Differential response of bacterial diversity and community composition to different tree ages of pomelo under red and paddy soils

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.

Metagenomics-based exploration of key soil microorganisms contributing to continuously planted Casuarina equisetifolia growth inhibition and their interactions with soil nutrient transformation

Casuarina equisetifolia (C. equisetifolia) is an economically important forest tree species, often cultivated in continuous monoculture as a coastal protection forest. Continuous planting has gradually affected growth and severely restricted the sustainable development of the C. equisetifolia industry. In this study, we analyzed the effects of continuous planting on C. equisetifolia growth and explored the rhizosphere soil microecological mechanism from a metagenomic perspective. The results showed that continuous planting resulted in dwarfing, shorter root length, and reduced C. equisetifolia seedling root system. Metagenomics analysis showed that 10 key characteristic microorganisms, mainly Actinoallomurus, Actinomadura, and Mycobacterium, were responsible for continuously planted C. equisetifolia trees. Quantitative analysis showed that the number of microorganisms in these three genera decreased significantly with the increase of continuous planting. Gene function analysis showed that continuous planting led to the weakening of the environmental information processing-signal transduction ability of soil characteristic microorganisms, and the decrease of C. equisetifolia trees against stress. Reduced capacity for metabolism, genetic information processing-replication and repair resulted in reduced microbial propagation and reduced microbial quantity in the rhizosphere soil of C. equisetifolia trees. Secondly, amino acid metabolism, carbohydrate metabolism, glycan biosynthesis and metabolism, lipid metabolism, metabolism of cofactors and vitamins were all significantly reduced, resulting in a decrease in the ability of the soil to synthesize and metabolize carbon and nitrogen. These reduced capacities further led to reduced soil microbial quantity, microbial carbon and nitrogen, microbial respiration intensity, reduced soil enzyme nutrient cycling and resistance-related enzyme activities, a significant reduction in available nutrient content of rhizosphere soils, a reduction in the ion exchange capacity, and an impediment to C. equisetifolia growth. This study provides an important basis for the management of continuously planted C. equisetifolia plantations.

Differential response of the soil nutrients, soil bacterial community structure and metabolic functions to different risk areas in Lead-Zine tailings

Rapid growth in the mining industry has brought about a large formation of tailings, which result in serious destruction of the ecological environment and severe soil pollution problems. This study assesses soil nutrients, soil bacterial community and soil microbes' metabolic function in heavily polluted areas (W1), moderately polluted areas (W2), lightly polluted areas (W3) and clean areas (CK) using 16S Illumina sequencing. The results of this study showed that compared with CK, a severe loss of soil nutrients and richness of OTUs (Chao1 and ACE indices) were observed with the aggravated pollution of tailings. The Chao1 and ACE indices in the W1 group decreased significantly by 15.53 and 16.03%, respectively, (p < 0.01). Besides, the relative abundance of Actinobacteria and Proteobacteria was high whereas and relative abundance of Chloroflexi in the polluted areas. Among them, W1 groups increased significantly the relative abundance of Actinobacteria and decreased significantly the relative abundance of Chloroflexi, these can be used as indicator phyla for changes in soil community structures under polluted stress. Tax4 Fun analysis showed that W1 groups affected the soil bacterial community and altered the primary types of biological metabolism in polluted areas. Tailings have adverse impacts on soil bacterial community and metabolic functions, and the deterioration in soil quality is dependent on the levels of tailings pollution. Cumulatively, this study provides valuable information on the bacterial community structure and metabolic functions in the tailing polluted soil.

Differences in Juniperus przewalskii Rhizosphere Microbiomes across Age Classes: Community Diversity and Assembly

Evidence shows that biotic and abiotic factors have apparent diversity at different forest ages, leading to changes in rhizosphere microbiomes. However, the difference in diversity, co-occurrence pattern, and assembly of the rhizosphere microbial community among the different forest ages is still unclear. A total of 24 Juniperus przewalskii rhizosphere soil samples were selected from four representative age classes, using diameter at breast height (DBH) as a proxy for tree age (age class I: 5 < DBH ≤ 12.5 cm, age class II: 12.5 < DBH ≤ 22.5 cm, age class III: 22.5 < DBH ≤ 32.5 cm, and age class IV: DBH > 32.5 cm), and analyzed the structural characteristics of the soil microbial community by high-throughput amplicon sequencing. With the increase in age class, the microbial community α-diversity and β-diversity had an increased trend. The bacterial Shannon index in class II and class III were markedly higher than in class I. From class I to class IV, the relative abundances of dominant phyla such as Actinobacteria and Ascomycota decreased, and the relative abundances of Proteobacteria and Basidiomycota increased in contrast. The complexity and association stability of the bacteria and fungi community network structure increase with forest age. Stochastic processes mediated the assembly of soil bacterial communities, while deterministic processes played a more significant role in the assembly of fungal communities. In addition, the relative importance of deterministic components in the microbial community increased significantly with age class. Random forests suggested that soil pH, plant Shannon-Wiener index (H), and Pielou's evenness index (J) were the most important driving factors of bacterial and fungal community assembly. Overall, these results provide information useful for understanding the generation and maintenance mechanisms of rhizosphere microbial communities across age classes.