP) assisted by TEMPO.

A Cu(+)-CP based on the tetranuclear unit {[(HSQPA)2Cu4(bipy)4]·2H2O}n·2nH2O has been constructed through Cu(2+) salt, 2-(sulfonylquinlium-8-yloxy)phthalic acid (H3SQPA), and 4,4'-bipyridine (bipy). This Cu(+)-CP combined with 2,2,6,6-tetramethylpiperidine-1-oxyl as the cocatalyst is an effective catalyst for aerobic oxidation of alcohols and the synthesis of benzoxazoles and can be recycled at least four times without losing its catalytic activity.

N-Heterocyclic carbene (NHC)-modulated Pd/Cu cocatalyzed three-component synthesis of 2,6-diarylquinolines.

Two new NHC adducts of cyclopalladated ferrocenylpyrazine complexes 1-2 have been prepared and characterized. An efficient NHC-modulated Pd/Cu cocatalyzed three-component coupling reaction for the synthesis of 2,6-diarylquinolines from aminobenzyl alcohols, aryl ketones, and arylboronic acids in air is described. The reaction involves oxidation, cyclization and Suzuki reactions. The luminescence of the resulting arylquinolines 3-30 was also investigated.

Spatial distribution and drivers of arbuscular mycorrhizal fungi on the Tibetan Plateau.

Introduction: Arbuscular mycorrhizal fungi (AMF) are pivotal in plant resource acquisition, mediating plant interactions, and influencing soil carbon dynamics. However, their biogeographical distribution in Tibetan alpine grasslands remains understudied. Methods: In this research, we examined the distribution pattern of AMF communities and their key determinants along a 2000-km transect across the Tibetan plateau, encompassing 7 alpine meadows and 8 alpine steppes. Results: Our findings indicate that AMF community diversity and composition exhibit similarities between alpine meadows and alpine steppes, primarily influenced by latitude and evapotranspiration. At the genus level, Glomus predominated in both alpine meadow (36.49%±2.67%) and alpine steppe (41.87%±2.36%) soils, followed by Paraglomus (27.14%±3.69%, 32.34%±3.28%). Furthermore, a significant decay relationship of AMF community was observed over geographical distance. Null model analyses revealed that random processes predominantly (>50%) drove the assembly of AMF communities. Discussion: In summary, our study elucidates the spatial distribution pattern of AMF in Tibetan plateau grasslands and underscores the significant influence of geographical and climatic factors on AMF community dynamics.

Unraveling two decades of phyllosphere endophytes: tracing research trends and insights through visualized knowledge maps, with emphasis on microbial interactions as emerging frontiers.

Phyllosphere endophytes play a critical role in a myriad of biological functions, such as maintaining plant health and overall fitness. They play a determinative role in crop yield and quality by regulating vital processes, such as leaf functionality and longevity, seed mass, apical growth, flowering, and fruit development. This study conducted a comprehensive bibliometric analysis aiming to review the prevailing research trajectories in phyllosphere endophytes and harness both primary areas of interest and emerging challenges. A total of 156 research articles on phyllosphere endophytes, published between 2002 and 2022, were retrieved from the Web of Science Core Collection (WoSCC). A systematic analysis was conducted using CiteSpace to visualize the evolution of publication frequency, the collaboration network, the co-citation network, and keywords co-occurrence. The findings indicated that initially, there were few publications on the topic of phyllosphere endophytes. However, from 2011 onwards, there was a notable increase in the number of publications on phyllosphere endophytes, gaining worldwide attention. Among authors, Arnold, A Elizabeth is widely recognized as a leading author in this research area. In terms of countries, the USA and China hold the highest rankings. As for institutional ranking, the University of Arizona is the most prevalent and leading institute in this particular subject. Collaborative efforts among the authors and institutions tend to be confined to small groups, and a large-scale collaborative network needs to be established. This study identified the influential journals, literature, and hot research topics. These findings also highlight the interconnected nature of key themes, e.g., phyllosphere endophyte research revolves around the four pillars: diversity, fungal endophytes, growth, and endophytic fungi. This study provides an in-depth perspective on phyllosphere endophytes studies, revealing the identification of biodiversity and microbial interaction of phyllosphere endophytes as the principal research frontiers. These analytical findings not only elucidate the recent trajectory of phyllosphere endophyte research but also provide invaluable insights for similar studies and their potential applications on a global scale.

Patterns of diversity and adaptation in Glomeromycota from three prairie grasslands.

Arbuscular mycorrhizal (AM) fungi are widespread root symbionts that often improve the fitness of their plant hosts. We tested whether local adaptation in mycorrhizal symbioses would shape the community structure of these root symbionts in a way that maximizes their symbiotic functioning. We grew a native prairie grass (Andropogon gerardii) with all possible combinations of soils and AM fungal inocula from three different prairies that varied in soil characteristics and disturbance history (two native prairie remnants and one recently restored). We identified the AM fungi colonizing A. gerardii roots using PCR amplification and cloning of the small subunit rRNA gene. We observed 13 operational taxonomic units (OTUs) belonging to six genera in three families. Taxonomic richness was higher in the restored than the native prairies with one member of the Gigaspora dominating the roots of plants grown with inocula from native prairies. Inoculum source and the soil environment influenced the composition of AM fungi that colonized plant roots. Correspondingly, host plants and AM fungi responded significantly to the soil-inoculum combinations such that home fungi often had the highest fitness and provided the greatest benefit to A. gerardii. Similar patterns were observed within the soil-inoculum combinations originating from two native prairies, where five sequence types of a single Gigaspora OTU were virtually the only root colonizers. Our results indicate that indigenous assemblages of AM fungi were adapted to the local soil environment and that this process occurred both at a community scale and at the scale of fungal sequence types within a dominant OTU.

One-pot synthesis of ferrocenyl ketones containing biaryls and 6-aryl-2-ferrocenylquinolines via Ir/Pd-cocatalyzed α-alkylation/Suzuki reaction.

An efficient PPh3-cyclometalated iridium(III) benzo[h]quinoline hydride 1/Pd(OAc)2-cocatalyzed three-component α-alkylation/Suzuki reaction has been developed. The three-component reaction of 4-bromobenzyl alcohol, acetylferrocene, and arylboronic acids gives ferrocenyl ketones containing biaryls in moderate to good yields. This method was successfully applied to a one-pot synthesis of 6-aryl-2-ferrocenyl quinolines, using (2-amino-5-bromophenyl)methanol instead of 4-bromobenzyl alcohol.

Aerobic C-C Bond Cleavage of Allylic Alcohols via Co-Catalyzed Hydrogen Atom Transfer.

A simple, efficient method has been developed for the CoIII-H-catalyzed aerobic C-C bond cleavage of tertiary allylic alcohols to access ketones. This novel approach presents excellent chemoselectivity, good functional group compatibility, and high yields. This reaction occurs through a HAT-initiated peroxide intermediate, and an adjacent glycol-type diradical fragmentation process is recommended.

Iridium Catalysts with f-Amphbinol Ligands: Highly Stereoselective Hydrogenation of a Variety of Ketones.

A series of novel and modular ferrorence-based amino-phosphine-binol (f-amphbinol) ligands have been successfully synthesized. The f-amphbinol ligands exhibited extremely high air stability and catalytic efficiency in the Ir-catalyzed stereoselective hydrogenation of various ketones to afford corresponding stereodefined alcohols with excellent results (full conversions, cis/trans >99:1, and 83% → 99% ee, TON up to 500 000). Control experiments have shown that -OH and -NH groups played a key role in this stereoselective hydrogenation.

Long-term fencing can't benefit plant and microbial network stability of alpine meadow and alpine steppe in Three-River-Source National Park.

A great number of fencing facilities has been established in Three-River-Source National Park. However, with the transformation of wild animals into the main consumers of grassland ecosystem and the increasing years of fence (>15 years), whether the fence still has a positive effect on grassland ecosystem has become controversial. Therefore, taking the alpine steppe and alpine meadow in Three-River-Source National Park as the case study, this study focused on the effects of long-term enclosure on different ecological components by investigating plant communities, soil physical and chemical characteristics and soil microbial characteristics (16S, ITS). Furthermore, we evaluated the ecological benefits of long-term fencing based on the stability of plant communities and microbial networks. We found that fencing did not significantly promote the stability of plant community in different grassland types. The analysis of bacteria-fungal symbiotic network indicated that fencing significantly reduced the stability of soil microbial network in alpine meadows. The results of structural equation showed that the microbial community was indirectly affected by the changes of soil moisture content (SMC) and soil total nutrient content in the alpine steppe, and the stability of microbial network was significantly correlated with the diversity of fungal community. In alpine meadows, fencing indirectly affected soil microbial community by changing SMC and pH. High SMC was not conducive to microbial network stability, while high plant community stability was beneficial to microbial network stability. Network stability was remarkably related to bacterial community composition and diversity, as well as fungal community diversity. Therefore, in Three-River-Source National Park, the positive effects of long-term fencing on various components in different grassland types are weak, especially the negative effects on the stability of soil microbial community in alpine meadows may also weaken the stability of the ecosystem, which is not conducive to the ecological protection of grassland ecosystem.

Recovery through proper grazing exclusion promotes the carbon cycle and increases carbon sequestration in semiarid steppe.

Grazing exclusion changes soil physical-chemical characteristics, rapidly affects microbial community composition and function, and alters biogeochemical processes, e.g., carbon (C) cycle, over time. However, the temporal dynamics of CO2 emission and CH4 uptake during grassland restoration chronosequences remain poorly understood. We investigated soil CO2 emission and CH4 uptake, the genes related to CO2 and CH4 production and reduction (cbbL, cbbM, chiA, and pmoA), and associated microbial communities under different durations of grazing exclusion (0, 7, 16, 25, and 38 years) to reveal the mechanisms and potential of soil CO2 emission and CH4 uptake in a semi-arid steppe. The results showed that a proper exclusion period could significantly improve soil physical-chemical conditions, vegetation community, and soil C-cycling. The abundance of C-cycling functional genes (cbbL, cbbM, chiA and pmoA), CH4 uptake and CO2 emission rates showed a single-peak pattern with increasing duration of grazing exclusion, peaking at 16 years and then decreasing in the period between 25 and 38 years, indicating that the effect of exclusion weakened when the exclusion period was too long. The changes in C-cycling functional genes and microbial communities are primarily influenced by aboveground net primary productivity (ANPP), and are associated with CO2, CH4, soil water content (SWC), and soil organic carbon (SOC). Structural equation modeling showed that increases in SOC content and pmoA abundance caused by an increase in ANPP accelerated CO2 emission and CH4 uptake rates, respectively. Our results provide valuable insights into the critical role of grazing exclusion in promoting grassland restoration and carbon sequestration, and have potential implications for sustainable land management practices.

Vegetation structural shift tells environmental changes on the Tibetan Plateau over 40 years.

Structural information of grassland changes on the Tibetan Plateau is essential for understanding alterations in critical ecosystem functioning and their underlying drivers that may reflect environmental changes. However, such information at the regional scale is still lacking due to methodological limitations. Beyond remote sensing indicators only recognizing vegetation productivity, we utilized multivariate data fusion and deep learning to characterize formation-based plant community structure in alpine grasslands at the regional scale of the Tibetan Plateau for the first time and compared it with the earlier version of Vegetation Map of China for historical changes. Over the past 40 years, we revealed that (1) the proportion of alpine meadows in alpine grasslands increased from 50% to 69%, well-reflecting the warming and wetting trend; (2) dominances of Kobresia pygmaea and Stipa purpurea formations in alpine meadows and steppes were strengthened to 76% and 92%, respectively; (3) the climate factor mainly drove the distribution of Stipa purpurea formation, but not the recent distribution of Kobresia pygmaea formation that was likely shaped by human activities. Therefore, the underlying mechanisms of grassland changes over the past 40 years were considered to be formation dependent. Overall, the first exploration for structural information of plant community changes in this study not only provides a new perspective to understand drivers of grassland changes and their spatial heterogeneity at the regional scale of the Tibetan Plateau, but also innovates large-scale vegetation study paradigm.

Structural competition between halogen bonds and lone-pair···π interactions in solution.

Structural competition between halogen bonds and lone-pair···π interactions in solution is studied using (13)C NMR combined with density functional theory calculations. Among the halogen bonds considered, only the iodine bonds and a few bromine bonds are strong enough to compete successfully with the lone-pair···π interactions.