Fighting climate change: soil bacteria communities and topography play a role in plant colonization of desert areas

Analysis of Volatile Compounds in Citri grandis from Different Regions in South China and the Response of Volatile Compounds to Ecological Factors

Citri grandis Exocarpium (Chinese name Huajuhong, HJH) is a traditional Chinese medicinal herb widely used in traditional medicines and foods in China due to its efficacy in treating coughs and excessive phlegm. This study employed HS-SPME-GC-MS to analyze the volatile compounds in HJH samples from different regions, with the aim of distinguishing samples from Huazhou from those of other origins and exploring their potential relationship with ecological factors. A multidimensional strategy was utilized to analyze the relationships between volatile oils, climatic factors, and soil elements, examining how volatile compounds responded to ecological factors. From 47 batches of HJH samples across various regions, eight significantly different volatile compounds were identified, serving as chemical markers for HJH from Huazhou. The findings elucidate the impact of ecological factors on the volatile compounds of HJH, highlighting environmental factors relating to the authenticity of HJH from Huazhou. The results indicate that the authenticity of HJH is shaped by the unique climatic and soil environments of Huazhou.

Leaf Health Status Regulates Endophytic Microbial Community Structure, Network Complexity, and Assembly Processes in the Leaves of the Rare and Endangered Plant Species Abies fanjingshanensis

The rare and endangered plant species Abies fanjingshanensis, which has a limited habitat, a limited distribution area, and a small population, is under severe threat, particularly due to poor leaf health. The plant endophytic microbiome is an integral part of the host, and increasing evidence indicates that the interplay between plants and endophytic microbes is a key determinant for sustaining plant fitness. However, little attention has been given to the differences in the endophytic microbial community structure, network complexity, and assembly processes in leaves with different leaf health statuses. Here, we investigated the endophytic bacterial and fungal communities in healthy leaves (HLs) and non-healthy leaves (NLs) of A. fanjingshanensis using 16S rRNA gene and internal transcribed spacer sequencing and evaluated how leaf health status affects the co-occurrence patterns and assembly processes of leaf endophytic microbial communities based on the co-occurrence networks, the niche breadth index, a neutral community model, and C-score metrics. HLs had significantly greater endophytic bacterial and fungal abundance and diversity than NLs, and there were significant differences in the endophytic microbial communities between HLs and NLs. Leaf-health-sensitive endophytic microbes were taxonomically diverse and were mainly grouped into four ecological clusters according to leaf health status. Poor leaf health reduced the complexity of the endophytic bacterial and fungal community networks, as reflected by a decrease in network nodes and edges and an increase in degrees of betweenness and assortativity. The stochastic processes of endophytic bacterial and fungal community assembly were weakened, and the deterministic processes became more important with declining leaf health. These results have important implications for understanding the ecological patterns and interactions of endophytic microbial communities in response to changing leaf health status and provide opportunities for further studies on exploiting plant endophytic microbes to conserve this endangered Abies species.

From guest to host: parasite Cistanche deserticola shapes and dominates bacterial and fungal community structure and network complexity

BACKGROUND

Rhizosphere and plant microbiota are assumed to play an essential role in deciding the well-being of hosts, but effects of parasites on their host microbiota have been rarely studied. Also, the characteristics of the rhizosphere and root microbiota of parasites and hosts under parasitism is relatively unknown. In this study, we used Cistanche deserticola and Haloxylon ammodendron from cultivated populations as our model parasites and host plants, respectively. We collected samples from BULK soil (BULK), rhizosphere soil of H. ammodendron not parasitized (NCD) and parasitized (RHA) to study how the parasite influenced the rhizosphere microbiota of the host. We also collected samples from the rhizosphere soil and roots of C. deserticola (RCD and ECD) and Haloxylon ammodendron (RHA and EHA) to explore the difference between the microbiota of the parasite and its host under parasitism.

RESULTS

The parasite reduced the compositional and co-occurrence network complexities of bacterial and fungal microbiota of RHA. Additionally, the parasite increased the proportion of stochastic processes mainly belonging to dispersal limitation in the bacterial microbiota of RHA. Based on the PCoA ordinations and permutational multivariate analysis of variance, the dissimilarity between microbiota of C. deserticola and H. ammodendron were rarely evident (bacteria, R² = 0.29971; fungi, R² = 0.15631). Interestingly, four hub nodes of H. ammodendron in endosphere fungal microbiota were identified, while one hub node of C. deserticola in endosphere fungal microbiota was identified. It indicated that H. ammodendron played a predominant role in the co-occurrence network of endosphere fungal microbiota. Source model of plant microbiome suggested the potential source percentage from the parasite to the host (bacteria: 52.1%; fungi: 16.7%) was lower than host-to-parasite (bacteria: 76.5%; fungi: 34.3%), illustrating that microbial communication was bidirectional, mainly from the host to the parasite.

CONCLUSIONS

Collectively, our results suggested that the parasite C. deserticola shaped the diversity, composition, co-occurrence network, and community assembly mechanisms of the rhizosphere microbiota of H. ammodendron. Additionally, the microbiota of C. deserticola and H. ammodendron were highly similar and shared. Our findings on parasite and host microbiota provided a novel line of evidence supporting the influence of parasites on the microbiota of their hosts.

Increasing precipitation weakened the negative effects of simulated warming on soil microbial community composition in a semi-arid sandy grassland

Soil microbial diversity, composition, and function are sensitive to global change factors. It has been predicted that the temperature and precipitation will increase in northern China. Although many studies have been carried out to reveal how global change factors affect soil microbial biomass and composition in terrestrial ecosystems, it is still unexplored how soil microbial diversity and composition, especially in microbial functional genes, respond to increasing precipitation and warming in a semiarid grassland of northern China. A field experiment was established to simulate warming and increasing precipitation in a temperate semiarid grassland of the Horqin region. Soil bacterial (16S) and fungal (ITS1) diversity, composition, and functional genes were analyzed after two growing seasons. The result showed that warming exerted negative effects on soil microbial diversity, composition, and predicted functional genes associated with carbon and nitrogen cycles. Increasing precipitation did not change soil microbial diversity, but it weakened the negative effects of simulated warming on soil microbial diversity. Bacterial and fungal diversities respond consistently to the global change scenario in semiarid sandy grassland, but the reasons were different for bacteria and fungi. The co-occurrence of warming and increasing precipitation will alleviate the negative effects of global change on biodiversity loss and ecosystem degradation under a predicted climate change scenario in a semiarid grassland. Our results provide evidence that soil microbial diversity, composition, and function changed under climate change conditions, and it will improve the predictive models of the ecological changes of temperate grassland in future climate change scenarios.

Environmental Response to Root Secondary Metabolite Accumulation in Paeonia lactiflora: Insights from Rhizosphere Metabolism and Root-Associated Microbial Communities

Paeonia lactiflora is a commercial crop with horticultural and medicinal value. Although interactions between plants and microbes are increasingly evident and considered to be drivers of ecosystem service, the regulatory relationship between microbial communities and the growth and root metabolites of P. lactiflora is less well known. Here, soil metabolomics indicated that carbohydrates and organic acids were enriched in the rhizosphere (RS) with higher diversity. Moreover, the variation of root-associated microbiotas between the bulk soil (BS) and the RS of P. lactiflora was investigated via 16S rRNA and internally transcribed spacer (ITS) amplicon sequencing. The RS displayed a low-diversity community dominated by copiotrophs, whereas the BS showed an oligotroph-dominated, high-diversity community. Hierarchical partitioning showed that cation exchange capacity (CEC) was the main factor affecting microbial community diversity. The null model and the dispersion niche continuum index (DNCI) suggested that stochastic processes (dispersal limitation) dominated the community assembly of both the RS and BS. The bacterial-fungal interkingdom networks illustrated that the RS possessed more complex and stable co-occurrence patterns. Meanwhile, positive link numbers and positive cohesion results revealed more cooperative relationships among microbes in the RS. Additionally, random forest model prediction and two partial least-squares path model (PLS-PM) analyses showed that the P. lactiflora root secondary metabolites were comprehensively impacted by soil water content (SWC), mean annual precipitation (MAP), pH (abiotic), and Alternaria (biotic). Collectively, this study provides a theoretical basis for screening the microbiome associated with the active components of P. lactiflora. IMPORTANCE Determining the taxonomic and functional components of the rhizosphere microbiome, as well as how they differ from those of the bulk soil microbiome, is critical for manipulating them to improve plant growth performance and increase agricultural yields. Soil metabolic profiles can help enhance the understanding of rhizosphere exudates. Here, we explored the regulatory relationship across environmental variables (root-associated microbial communities and soil metabolism) in the accumulation of secondary metabolites of P. lactiflora. Overall, this work improves our knowledge of how the rhizosphere affects soil and microbial communities. These observations improve the understanding of plant-microbiome interactions and introduce new horizons for synthetic community investigations as well as the creation of microbiome technologies for agricultural sustainability.

Structural mutations of small single copy (SSC) region in the plastid genomes of five Cistanche species and inter-species identification

BACKGROUND

Cistanche is an important genus of Orobanchaceae, with critical medicinal, economic, and desertification control values. However, the phylogenetic relationships of Cistanche genus remained obscure. To date, no effective molecular markers have been reported to discriminate effectively the Cistanche closely related species reported here. In this study, we obtained and characterized the plastomes of four Cistanche species from China, to clarify the phylogenetic relationship within the genus, and to develop molecular markers for species discrimination.  RESULTS: Four Cistanche species (Cistanche deserticola, Cistanche salsa, Cistanche tubulosa and Cistanche sinensis), were deep-sequenced with Illumina. Their plastomes were assembled using SPAdes and annotated using CPGAVAS2. The plastic genomes were analyzed in detail, finding that all showed the conserved quadripartite structure (LSC-IR-SSC-IR) and with full sizes ranging from 75 to 111 Kbp. We observed a significant contraction of small single copy region (SSC, ranging from 0.4-29 Kbp) and expansion of inverted repeat region (IR, ranging from 6-30 Kbp), with C. deserticola and C. salsa showing the smallest SSCs with only one gene (rpl32). Compared with other Orobanchaceae species, Cistanche species showed extremely high rates of gene loss and pseudogenization, as reported for other parasitic Orobanchaceae species. Furthermore, analysis of sequence divergence on protein-coding genes showed the three genes (rpl22, clpP and ycf2) had undergone positive selection in the Cistanche species under study. In addition, by comparison of all available Cistanche plastomes we found 25 highly divergent intergenic spacer (IGS) regions that were used to predict two DNA barcode markers (Cis-mk01 and Cis-mk02 based on IGS region trnR-ACG-trnN-GUU) and eleven specific DNA barcode markers using Ecoprimer software. Experimental validation showed 100% species discrimination success rate with both type of markers.

CONCLUSION

Our findings have shown that Cistanche species are an ideal model to investigate the structure variation, gene loss and pseudogenization during the process of plastome evolution in parasitic species, providing new insights into the evolutionary relationships among the Cistanche species. In addition, the developed DNA barcodes markers allow the proper species identification, ensuring the effective and safe use of Cistanche species as medicinal products.