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Background: Transforming coniferous plantation into broadleaved or mixed broadleaved-coniferous plantations is the tendency of forest management strategies in subtropical China. However, the effects of this conversion on soil phosphorus (P) cycling microbial functional genes are still unknown. Methods: Soil samples were collected from 0-20, 20-40, and 40-60 cm (topsoil, middle layer, and subsoil, respectively) under coniferous Pinus massoniana (PM), broadleaved Erythrophleum fordii (EF), and their mixed (PM/EF) plantation in subtropical China. Used metagenomic sequencing to examine the alterations of relative abundances and molecular ecological network structure of soil P-cycling functional genes after the conversion of plantations. Results: The composition of P-cycling genes in the topsoil of PM stand was significantly different from that of PM/EF and EF stands (p < 0.05), and total phosphorus (TP) was the main factor causing this difference. After transforming PM plantation into EF plantation, the relative abundances of P solubilization and mineralization genes significantly increased in the topsoil and middle layer with the decrease of soil TP content. The abundances of P-starvation response regulation genes also significantly increased in the subsoil (p < 0.05), which may have been influenced by soil organic carbon (SOC). The dominant genes in all soil layers under three plantations were phoR, glpP, gcd, ppk, and ppx. Transforming PM into EF plantation apparently increased gcd abundance in the topsoil (p < 0.05), with TP and NO3--N being the main influencing factors. After transforming PM into PM/EF plantations, the molecular ecological network structure of P-cycling genes was more complex; moreover, the key genes in the network were modified with the transformation of PM plantation. Conclusion: Transforming PM into EF plantation mainly improved the phosphate solubilizing potential of microorganisms at topsoil, while transforming PM into PM/EF plantation may have enhanced structural stability of microbial P-cycling genes react to environmental changes. [ABSTRACT FROM AUTHOR]

Aims: Lakeshore wetlands are global carbon (C) hotspots, but their role in C sequestration has been largely overlooked. The rhizosphere has a complex interaction of microbiota and metabolites, which plays an important role in wetland C cycling. This study aims to understand how the rhizospheric interactions affect harvested aboveground C and soil C of lakeshore wetlands in a subtropical region. Methods: An investigation of five lakeshore reed (Phragmites australis) wetlands at the similar latitudes of the Lower Yangtse Valley in China was carried out to explore the relationship of rhizospheric interactions with harvested aboveground C and soil C. The plant traits and soil physicochemical properties were determined due to their important role in affecting rhizosphere interactions. Results: Plant traits and soil physicochemical properties significantly differed among the sites, while aboveground C fixation did not significantly differ. The soil organic C (SOC) content of the topsoil was accounting for the majority of the soil total C at most sites, except for the wetland at the Yangtze River estuary with higher soil pH and conductivity, whose soil inorganic C (SIC) accounted for almost half. Bacterial community and metabolite composition were significantly partitioned across the region. Structural equation modeling revealed the rhizospheric interactions positively affected aboveground C and SOC, but negatively affected SIC. Their effects on soil C content were stronger than those on aboveground C fixation. Conclusions: The rhizosphere exhibited the direct and indirect effects on harvested aboveground C and soil C by altering microbial community structure and metabolite composition. [ABSTRACT FROM AUTHOR]

Mixing with different broadleaf trees into the monocultures of Cunninghamia lanceolata is widely adopted as an efficient transformation of the pure C. lanceolata forest. However, it is unclear how native broad-leaved trees influence the belowground ecological environment of the pure C. lanceolata culture plantation in nutrient-poor soil of South China. Herein, we aimed to investigate how a long-time mixing with native broadleaf trees shape soil microbial community of the pure C. lanceolata forest across different soil depth (0-20cm and 20-40cm) and to clarify relationships between the modified soil microbial community and those affected soil chemical properties. Using high-throughput sequencing technology, microbial compositions from the mixed C. lanceolata-broadleaf forest and the pure C. lanceolata forest were analyzed. Network analysis was utilized to investigate correlations among microorganisms, and network robustness was assessed by calculating network natural connectivity. Results demonstrated that the content of soil microbial biomass carbon and nitrogen, total phosphorus and pH in mixed forest stand were significantly higher than those in pure forest stand, except for available phosphorus in topsoil (0-20cm). Simultaneously, the mixed C. lanceolata-broadleaf forest has a more homogeneous bacterial and fungal communities across different soil depth compared with the pure C. lanceolata forest, wherein the mixed forest recruited more diverse bacterial community in subsoil (20-40cm) and reduced the diversity of fungal community in topsoil. Meanwhile, the mixed forest showed higher bacterial community stability while the pure forest showed higher fungal community stability. Moreover, bacterial communities showed significant correlations with various soil chemical indicators, whereas fungal communities exhibited correlations with only TP and pH. Therefore, the mixed C. lanceolata-broadleaf forest rely on their recruiting bacterial community to enhance and maintain the higher nutrient status of soil while the pure C. lanceolata forest rely on some specific fungi to satisfy their phosphorus requirement for survive strategy. [ABSTRACT FROM AUTHOR]

Straw is widely incorporated into soil worldwide, but most studies have concentrated on the effects of straw mulching or incorporation with topsoil. To determine the effect of depth of straw incorporation on bacterial and fungal communities, we established a field experiment in a region in Northeast China with Haplic Chernozems using four treatments: conventional tillage (CT, tillage to a depth of 15 cm with no straw incorporation), straw incorporation with conventional tillage (SCT, tillage to a depth of 15 cm), inversion tillage (IT, tillage to a depth of 35 cm) and straw incorporation with inversion tillage (SIT, tillage to a depth of 35 cm). The soils were managed by inversion to a depth of 15 or 35 cm after harvest. The results show that soil organic carbon content was significantly higher and pH and bulk density were significantly lower in the 15–35 cm layer in IT and SIT than CT and SCT. Fungal abundance was higher with straw incorporation, but fungal diversity was lower in the 0–15 cm layer in SCT and SIT than in CT and IT. Path length in the bacterial network was shorter and connectivity was higher in CT + SCT than in IT + SIT, leading to a more complex ecosystem, and the fungal network had opposite patterns. The key taxa in the phylum Actinobacteriota and Ascomycota in the microbial networks changed dramatically at the genus level following inversion tillage with straw amendment, which may increase bacterial network resistance to environmental disturbances and unstable fungal networks, resulting in large changes in the fungal community involved in the decomposition of recalcitrant straw-derived C and the more efficient acquisition of limiting resources. [ABSTRACT FROM AUTHOR]

Background: The rhizosphere microbiome, which is shaped by host genotypes, root exudates, and plant domestication, is crucial for sustaining agricultural plant growth. Despite its importance, how plant domestication builds up specific rhizosphere microbiomes and metabolic functions, as well as the importance of these affected rhizobiomes and relevant root exudates in maintaining plant growth, is not well understood. Here, we firstly investigated the rhizosphere bacterial and fungal communities of domestication and wild accessions of tetraploid wheat using amplicon sequencing (16S and ITS) after 9 years of domestication process at the main production sites in China. We then explored the ecological roles of root exudation in shaping rhizosphere microbiome functions by integrating metagenomics and metabolic genomics approaches. Furthermore, we established evident linkages between root morphology traits and keystone taxa based on microbial culture and plant inoculation experiments. Results: Our results suggested that plant rhizosphere microbiomes were co-shaped by both host genotypes and domestication status. The wheat genomes contributed more variation in the microbial diversity and composition of rhizosphere bacterial communities than fungal communities, whereas plant domestication status exerted much stronger influences on the fungal communities. In terms of microbial interkingdom association networks, domestication destabilized microbial network and depleted the abundance of keystone fungal taxa. Moreover, we found that domestication shifted the rhizosphere microbiome from slow growing and fungi dominated to fast growing and bacteria dominated, thereby resulting in a shift from fungi-dominated membership with enrichment of carbon fixation genes to bacteria-dominated membership with enrichment of carbon degradation genes. Metagenomics analyses further indicated that wild cultivars of wheat possess higher microbial function diversity than domesticated cultivars. Notably, we found that wild cultivar is able to harness rhizosphere microorganism carrying N transformation (i.e., nitrification, denitrification) and P mineralization pathway, whereas rhizobiomes carrying inorganic N fixation, organic N ammonification, and inorganic P solubilization genes are recruited by the releasing of root exudates from domesticated wheat. More importantly, our metabolite-wide association study indicated that the contrasting functional roles of root exudates and the harnessed keystone microbial taxa with different nutrient acquisition strategies jointly determined the aboveground plant phenotypes. Furthermore, we observed that although domesticated and wild wheats recruited distinct microbial taxa and relevant functions, domestication-induced recruitment of keystone taxa led to a consistent growth regulation of root regardless of wheat domestication status. Conclusions: Our results indicate that plant domestication profoundly influences rhizosphere microbiome assembly and metabolic functions and provide evidence that host plants are able to harness a differentiated ecological role of root-associated keystone microbiomes through the release of root exudates to sustain belowground multi-nutrient cycles and plant growth. These findings provide valuable insights into the mechanisms underlying plant-microbiome interactions and how to harness the rhizosphere microbiome for crop improvement in sustainable agriculture. CBzZNC2FEDswGcHctbDosa Video Abstract [ABSTRACT FROM AUTHOR]

The effect of exotic plants on Bacillus diversity in the rhizosphere and the role of Bacilli in exotic or native plant species remain poorly understood. Flaveria bidentis is an invasive grass in China. Setaria viridis is a native grass and occurs in areas invaded by F. bidentis. Our objectives were (i) to examine the differences in the Bacillus communities between F. bidentis and S. viridis rhizospheres soil, and (ii) to compare the effects of Bacilli from F. bidentis and S. viridis rhizospheres on the competitiveness of the invasive species. Flaveria bidentis monoculture, mixture of F. bidentis and S. viridis and S. viridis monoculture were designed in the field experiment. Bacillus diversity in their rhizosphere was analyzed using 16S rRNA. One of the dominant Bacilli in the rhizosphere soil of F. bidentis was selected to test its effect on the competitive growth of F. bidentis in a greenhouse experiment. Bacillus diversity differed in F. bidentis and S. viridis rhizosphere. Brevibacterium frigoritolerans was the dominant Bacilli in the rhizosphere of both F. bidentis and S. viridis ; however, its relative abundance in the F. bidentis rhizosphere was much higher than that in the S. viridis rhizosphere. In addition, B. frigoritolerans in the F. bidentis rhizosphere enhanced the growth of the plant compared with that of S. viridis by improving the nitrogen and phosphorus levels. This study showed that F. bidentis invasion influenced Bacillus communities, especially B. frigoritolerans , which, in turn, facilitated F. bidentis growth by increasing the levels of available nitrogen and phosphorus. [ABSTRACT FROM AUTHOR]

Soil microbial communities are affected by interactions between agricultural management (e.g., fertilizer) and soil compartment, but few studies have considered combinations of these factors. We compared the microbial abundance, diversity and community structure in two fertilizer dose (high vs. low NPK) and soil compartment (rhizosphere vs. bulk soils) under 6-year fertilization regimes in a continuous garlic cropping system in China. The soil contents of NO3– and available K were significantly higher in bulk soil in the high-NPK. The 16S rRNA gene-based bacterial and archaeal abundances were positively affected by both the fertilizer dose and soil compartment, and were higher in the high-NPK fertilization and rhizosphere samples. High-NPK fertilization increased the Shannon index and decreased bacterial and archaeal richness, whereas the evenness was marginally positively affected by both the fertilizer dose and soil compartment. Soil compartment exerted a greater effect on the bacterial and archaeal community structure than did the fertilization dose, as demonstrated by both the nonmetric multidimensional scaling and redundancy analysis results. We found that rhizosphere effects significantly distinguished 12 dominant classes of bacterial and archaeal communities, whereas the fertilizer dose significantly identified four dominant classes. In particular, a Linear Effect Size analysis showed that some taxa, including Alphaproteobacteria, Rhizobiales, Xanthomonadaceae and Flavobacterium, were enriched in the garlic rhizosphere of the high-NPK fertilizer samples. Overall, the fertilizer dose interacted with soil compartment to shape the bacterial and archaeal community composition, abundance, and biodiversity in the garlic rhizosphere. These results provide an important basis for further understanding adaptive garlic-microbe feedback, reframing roots as a significant moderating influence in agricultural management and shaping the microbial community. [ABSTRACT FROM AUTHOR]

Bacteria are the most abundant soil microbes and are sensitive to environmental change, especially soil carbon (C) and nitrogen (N) dynamics. The bacterial diversity of rhizosphere and bulk soils associated with desert plants is not well understood. In this study, we measured the properties of rhizosphere and bulk soils at different depths (0–20, 20–40, 40–60, and 60–80 cm), the diversity of bacterial communities (16S rDNA amplicon sequencing), and their relationships with Anabasis aphylla in the southern margin of the Gurbantunggut Desert, Junggar Basin, China. A total of 11,420 operational taxonomic units (OTUs) were obtained from 40 soil samples, belonging to 641 genera, 269 families, 137 orders, 61 classes, and 44 phyla. There were significant differences in electrical conductivity (EC), available nitrogen (AN), available phosphorus (AP), available potassium (AK), and bacterial diversity. The dominant bacterial communities of the rhizosphere and bulk soils at the phylum level were Actinobacteria, Proteobacteria, and Bacteroidetes. At the genus level, the dominant communities of the rhizosphere and bulk soils were Halomonas and Glycomyces, respectively. At different soil depths, the abundances of bacteria in the soil were 10.2% (0–20 cm) > 8.4% (20–40 cm) > 8.3% (60–80 cm) > 6.2% (40–60 cm). Our results indicate that bacteria in the phyla Actinobacteria and Proteobacteria, as well as the genus Halomonas, are key to the drought and salt tolerance of A. aphylla. [ABSTRACT FROM AUTHOR]

Organic acids are influenced by many factors, such as season variations, water levels, vegetation and others. In the study, the rhizosphere soils of lakeshore plants in Poyang Lake, Chaohu Lake and Wuchang Lake in China were sampled under different water level fluctuations, and the amounts of organic acids were measured. Water level fluctuations affect the temporal and spatial characteristics of rhizosphere organic acids. The annual average of the total amount of organic acids in the rhizosphere soil of lakeshore plants in Wuchang Lake was higher than that in the other lakes. The seasonal variations in the amounts of organic acids were the same in the three lakes. The total amounts of organic acids in the rhizosphere soils at high water level sites were higher than those in the low water level sites of the three lakes. The effects of the interactions of season variations and water level fluctuations on the amount of organic acids in the rhizosphere were significant. The results revealed that the lake types changed in response to anthropogenic influence; Wuchang Lake, as a quasi-natural lake, suffered from much more human pollutants than Chaohu Lake as a reservoir-like lake and Poyang Lake as an intermittent lake. [ABSTRACT FROM AUTHOR]

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Understanding the response of soil properties and bacterial communities in rhizosphere soil to aridity and dune types is fundamental to desertification control. This study investigated soil properties and bacterial communities of both rhizosphere and bulk soils of Caragana microphylla from four sites with different aridity indices, and one site with three different types of dunes. All sites were located in the desert regions of northern China. The results indicated that compared with the bulk soil, the soil nutrient content of rhizosphere, especially the content of total phosphorus, was generally significantly improved in different desertification environments. The bacterial richness and diversity were also higher than those of bulk soil, especially in arid regions and fixed dunes. Firmicutes, Actinobacteria, Proteobacteria, and Acidobacteria were the most dominant phyla in all samples. The regression analyses showed that at different sites, soil total organic C, total N, Na+, and total P played key roles in determining the bacterial community structure while total organic carbon, electronic conductivity, pH and total phosphorus were the dominant factors at the different dunes. The results further revealed that the dominant phyla strongly affected by environmental factors at different sites were Acidobacteria, Gemmatimonadetes, and Actinobacteria among which, Acidobacteria and Gemmatimonadetes were negatively correlated with Na+ content. At different types of dunes, Actinobacteria, Planctomycetes, and Gemmatimonadetes were particularly affected by environmental factors. The increased abundance of Actinobacteria in the rhizosphere soil was mainly caused by the decreased soil pH. [ABSTRACT FROM AUTHOR]

Increasing evidence has confirmed the importance of plant-associated bacteria for plant growth and productivity, and thus it is hypothesized that interactions between bacteria and alien plants might play an important role in plant invasions. However, the diversity of the bacterial communities associated with invasive plants is poorly understood. We therefore investigated the diversity of rhizospheric and endophytic bacteria associated with the invasive annual plant Senecio vulgaris L. (Asteraceae) based on 16S rRNA gene data obtained from 57 samples of four Senecio vulgaris populations in a subtropical mountainous area in central China. Significant differences in diversity were observed between plant compartments. Specifically, the rhizosphere harbored many more bacterial operational taxonomic units and showed higher alpha diversity than the leaf and root endospheres. The relative abundance profiles of the bacterial community composition differed substantially between the compartments and populations, especially at the phylum and family levels. However, the top five phyla (Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, and Acidobacteria) accounted for more than 90% of all the bacterial communities. Moreover, similar endophytic communities with a shared core set of bacteria were observed from different Senecio vulgaris populations. Heavy-metal-resistant, phosphate-solubilizing bacteria (Brevundimonas diminuta), nitrogen-fixing bacteria (Rhizobium leguminosarum), and cold-resistant bacteria (Exiguobacterium sibiricum) were present in the endosphere at relatively high abundance. This study, which reveals the structure of bacterial communities and their putative function in invasive Senecio vulgaris plants, is the first step in investigating the role of plant-bacteria interactions in the invasion of this species in China. [ABSTRACT FROM AUTHOR]

Root exudation stimulates microbial decomposition and enhances nutrient availability to plants. It remains difficult to measure and predict this carbon flux in natural conditions, especially for mature woody plants. Based on a known conceptual framework of root functional traits coordination, we proposed that root functional traits may predict root exudation. We measured root exudation and other seven root morphological/chemical/physiological traits for 18 coexisting woody species in a deciduous-evergreen mixed forest in subtropical China. Root exudation, respiration, diameter and nitrogen (N) concentration all exhibited significant phylogenetic signals. We found that root exudation positively correlated with competitive traits (root respiration, N concentration) and negatively with a conservative trait (root tissue density). Furthermore, these relationships were independent of phylogenetic signals. A principal component analysis showed that root exudation and morphological traits loaded on two perpendicular axes. Root exudation is a competitive trait in a multidimensional fine-root functional coordination. The metabolic dimension on which root exudation loaded was relatively independent of the morphological dimension, indicating that increasing nutrient availability by root exudation might be a complementary strategy for plant nutrient acquisition. The positive relationship between root exudation and root respiration and N concentration is a promising approach for the future prediction of root exudation., (© 2020 The Authors New Phytologist © 2020 New Phytologist Trust.)

Autotoxicity is a widespread phenomenon in nature and is considered to be the main factor affecting new natural recruitment of plant populations, which was proven in many natural populations. Cinnamomum migao H. W. Li is an endemic medicinal woody plant species mainly distributed in Southwestern China and is defined as an endangered species by the Red Paper of Endangered Plants in China. The lack of seedlings is considered a key reason for population degeneration; however, no studies were conducted to explain its causes. C. migao contains substances with high allelopathic potential, such as terpenoids, phenolics, and flavonoids, and has strong allelopathic effects on other species. Therefore, we speculate that one of the reasons for C. migao seedling scarcity in the wild is that it exhibits autotoxic allelopathy. In this study, which was performed from the perspective of autotoxicity, we collected leaves, pericarp, seeds, and branches of the same population; we simulated the effects of decomposition and release of litter from these different anatomical parts of C. migao in the field; and we conducted 210-day control experiments on seedling growth, with different concentration gradients, using associated aqueous extracts. The results showed that the leaf aqueous extract (leafAE) significantly inhibited growth indicators and increased damage of the lipid structure of the cell membrane of seedlings, suggesting that autotoxicity from C. migao is a factor restraining seedling growth. The results of the analyses of soil properties showed that, compared with the other treatments, leafAE treatment inhibited soil enzyme activity and also had an impact on soil fungi. Although leafAE could promote soil fertility to some extent, it did not change the effect of autotoxic substances on seedling growth. We conclude that autotoxicity is the main obstacle inhibiting seedling growth and the factor restraining the natural regeneration of C. migao. [ABSTRACT FROM AUTHOR]