Grassland fairy rings of Leucocalocybe mongolica represent the center of a rich soil microbial community

Fungal fairy rings: history, ecology, dynamics and engineering functions

Fungal fairy rings (FFR) are fascinating natural phenomena that have intrigued people and scientists for centuries. These patterns, often represented by circular distributions of altered vegetation, are found in grasslands and forest habitats. Fairy rings occur when fungi grow radially in the soil, raising from a central point, progressively degrading organic matter and thus affecting vegetation. The observation of such spatial patterns allows mycologists to conduct an in-depth analysis of the role of fungi in ecosystems. This review presents the current knowledge and scientific advancement of the studies of FFRs. An historical appraisal from the most representative pioneer studies until recent works is presented in different scientific fields, including microbiology, chemistry, botany and ecology. Based on a deep analysis of bibliographic data, we synopsised different aspects of FFRs: i) history of studies, ii) taxonomy, iii) ecology (environmental conditions and biogeography), iv) classification of vegetation patterns, v) spatial dynamics, vi) role as ecosystem engineer (impact on soil chemistry, plants and microbiota). In conclusion, beside still open research areas requiring further investigation, a schematic functional model of fungal fairy rings is proposed, in which on one hand the dynamics of the fungal mycelium is explained by self-DNA accumulation and the build-up of autotoxicity. On the other hand, the effects of fungi on plants are related to the intermingled and differently spatially distributed effects of hydrophobicity, phytotoxicity and phytostimulation.

Intercropping of Saccharum spp. with Dictyophora indusiata: effects on microbial communities and metabolite profiles during bagasse degradation

Background

Intercropping Saccharum spp. (sugarcane) with the fungus Dictyophora indusiata together with bagasse amendment represents an innovative circular agriculture method that can enhance soil health, boost sugarcane yields, and increase farm profitability. Understanding the process by which D. indusiata degrades bagasse is key to optimizing this method.

Aims

This study aims to clarify the microbial and metabolic processes involved in bagasse degradation by D. indusiata in the sugarcane intercropping system.

Methods

Chemical composition analysis, metabarcoding sequencing, and metabolomic profiling were conducted on D. indusiata-degraded bagasse (DIBA) and naturally degraded bagasse (BA).

Results

Analysis of chemical composition revealed that only acid detergent fiber (ADF) and crude protein content differed significantly between the DIBA and BA treatments. Metabarcoding sequencing showed that DIBA significantly altered the bacterial and fungal communities, reducing microbial diversity. Metabolomic analysis indicated an enhancement of biological metabolism, particularly carbohydrate breakdown, in the DIBA treatment. Key metabolites, such as glucose, cellobiose, and D-mannose, were more abundant in DIBA samples. In addition, unique metabolites such as L-alanine, serine, and oxaloacetate were detected in the DIBA treatment, suggesting more efficient bagasse degradation compared with natural processes.

Conclusion

The use of macrofungi such as D. indusiata can play a pivotal role in circular agriculture by transforming agricultural waste into valuable soil amendments. Future research should focus on the long-term impact of this system on soil quality and crop yield, as well as the underlying mechanisms, to further optimize intercropping systems and the use of fungi in agricultural waste management.

Macrofungi promote SOC decomposition and weaken sequestration by modulating soil microbial function in temperate steppe

Soil organic carbon (SOC) sequestration is a key grassland ecosystem function, and the magnitude of SOC reservoirs depends on microbial involvement, especially that of fungi. Mycelia developed by macrofungi potentially influence carbon (C) fixation and decomposition; however, the mechanisms underlying their effects on SOC storage in grassland ecosystems remain poorly understood. The fairy rings formed by macrofungi in grasslands are natural platform for exploring macrofungal effects on SOC. In this study, we collected topsoil (0-10 cm) from four different fairy ring zones in a temperate steppe to reveal the macrofungal effects on SOC fractions, including particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), and the SOC storage microbial mechanism using metagenomic sequencing technology. Both POC and MAOC decreased after macrofungal passage, resulting in a 7.37 % reduction in SOC. Macrofungal presence reduced microbial biomass carbon (MBC), but significantly enhanced the β-1,4-glucosidase (BG) activity, which increased dissolved organic carbon (DOC). In addition, the abundance of copiotrophs (Proteobacteria and Bacteroidetes) with lower C metabolic rates increased, and that of oligotrophs (Actinobacteria, Acidobacteria, Chloroflexi, and Verrucomicrobia) with higher substrate utilization efficiency decreased in the presence of macrofungi. This may further promote SOC decomposition. Correspondingly, there was a lower abundance of C-fixation genes but more C-degradation genes (especially hemicellulosic degradation genes) during macrofungal passage. Our results indicate that the presence of macrofungi can modulate the soil microbial community and functional genes to reduce SOC storage by inhibiting microbial C sequestration while promoting C decomposition in grassland ecosystems. These findings refine our mechanistic understanding of SOC persistence through the interactions between macrofungi and other microbes.

Morchella esculenta cultivation in fallow paddy fields and drylands affects the diversity of soil bacteria and soil chemical properties

The properties of paddy field (DT) and dry land (HD) soil and food production can be enhanced by the cultivation of Morchella esculenta (ME) during the fallow period. However, whether ME cultivation affects the soil health and microbial diversity of paddy fields and drylands during the cultivation period remains unclear, and this has greatly limited the wider use of this cultivation model. Here, we analyzed the soil chemical properties and bacterial diversity (via metabarcoding sequencing) of DT and HD soils following ME cultivation. Our findings indicated that ME cultivation could enhance soil health. The content of soil phosphorus and potassium (K) was increased in DT soil under ME cultivation, and the K content was significantly higher in HD soil than in DT soil under ME cultivation. ME cultivation had a weak effect on alpha diversity, and ME cultivation affected the abundance of some genera of soil bacteria. The cultivation of ME might reduce the methane production capacity of DT soil and enhance the nitrogen cycling process of HD soil based on the results of functional annotation analysis. Network analysis and correlation analysis showed that Gemmatimonas, Bryobacter, and Anaeromyxobacter were the key bacterial genera regulating soil chemical properties in DT soil under ME cultivation, and Bryobacter, Bacillus, Streptomyces, and Paenarthrobacter were the key taxa associated with the accumulation of K in HD soil. The results of our study will aid future efforts to further improve this cultivation model.

Soil chemistry, metabarcoding, and metabolome analyses reveal that a sugarcane-Dictyophora indusiata intercropping system can enhance soil health by reducing soil nitrogen loss

Introduction

Greater amounts of fertilizer are applied every year to meet the growing demand for food. Sugarcane is one of the important food sources for human beings.

Methods

Here, we evaluated the effects of a sugarcane-Dictyophora indusiata (DI) intercropping system on soil health by conducting an experiment with three different treatments: (1) bagasse application (BAS process), (2) bagasse + DI (DIS process), and (3) the control (CK). We then analyzed soil chemistry, the diversity of soil bacteria and fungi, and the composition of metabolites to clarify the mechanism underlying the effects of this intercropping system on soil properties.

Results and discussion

Soil chemistry analyses revealed that the content of several soil nutrients such as nitrogen (N) and phosphorus (P) was higher in the BAS process than in the CK. In the DIS process, a large amount of soil P was consumed by DI. At the same time, the urease activity was inhibited, thus slowing down the loss of soil in the DI process, while the activity of other enzymes such as β-glucosidase and laccase was increased. It was also noticed that the content of lanthanum and calcium was higher in the BAS process than in the other treatments, and DI did not significantly alter the concentrations of these soil metal ions. Bacterial diversity was higher in the BAS process than in the other treatments, and fungal diversity was lower in the DIS process than in the other treatments. The soil metabolome analysis revealed that the abundance of carbohydrate metabolites was significantly lower in the BAS process than in the CK and the DIS process. The abundance of D(+)-talose was correlated with the content of soil nutrients. Path analysis revealed that the content of soil nutrients in the DIS process was mainly affected by fungi, bacteria, the soil metabolome, and soil enzyme activity. Our findings indicate that the sugarcane-DIS intercropping system can enhance soil health.

Assessment of the rhizosphere fungi and bacteria recruited by sugarcane during smut invasion

Whip smut is one of the most serious and widely spread sugarcane diseases. Plant-associated microbes play various roles in conferring advantages to the host plant. Understanding the microbes associated with sugarcane roots will help develop strategies for the biocontrol of smut. Therefore, the present study explored microbe-mediated sugarcane response to smut invasion via 16S rRNA and ITS metabarcoding survey of the rhizosphere soils of resistant and susceptible sugarcane varieties. The bacterial and fungal diversity in the rhizosphere soils differed between the resistant and susceptible varieties. The bacterial genera Sphingomonas, Microcoleus_Es-Yyy1400, Marmoricola, Reyranella, Promicromonospora, Iamia, Phenylobacterium, Aridibacter, Actinophytocola, and Edaphobacter and one fungal genus Cyphellophora were found associated with smut resistance in sugarcane. Detailed analysis revealed that the majority of bacteria were beneficial, including the actinomycete Marmoricola and Iamia and Reyranella with denitrification activity. Analysis of bacterial network interaction showed that three major groups interacted during smut invasion. Meanwhile, seven of these genera appeared to interact and promote each other's growth. Finally, functional annotation based on the Functional Annotation of Prokaryotic Taxa (FAPROTAX) database predicted that the abundant bacteria are dominated by oxygenic photoautotrophy, photoautotrophy, and phototrophy functions, which may be related to smut resistance in sugarcane. The present study thus provides new insights into the dynamics of the sugarcane rhizosphere microbial community during smut invasion.

Metabarcoding and Metabolome Analyses Reveal Mechanisms of Leymus chinensis Growth Promotion by Fairy Ring of Leucocalocybe mongolica

Fairy rings are a unique ecological phenomenon caused by the growth of the fungal mycelium in the soil. Fairy rings formed by Leucocalocybe mongolica (LM) are generally distributed in the Mongolian Plateau, where they promote plant growth without fertilization and alleviate fertilizer use. We previously investigated the soil factors regulating growth promotion in a fairy ring ecosystem; however, the aspects of the plant (Leymus chinensis, LC) that promote growth have not been explored. Therefore, the present study investigated the endophyte diversity and metabolome of LC in an LM fairy ring ecosystem. We analyzed the leaf and root samples of LC from the DARK (FR) and OUT (CK) zones. The fairy rings significantly improved the fungal diversity of roots and leaves and the bacterial diversity of leaves in the FR zone. Ralstonia was the dominant bacteria detected in the LC leaves. In addition, Marasmius, another fairy ring fungal genus, was also detected with a high abundance in the roots of the FR zone. Furthermore, widely targeted metabolome analysis combined with KEGG annotation identified 1011 novel metabolites from the leaves and roots of LC and seven pathways significantly regulated by the fairy ring in the FR zone. The fairy ring ecosystem significantly downregulated the flavonoid metabolism in the leaves and roots of LC. The correlation analysis found Ralstonia is a potential regulatory factor of flavonoid biosynthesis in LC. In addition, salicylic acid and jasmonic acid were found upregulated in the leaves, probably related to Marasmius enrichment. Thus, the study details plant factors associated with enhanced growth in an LM fairy ring ecosystem. These findings lay a theoretical foundation for developing the fairy ring ecosystem in an agricultural system.

High-throughput sequencing reveals soil bacterial community structure and their interactions with environmental factors of the grassland fairy ring

Fairy rings (FRs) are common ecological grassland landscapes that have been studied for a long time. However, little is known about their interactions with soil physicochemical properties and bacterial communities. This study performed high-throughput sequencing of the 16S rRNA V3-V4 variable regions of soil bacteria in the three concentric zones of chosen FR, namely, the ON zone, on the ring; IN zone, inside the ring; and OUT zone, outside the ring. Also, the change in physicochemical properties and enzyme activities of the soil were determined. This study found that the nutrients and enzyme activities on the ring were higher than inside and outside of the ring. The activities of microorganisms were frequent and the plant grew splendidly. The bacterial species diversity was the lowest on the ring with the main genera Pseudonocardia, Streptosporangium, Kribbella and Promicromonospora. The imbalance of the microbial community structure at different ring zones may be the driving factor for the continuous outward expansion of FRs. Soil available phosphorus, electrical conductivity, total nitrogen and organic matter positively correlated with the distribution of FR soil bacteria.

Soil Chemical Properties, Metabolome, and Metabarcoding Give the New Insights into the Soil Transforming Process of Fairy Ring Fungi Leucocalocybe mongolica

A unique ecological landscape distributed in the Mongolian Plateau, called fairy rings, caused by the growth of the fungus Leucocalocybe mongolica (LM) in the soil could promote plant growth without fertilization. Therefore, this landscape can alleviate fertilizer use and has excellent value for agricultural production. The previous studies only investigated several parameters of the fairy rings, such as soil microbial diversity and some soil chemical properties, thus conclusions based on the studies on fairy rings lack comprehension. Therefore, the present study systematically investigated the chemical properties, metabolome, and metabarcoding of LM-transformed soil. We analyzed fairy ring soils from DARK (FR) and OUT (CK) zone correlated growth promotion with ten soil chemical properties, including N, nitrate-N, inorganic-P, cellulose, available boron, available sulfur, Fe, Mn, Zn, and Cu, which were identified as important markers to screen fairy ring landscapes. Metabolomics showed that the accumulation of 17 carbohydrate-dominated metabolites was closely associated with plant growth promotion. Finally, metabarcoding detected fungi as the main components affecting soil conversion. Among the various fungi at the family level, Lasiosphaeriaceae, unidentified_Auriculariales_sp, and Herpotrichiellaceae were markers to screen fairy ring. Our study is novel and systematically reveals the fairy ring soil ecology and lists the key factors promoting plant growth. These findings lay a theoretical foundation for developing the fairy ring landscape in an agricultural system.