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

Evaluating the potential of digestate-loaded biochar in improving soil biological health and plant nutrition with less greenhouse gas emissions

Digestate has a great potential as a carbon (C) and nitrogen (N) soil amendment. Loading digestate onto biochar can produce a C- and N- enriched biochar fertilizer (i.e., digestate-loaded biochar, DLB), and help to solve digestate-specific issues. This study aims to evaluate the potential of DLB at optimal application rates in keeping plant (annual ryegrass) nutrition level while mitigating greenhouse gas emissions and improving soil biological health compared to chemical fertilizers in an acidic soil under liming or not. Soil biological health index was assessed through quantitative PCR and amplicon sequencing. The results showed that increasing DLB addition to 150 kg N ha-1 resulted in a similar N uptake of ryegrass to that under urea despite lower mineral N provided by DLB. This application rate decreased greenhouse gas emissions relative to urea, through decreasing CO2 emission despite increased CH4 emission. Compared to urea, this DLB rate did not change N2O emission, corresponding to the specifically increased abundance of nirK gene (1.3-fold) (and enriched denitrifier Dokdonella) for N2O production and nosZ clade I and II genes (87%) for N2O consumption. The DLB at 150 kg N ha-1 enhanced soil biological health index by 1.4-fold relative to urea through increasing microbial abundances particularly fungi, enriching beneficial microbes (plant-growth-promoting bacteria, mycorrhiza and dark-septate-endophyte), and increasing fungal diversity; this effect was less pronounced under liming. This study concludes that DLB can serve as an organic-mineral fertilizer in maintaining plant nutrition while decreasing greenhouse gas emissions and enhancing soil biological health, offering a sustainable approach to managing organic waste.

Effects of long-term continuous cropping on microbial community structure and function in tobacco rhizosphere soil

As is well known, continuous cropping can lead to a decrease in crop yield and quality. Despite this, continuous cropping remains prevalent in practical agricultural production, particularly in the case of tobacco cultivation, owing to its high economic value. The samples for this study were collected from a flue-cured tobacco planting base located in Huili County, Liangshan Yi Autonomous Prefecture, Sichuan Province, China. After years of continuous planting, the yield of tobacco in this base has significantly decreased. In order to explain the microecological causes of this phenomenon, we collected non-continuous cropping, continuous cropping for 5 years, and continuous cropping for 10 years of tobacco rhizosphere soil, and analyzed the effects of long-term continuous cropping on nutrients, enzyme activities, microbial community structure, and function of tobacco rhizosphere soil. The results showed that with the continuous cropping, the majority nutrients (except for phosphorus and manganese) in rhizosphere soil decreased significantly, and the rhizosphere microbial community structure changed significantly. Correlation network analysis results showed that changes in the rhizosphere microbial community of tobacco were closely related to soil urease, active organic carbon, and available iron content. The results of functional analysis based on microorganisms and genes showed that the rhizosphere microbiota may change the content of soil nutrients through iron_respiration, sulfur_respiration, and Carbon fixation in prokaryotes pathways. The results of the correlation network analysis and the functional analysis mutually confirmed each other, both emphasizing the important role of soil carbon and iron in shaping the structure of the tobacco rhizosphere microbial community. Based on the results of this study, we propose to improve the microbial community structure of tobacco rhizosphere soil by increasing the levels of readily oxidizable organic carbon, available iron, and soil urease activity in the future, so as to alleviate the negative impact of continuous cropping on crop yield. The results of this study provide theoretical support for modifying the rhizosphere microbial environment through nutrient regulation, thereby enhancing plant growth in the context of continuous tobacco cropping.

Analysis of rhizosphere soil microbial diversity and its functions between Dahongpao mother tree and cutting Dahongpao

Dahongpao mother tree (Camellia sinensis (L.) O. Ktze) is a representative of Wuyi rock tea. Whether there is a difference in rhizosphere soil microbial diversity and function between asexually propagated cuttings of Dahongpao (PD) and the parent Dahongpao mother tree (MD) has not been reported. In this study, high throughput sequencing technology was used to analyze rhizosphere soil microbial diversity, functions and their relationship with soil available nutrients and enzyme activities in MD and PD. The results showed that available nitrogen, phosphorus and potassium contents and urease, protease, acid phosphatase and sucrase activities of rhizosphere soils in MD were significantly higher than those in PD. Both bacterial and fungal diversity were higher in rhizosphere soils in MD than in PD, and secondly, the bacterial community structure was less stable while the fungal community structure was more stable in PD compared to MD. There were significant differences between MD and PD tea tree rhizosphere soils in 6 genera of characteristic bacteria and 4 genera of characteristic fungi. The results of function and interaction effect analysis showed that the rhizosphere soil available nutrient content and enzyme activities in MD were significantly higher than those in PD, and their contributions mainly originated from Pirellula and Acidisphaera of characteristic bacteria and Alatospora of characteristic fungi. Secondly, MD maybe had a stronger ability to inhibit soil pathogens than PD, with the main contribution coming from Scopulariopsis and Tolypocladium of characteristic fungi. Overall, compared with PD, soil texture in MD was relatively better, and its soil nutrient cycling-related enzyme activities were stronger, which was more favorable to soil nutrient cycling and increased the available nutrient content of the soil, which in turn promoted the growth of tea trees. This study provides an important reference for the planting and management of tea tree cuttings and microbial regulation of tea tree growth.

Mechanisms of intestinal injury in polychaete Perinereis aibuhitensis caused by low-concentration fluorene pollution: Microbiome and metabonomic analyses

The polychaete Perinereis aibuhitensis is used for bioremediation; however, its ability to remove fluorene, a common environmental pollutant, from sediments remains unclear, especially at low concentrations of fluorene (10 mg/kg). In this study, we explored the mechanism of intestinal injury induced by low concentrations of fluorene and the reason intestinal injury is alleviated in high fluorene concentration groups (100 and 1000 mg/kg) using histology, ecological biomarkers, gut microbiome, and metabolic response analyses. The results show that P. aibuhitensis showed high tolerance to fluorene in sediments, with clearance rates ranging 25-50 %. However, the remediation effect at low fluorene concentrations (10 mg/kg) was poor. This is attributed to promoting the growth of harmful microorganisms such as Microvirga, which can cause metabolic disorders, intestinal flora imbalances, and the generation of harmful substances such as 2-hydroxyfluorene. These can result in severe intestinal injury in P. aibuhitensis, reducing its fluorene clearance rate. However, high fluorene concentrations (100 and 1000 mg/kg) may promote the growth of beneficial microorganisms such as Faecalibacterium, which can replace the dominant harmful microorganisms and improve metabolism to reverse the intestinal injury caused by low fluorene concentrations, ultimately restoring the fluorene-removal ability of P. aibuhitensis. This study demonstrates an effective method for evaluating the potential ecological risks of fluorene pollution in marine sediments and provides guidance for using P. aibuhitensis for remediation.