Addition Of Earthworms Research Articles

Earthworms-enhanced bacterial degradation of the chiral fungicide penflufen R-enantiomer

The widespread application of chiral fungicides as seed-coating agents in agriculture has led to serious residue accumulation in soil, increasingly drawing attention to soil pollution remediation strategies for chiral pesticides. This study explored the role of earthworms and soil microorganisms in selectively accelerating the degradation of penflufen in soil. The results showed that soil microorganisms significantly accelerated penflufen enantiomer degradation, particularly the R-enantiomer. Nocardioides, Variovorax, Arthrobacter, and Pseudomonas were identified as key degrading microorganisms associated with the preferential degradation of the R-enantiomer. The addition of earthworms further significantly enhanced the preferential degradation of the R-enantiomer. Importantly, earthworms markedly promoted the growth and reproduction of the four aforementioned degrading microorganisms in soil treated with enantiomers. Notably, the relative abundance of these degrading microorganisms was significantly higher in R-enantiomer-treated soil with earthworms than in soil treated with the S-enantiomer. Additionally, earthworms significantly increased the relative abundance of degradation genes p450, bphA1, and benA in the soil, especially in the R-enantiomer treated soil. Nocardioides, Variovorax, Arthrobacter, and Pseudomonas were identified as potential hosts for the degradation gene benA. More importantly, twelve strains of penflufen-degrading bacteria were isolated from the treated soil, of which eight belonged to the aforementioned four microorganisms and exhibited a remarkable ability to preferentially degrade the R-enantiomer. This finding highlights the potential of adding earthworms to soil, in conjunction with key degrading microorganisms, which preferentially accelerates penflufen R-enantiomer degradation.

The Ability of Earthworms to Influence the Ratio of C/N during Vermicomposting Process from Different Remnants

This study aimed to investigate the carbon to nitrogen ratio (C/N) in vermicomposts produced from mixtures of cabbage, beans, and tea remnants combined with cardboard at a 1:1 ratio, totaling 2 kilograms, using two different types of worms: Lumbricus terrestris and Eisenia fetida. The results indicated that vermicompost produced by Eisenia fetida exhibited a significant decrease in C/N ratio by 18.60, whereas that produced by Lumbricus terrestris had a C/N ratio of 20.723. Regarding interactions, the highest initial C/N ratio among cabbage remnants, irrespective of worm type, was 25.000, whereas the lowest ratio after processing was 1.936 for tea remnants, showing significant differences. Across all remnants, there was a consistent decrease in C/N ratio post-processing, with cabbage remnants exhibiting the highest initial ratio of 25.00 before earthworm addition and tea remnants showing the lowest ratio of 8.530 after earthworm processing, indicating significant variation

Roxarsone reduces earthworm-mediated nutrient cycling by suppressing aggregate formation and enzymic activity in soil with manure application

The application of manure and earthworms are frequently used in fertilization practices to improve C, N, and P cycling in soil, which may be adversely affected by roxarsone (ROX), as an organoarsenical pollutant. To effectively address this issue, in this work, the interactive impacts of ROX and earthworm Eisenia foetida on the aggregate formation, input of organic carbon (OC), and changes in the available N and P following 56-day cultivation were systematically investigated. Compared to the control, earthworms increased the mean weight diameter (MWD) of the soil aggregates from 0.6 to 1.1 mm. Thereby, they activated soil enzymes including catalase (CAT), sucrase (SC), urease (UE), and neutral phosphatase (NP), with the soil's pH decreased to 7.1. Consequently, the values of OC, soluble nitrite (NO3-N), and Olsen-P content were respectively increased by 0.78-, 1.69-, and 0.87- folds in the E treatment (14.3 vs. 25.5 g/kg, 12.8 vs. 33.3 mg/kg, and 7.8 vs. 14.6 mg/kg). Although the changes in the R treatment were slight, ROX reduced the earthworm-mediated improvements of soil fertility during the application of the RE treatment compared to the E treatment, i.e., the values of MWD, OC, NO3-N, and Olsen-P were reduced to 0.9 mm, 20.4 g/kg, 25.4 mg/kg, and 11.6 mg/kg, respectively. From the well-fitted structural equation models, it was demonstrated that earthworms enhanced the aggregate formation and nutrient cycling of OC, NO3-N, and Olsen-P, which were inhibited by ROX. Overall, these adverse effects can be offset by earthworm addition, which can play the dual role of monitor and driver for the soil properties. Our work provides insightful strategies for ROX-bearing manure management.

Enhancing remediation efficiency of hyperaccumulators through earthworm addition: Evidence from a pot study on cadmium-contaminated soil

Soil cadmium (Cd) contamination is an urgent environmental problem, which endangers human health through the food chain. Bioremediation attracted extensive attention around the world due to the high cost-efficiency. However, the remediation efficiency of different plant and earthworm species of soil Cd pollution is still unclear, it is thus of great significance to explore the combined effects of different remediation plants and earthworm species to improve the bioremediation capacity. In the present study, we consequently selected three species of Cd hyperaccumulator plants (vetiver, P. vittata and S. emarginatum) and three species of earthworms (E. fetida P1, E. fetida P2, and P. guillelmi) to compare the differences in Cd accumulation among various earthworm-plant combinations. Results indicated that the changes of soil pH and SOM in plant-animal combined application induced the higher soil Cd removal efficiency. The Cd removal efficiency showed highest in combination groups P. vittata-E. fetida P2 and P. vittata-P. guillelmi. Meanwhile, the improvements of biomass of plants and animals also were consistent with the increasing of Cd concentration in both plants and earthworms after combined application. It showed that the Cd concentrations in P. vittata were the highest while the TFs of Cd in S. emarginatum displays significantly more than that in others. In conclusion, the recommended combined system of earthworm-plant (P. vittata-E. fetida P2 and P. vittata-P. guillelmi) to provide reference for soil Cd bioremediation system in practice.

Earthworms improve the rhizosphere micro-environment to mitigate the toxicity of microplastics to tomato (Solanum lycopersicum)

Microplastics (MPs) are widespread in agricultural soil, potentially threatening soil environmental quality and plant growth. However, toxicological research on MPs has mainly been limited to individual components (such as plants, microbes, and animals), without considering their interactions. Here, we examined earthworm-mediated effects on tomato growth and the rhizosphere micro-environment under MPs contamination. Earthworms (Eisenia fetida) mitigated the growth-inhibiting effect of MPs on tomato plant. Particularly, when exposed to environmentally relevant concentrations (ERC, 0.02% w/w) of MPs, the addition of earthworms significantly (p < 0.05) increased shoot and root dry weight by 12–13% and 13–14%, respectively. MPs significantly reduced (p < 0.05) soil ammonium (NH4+-N) (0.55–0.69 mg/kg), nitrate nitrogen (NO3−-N) (7.02–8.65 mg/kg) contents, and N cycle related enzyme activities (33.47–42.39 μg/h/g) by 37.7–50.9%, 22.6–37.2%, and 34.2–48.0%, respectively, while earthworms significantly enhanced (p < 0.05) inorganic N mineralization and bioavailability. Furthermore, earthworms increased bacterial network complexity, thereby enhancing the robustness of the bacterial system to resist soil MPs stress. Meanwhile, partial least squares modelling showed that earthworms significantly influenced (p < 0.01) soil nutrients, which in turn significantly affected (p < 0.01) plant growth. Therefore, the comprehensive consideration of soil ecological composition is important for assessing MPs ecological risk.

Evaluating drained water quality in a pilot worm-sludge treatment reed bed planted with Arundo donnas in the Mediterranean climate

This study evaluated the impact of incorporating earthworms (Eisenia fetida) on the drained water quality from a sludge treatment reed bed. The experiment encompassed four setups of treatment beds in two replicates: planted with Arundo donax and addition of earthworms, planted without earthworms, unplanted with earthworms, and treatment bed without plants nor earthworms as control. The units were fed every two weeks with mixed sewage sludge, a blend of primary and secondary sludge over 24 cycles. The mixed sewage sludge had mean dry and volatile solid contents of 24.71 g.DS.L−1 (± 13.67) and 19.14 g.VS.L−1 (± 10.29) resulting a sludge loading rate of 43.59 kg.DS.m−2.year−1 (± 14.49). The inclusion of earthworms in the planted unit reduced release masses of total suspended solids, chemical oxygen demand, nitrate and phosphorous by 43, 45, 75 and 45 % compared to the planted unit. Plant biomass production increased by 43 % with the earthworm presence. The removal efficiency of the units improved after a ramp-up phase (after six months feeding) of which the concentration of TSS, COD and Escherichia coli met limits for water reuse while nitrogen components and phosphorous surpassed the limits. The planted unit with earthworms removed 99 and 99 % of TSS and COD, respectively. Overall, water loss namely through evapotranspiration and earthworm hydration need, positively correlated with pollutant concentration, and earthworm-planted unit had 46 % higher water loss compared to control unit.

The responses of CO2 emission to nitrogen application and earthworm addition in the soybean cropland.

The effects of nitrogen application or earthworms on soil respiration in the Huang-Huai-Hai Plain of China have received increasing attention. However, the response of soil carbon dioxide (CO2) emission to nitrogen application and earthworm addition is still unclear. A field experiment with nitrogen application frequency and earthworm addition was conducted in the Huang-Huai-Hai Plain. Results showed nitrogen application frequency had a significant effect on soil respiration, but neither earthworms nor their interaction with nitrogen application frequency were significant. Low-frequency nitrogen application (NL) significantly increased soil respiration by 25%, while high-frequency nitrogen application (NH), earthworm addition (E), earthworm and high-frequency nitrogen application (E*NH), and earthworm and low-frequency nitrogen application (E*NL) also increased soil respiration by 21%, 21%, 12%, and 11%, respectively. The main reason for the rise in soil respiration was alterations in the bacterial richness and keystone taxa (Myxococcales). The NH resulted in higher soil nitrogen levels compared to NL, but NL had the highest bacterial richness. The abundance of Corynebacteriales and Gammaproteobacteria were positively connected with the CO2 emissions, while Myxococcales, Thermoleophilia, and Verrucomicrobia were negatively correlated. Our findings indicate the ecological importance of bacterial communities in regulating the carbon cycle in the Huang-Huai-Hai Plain.

How do earthworms affect the pathway of sludge bio-stabilization via vermicomposting?

The synergy effects between earthworms and microorganisms promote nitrogen mineralization and enhance stabilization of organic matters in a vermicomposting system. However, the stabilization pathways of vermicomposting in the system remain unknown. The aim of this study was to investigate the effect of earthworms on the stabilization pathway and associated microbial population of waste activated sludge recycled by vermicomposting. The treatment of sludge with and without earthworms was conducted at 20 °C for 60 days. The trends in organic matter (OM), dissolved organic carbon (DOC), NH4+-N, electrical conductivity (EC), microbial biomass carbon (MBC), and dehydrogenase activity (DHA) were similar in both systems over time. At the end of the treatment, OM and DOC were significantly lower (p < 0.05), and EC, NH4+-N, and NO3−-N were significantly higher (p < 0.05) in the vermicomposting group than in the control. Based on the statistical results of principal component analysis (PCA), it was proposed that the stabilization pathway in both treatment systems required a sequence of reactions characterized by the degradation of organic matter, accumulation of dissolved organic carbon, ammonification, and nitrification. Vermicomposting led to greater abundance and diversity (Shannon index) of 16S rDNA microbial species, but more even distribution in microbial community composition (Simpson index) than the control. However, the opposite performance for 18S rDNA microbes was observed. Vermicomposting enhanced the abundance of microorganisms involved in organic matter degradation and nitrification, facilitating the conversion of organic matter and favoring the nitrification. In short, the pathway of sludge bio-stabilization is not altered regardless of the addition of earthworms or not, which enables us to better understand vermicomposting process of sludge.

Appropriateness of introducing earthworms into sustainable agriculture from the perspective of soil carbon emissions

Sustainable agriculture, as an effective method for reducing the risk of soil degradation, is often accompanied by increases in soil fauna populations. However, the effects of soil fauna (such as earthworms) bioturbation on soil carbon (C) emissions remain unclear. We conducted a 31-day incubation experiment to measure the effects of adding straw (1 g) and anecic earthworms on the burrowing characteristics and C emissions using two soils collected from the plow layer and plow pan layers. We also explored the effects of the soil C source (soil organic C (SOC) and exogenous organic matter (OM) inputs) on the soil C emissions induced in the presence of earthworms by meta-analysis. The incubation experiment showed that earthworms increased the loss rate of surface straw (49.4–96.8%; p < 0.05) and the soil C emissions (160.5–455.4%; p < 0.01). Earthworms significantly increased the macroporosity (p < 0.001) and macropore size (p = 0.016), but decreased the macropore number in the plow layer soil. While, only the soil macropore size increased significantly (p = 0.025) under earthworm addition in the plow pan soil. Structural equation models indicated that straw directly influenced the soil macropore size (p = 0.022) and C emissions (p = 0.039) in the plow layer soil, but had no effects on the soil macropore characteristics and C emissions (p > 0.05) in the plow pan soil. Earthworms indirectly affected soil C emissions through effects on the soil macropore size (p < 0.05). Meta-analysis indicated that although earthworms increased C emissions by 51.7% and 25.0% without and with OM inputs (p > 0.224), respectively, the earthworm-induced effects on soil C emissions were not related to OM inputs (p = 0.337). Soil C emissions induced by earthworms decreased as the SOC content increased (from 45.1% to 2.6%), but these effects were not significant at any SOC level (p > 0.154). These findings indicate that the effects of anecic earthworms on soil C emissions can be reflected by the earthworm burrowing characteristics and earthworms increased the soil C emissions in the short term (incubation experiment), but their effects on soil C emissions eventually became non-significant due to reduced anecic-earthworm burrowing activities (most burrows are permanent or semi-permanent) and SOC content increase in the long term (meta-analysis). We therefore recommend that earthworm regulation together with OM inputs could be considered in sustainable agriculture.

Synergistic Interactions in Enzyme Activities During Vermiremediation of Heavy Metals (HMs) Polluted Soil: Elucidating the Impact of Eudrilus eugeniae

ABSTRACT The vermiremediation potential of Eudrilus eugeniae was assessed in heavy metals (HMs) contaminated soil in a microcosm experiment. In detail, efficacy of E. eugeniae was investigated in terms of reduction in HMs content, enhancement in the soil enzyme activities, synergistic correlation between the HMs and enzyme activities and bioaccumulation of HMs in the earthworm’s biomass. Moreover, a seed germination assay was also conducted to assess the HMs toxicity in soil after remediation. The results showed that Eudrilus eugeniae was capable of decreasing the Cu, Zn, Mn, Cr, and Ni contents in the soil by 17.56–26.30% after 90 days of experimental trial. Introduction of E. eugeniae increased cellulase, amylase, polyphenol oxidase, peroxidase, urease, dehydrogenase, and catalase activities by 30.3–80.95% compared to controls. Earthworm addition led to a 12.98% increase in G-Mean and 2.89% increase in T-QSI values, indicating significant soil health improvement. PCA revealed the negative impact of HMs on synergistic enzyme activities during vermiremediation. HMs content in earthworm biomass increased 13-fold. Seed germination assay confirmed HMs reduction by the end of the experiment. Thus, this study demonstrated the interconnected changes in the soil enzyme activities during vermiremediation of HMs from crude oil polluted soil.

Earthworms synergize with indigenous soil functional microorganisms to accelerate the preferential degradation of the highly toxic S-enantiomer of the fungicide imazalil in soil

The roles of soil and earthworm gut microorganisms in the degradation of the chiral fungicide imazalil (IMA) enantiomers were systemically studied in soil-earthworm systems. S-IMA degraded slower than R-IMA in soil without earthworms. After the addition of earthworms, S-IMA degraded faster than R-IMA. Methylibium was the potential degradative bacterium likely related to the preferential degradation of R-IMA in soil. However, the addition of earthworms significantly decreased the relative abundance of Methylibium, especially in R-IMA-treated soil. Meanwhile, a new potential degradative bacterium Aeromonas first appeared in soil-earthworm systems. Compared with enantiomer-treated soil, the relative abundance of indigenous soil bacterium Kaistobacter significantly boomed in enantiomer-treated soil with earthworms. Interestingly, Kaistobacter in the earthworm gut also obviously increased after exposure to enantiomers, particularly in S-IMA-treated soil, which was associated with the significant increase in Kaistobacter in soil. More importantly, the relative abundances of Aeromonas and Kaistobacter in S-IMA-treated soil were obviously higher than those in R-IMA-treated soil after the addition of earthworms. Moreover, these two potential degradative bacteria were also potential bacterial hosts of the biodegradation genes p450 and bph. Collectively, gut microorganisms are important helpers in soil pollution remediation by participating in the preferential degradation of S-IMA mediated by indigenous soil microorganisms.

Effects of different diets on growth performance, digestive enzyme activities and intestinal bacterial community of juvenile Chinese giant salamander (Andrias davidianus)

This study analyzed the growth performance, digestive enzyme activities and intestinal microbial community in HC group (fed with Chironomid larvae), HH group (fed with Chironomid larvae plus Earthworms) and QY group (fed with Earthworms) of juvenile Chinese giant salamander (Andrias davidianus) after farming for 60 days. The results showed that diet can affect the growth performance, digestive enzyme activities and intestinal mcirobiota composition of juvenile Chinese giant salamander. The growth performance in juvenile Chinese giant salamander of HC group was significantly higher than that of HH group and QY group. The ether extract content in muscles of juvenile Chinese giant salamander of HH group and QY group was significantly lower than that of HC group. The intestinal digestive enzyme activities in juvenile Chinese giant salamander of HC group were significantly lower than that of HH group and QY group. The intestinal microbial richness and diversity in juvenile Chinese giant salamander of HH group and QY group were significantly higher than that of HC group. The most dominant phylum of HC group and HH group was Firmicutes but QY group was Bacteroidota, and the most dominant genus of HC group was Clostridium_sensu_stricto_1 but HH group and QY group was Bacteroides. The 24 specific bacterial groups with different classification levels had significant differences in three diet groups of juvenile Chinese giant salamander and these specific bacteria were concentrated in Firmicutes, Proteobacteria and Bacteroidota. Thus, the above studies indicated that Chironomid larvae as diet can increase the growth performance of juvenile Chinese giant salamander, while the addition of Earthworms as diet can enhance digestive ability and change microbiota composition in intestine of juvenile Chinese giant salamander.

Arbuscular mycorrhizal fungi mitigate earthworm-induced N2O emissions from upland soil in a rice-rotated wheat farming system

Earthworms are important for soil processes in arable cropping systems, and affect the development of arbuscular mycorrhizal fungi (AMF) which may combinely play a crucial role in soil nitrogen (N) cycling. However, the information is limited about their interaction on N2O emissions. A two-factorial microcosm field experiment was established to identify the interactive effects of earthworms and AMF on N2O emissions from a rice-rotated wheat field and explore its underlying mechanisms about nitrification and denitrification processes. The results showed that earthworm addition (+E) increased cumulative N2O emissions during the whole growth stage by 236.7 % compared with no earthworms (−E). Cumulative N2O emissions during the jointing and booting stages contributed to 58.7 % of that during the whole growth stage. Higher N2O emissions under +E were attributed to changes in soil organic carbon (SOC) and NH4+ concentration. SOC was positively correlated to gene abundances associated with N2O reduction (e.g., nosZ), and earthworm activity enhanced SOC mineralization and reduced SOC concentration, thus increasing N2O emissions. A negative correlation between NH4+ and N2O emissions, and lower NH4+ under +E indicated that earthworms enhanced nitrification intensity using NH4+ as substrates. Interestingly, AMF normal (+A) significantly decreased cumulative N2O emissions by 37.3 % compared with mycorrhizal suppression (−A) and the interaction with earthworms can further decreased N2O emissions by 37.0 % compared with -E-A (P < 0.05). This can be explained by higher NH4+, lower NO3− concentrations, and lower abundance of nitrification-associated genes (e.g., AOA and AOB) at the booting stage under +A, suggesting that AMF reduced N2O emissions mainly through lowering nitrification intensity. The results highlight that earthworms increase N2O emissions while AMF can mitigate earthworm-induced N2O emissions, and enhance our understanding on the soil N cycle in terms of N2O production in the presence of AMF and earthworms.

Mitigation effects and microbial mechanism of two ecological earthworms on the uptake of chlortetracycline and antibiotic resistance genes in lettuce

The contamination of greenhouse vegetable soils with antibiotics and antibiotic resistance genes (ARGs), caused by the application of livestock and poultry manure, is a prominent environmental problem. In this study, the effects of two ecological earthworms (endogeic Metaphire guillelmi and epigeic Eisenia fetida) on the accumulation and transfer of chlortetracycline (CTC) and ARGs in a soil–lettuce system were studied via pot experiments. The results revealed that earthworm application accelerated the removal of the CTC from the soil and lettuce roots and leaves, with the CTC content reducing by 11.7–22.8 %, 15.7–36.1 %, and 8.93–19.6 % compared with that of the control, respectively. Both earthworms significantly reduced the CTC uptake by lettuce roots from the soil (P < 0.05) but did not change the CTC transfer efficiency from the roots to leaves. The high-throughput quantitative PCR results showed that the relative abundance of ARGs in the soil and lettuce roots and leaves decreased by 22.4–27.0 %, 25.1–44.1 %, and 24.4–25.4 %, respectively, with the application of earthworms. Earthworm addition decreased the interspecific bacterial interactions and the relative abundance of mobile genetic elements (MGEs), which helped reduce the dissemination of ARGs. Furthermore, some indigenous soil antibiotic degraders (Pseudomonas, Flavobacterium, Sphingobium, and Microbacterium) were stimulated by the earthworms. The results of redundancy analysis indicated that the bacterial community composition, CTC residues, and MGEs were the main parameters affecting the distribution of ARGs, accounting for 91.1 % of the total distribution. In addition, the bacterial function prediction results showed that the addition of earthworms reduced the abundance of some pathogenic bacteria in the system. Overall, our findings imply that earthworm application can substantially reduce the accumulation and transmission risk of antibiotics and ARGs in soil–lettuce systems, providing a cost-effective soil bioremediation practice for addressing antibiotic and ARGs contamination to guarantee the safety of vegetables and human health.

Effects of Earthworm, Straw, and Citric Acid on the Remediation of Zn, Pb, and Cd Contaminated Soil by Solanum photeinocarpum and Pterocypsela indica

Regulation of exogenous substances and intercropping are effective methods to improve the efficiency of phytoremediation of heavy metal contaminated soil. A pot experiment was used to study the effects of earthworms, straw, and citric acid on the remediation of Zn, Pb, and Cd contaminated soil by monocropping and intercropping of Solanum photeinocarpum and Pterocypsela indica. The results showed that the bioaccumulation factors (BCF) of earthworms for Zn, Pb, and Cd were 0.07-0.13, 0.10-0.26, and 5.64-15.52, respectively. The addition of straw in the soil increased the biomass of earthworms by 22.29%-223.87% but reduced the heavy metal concentrations by 8.15%-62.58%. Straw and citric acid showed passivation and activation effects, respectively, but earthworms had no significant effect on the available concentrations of heavy metals in the soil. Earthworms had no significant effect on the heavy metal concentrations of P. indica but reduced the heavy metal concentrations of S. photeinocarpum. Straw showed an inhibitory effect on the concentrations of heavy metals in P. indica but promoted the concentrations of Cd in S. photeinocarpum. Citric acid had no significant effect on the heavy metal concentrations in S. photeinocarpum but significantly increased the Pb concentrations in P. indica. Intercropping significantly reduced the soil available heavy metal concentrations and increased the heavy metal concentrations in plant roots; however, it had no significant effect on heavy metal concentrations in plant shoots. The total extraction amounts of Zn, Pb, and Cd by plants were mainly manifested as P. indica>intercropping>S. photeinocarpum. The addition of earthworms increased the total extraction amounts of Zn, Pb, and Cd by 12.49%, 35.89%, and 29.01%, respectively, and the addition of straw+earthworms increased the total extraction amounts of Pb by 87.21%. The results indicated that straw significantly promoted the growth of earthworms and reduced their accumulation of heavy metals, and the addition of earthworms alone or in combination with straw can effectively improve the remediation potential of P. indica of Zn, Pb, and Cd contaminated soil.

Co-composting of faecal sludge and carbon-rich wastes in the earthworm's synergistic cooperation system: Performance, global warming potential and key microbiome.

Composting is an effective alternative for recycling faecal sludge into organic fertilisers. A microflora-earthworm (Eisenia fetida) synergistic cooperation system was constructed to enhance the composting efficiency of faecal sludge. The impact of earthworms and carbon-rich wastes (rice straw (RS) and sawdust (S)) on compost properties, greenhouse gas emissions, and key microbial species of composting were evaluated. The addition of RS or S promoted earthworm growth and reproduction. The earthworm-based system reduced the volatile solid of the final substrate by 13.19-16.24 % and faecal Escherichia coli concentrations by 1.89-3.66 log10 cfu/g dry mass compared with the earthworm-free system. The earthworm-based system increased electrical conductivity by 0.322-1.402 mS/cm and reduced C/N by 56.16-64.73 %. The NH4+:NO3- ratio of the final faecal sludge and carbon-rich waste was <0.16. The seed germination index was higher than 80 %. These results indicate that earthworms contribute to faecal sludge maturation. Earthworm addition reduced CO2 production. The simultaneous addition of earthworms and RS system (FRS2) resulted in the lowest global warming potential (GWP). The microbial diversity increased significantly over time in the RS-only system, whereas it initially increased and later decreased in the FRS2 system. Cluster analysis revealed that earthworms had a more significant impact on the microbial community than the addition of carbon-rich waste. Co-occurrence networks for earthworm-based systems were simple than those for earthworm-free systems, but the major bacterial genera were more complicated. Highly abundant key species (norank_f_Chitinophagaceae and norank_f_Gemmatimonadaceae) are closely related. Microbes may be more cooperative than competitive, facilitating the conversion of carbon and nitrogen in earthworm-based systems. This work has demonstrated that using earthworms is an effective approach for promoting the efficiency of faecal sludge composting and reducing GWP.

Effects of straw returning combined with earthworm addition on nitrification and ammonia oxidizers in paddy soil.

Soil ammonia oxidation, which acts as the first and rate-limiting step of nitrification, is driven by ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and complete ammonia oxidizer (comammox, amoA gene of clade-A and clade-B). Straw returning, widely used ecological technology in China, is an effective measure for promoting straw decomposition and soil nutrient cycling when combined with earthworm addition. However, the effects of straw returning combined with earthworm addition on soil ammonia oxidizers remain poorly understood. A 2-year plot experiment was conducted with 5 treatments: no fertilizer (CK); regular fertilization (RT); straw returning (SR); earthworm addition (W); straw returning + earthworm addition (SRW). The AOA, AOB, comammox clade-A and clade-B community microbial diversities and structures were investigated by high-throughput sequencing. The results showed that (1) compared to RT treatment, W, SR, and SRW treatments all significantly increased the richness of AOA and comammox clade-A and clade-B (p < 0.05), and the richness of AOB was only significantly promoted by SRW treatment (p < 0.05). However, only SRW had a higher comammox clade-B diversity index than RT. (2) The ammonia oxidizer community structures were altered by both straw returning and earthworm addition. Soil NH4 +-N was the critical environmental driver for altering the ammonia oxidizer community structure. (3) Compared with RT treatment, the soil potential nitrification rate (PNR) of W and SRW treatments increased by 1.19 and 1.20 times, respectively. The PNR was significantly positively correlated with AOB abundance (path coefficient = 0.712, p < 0.05) and negatively correlated with clade-B abundance (path coefficient = -0.106, p < 0.05). This study provides scientific support for the application of straw returning combined with earthworm addition to improve soil nitrification with respect to soil ammonia-oxidizing microorganisms.

Straw incorporation interacting with earthworms mitigates N2O emissions from upland soil in a rice-wheat rotation system

Intensive attentions have been paid to the positive effects on nitrous oxide (N2O) production under straw return or the presence of earthworms. Straw return as a sustainable practice can promote earthworm growth, how the interactions between straw and earthworms affect N2O production is still not well known. A split-plot field experiment (straw return as main plot and earthworm addition as subplot) was performed to quantify the interactive effects of straw and earthworm on N2O emissions from a wheat field and to determine the underlying mechanisms from nitrification and denitrification processes. The results showed that straw return significantly increased N2O emissions by 41.0 % under no earthworm addition but decreased it by 19.0 % under earthworm addition compared with straw removal (P < 0.05). The significant interaction between straw and earthworm benefits the mitigation of N2O emissions. Random forest model showed that denitrification and nitrification were dominant processes to affect N2O emissions at the jointing and booting growth stages of wheat, respectively. The interaction between straw and earthworm significantly decreased the abundances of N2O-producing bacterial genes such as nirS and nirK at the jointing stages, and AOB at the booting stages. The contrasting mechanisms in regulating N2O emissions at different growth stages should be considered in nitrogen recycling models to accurately predict available N and N2O dynamics. Our findings suggest that N2O emissions under straw return can be weakened with the increasing earthworm populations under the scenario of widely used conservation practices (e.g., straw return and no-till) due to significant interaction between straw and earthworms.

Application of Rice Husk Biochar and Earthworm on Concentration and Speciation of Heavy Metals in Industrial Sludge Treatment.

The aim of this study was to assess the total concentration and speciation variation of heavy metals (Pb, Cd, Cu and Zn) during composting and vermicomposting of industrial sludge with different addition rations of rice husk biochar. Results indicated that pH, EC, total phosphorus (TP) and total potassium (TK) were increased and total organic carbon (TOC) and total nitrogen (TN) were decreased during the composting of industrial sludge with biochar compared with the control (sludge without biochar). The addition of earthworm to the biochar-amended sludge further decreased pH and TOC but highly enhanced the EC, TN, TP and TK. Comparatively lower concentrations of total and DTPA-extractable heavy metals were observed in biochar-amended sludge treatments mixed with earthworm in comparison with the biochar-amended sludge treatments without earthworm or the control. Sequential extraction methods demonstrated that vermicomposting of sludge with biochar converted more metals bound with exchangeable, carbonate and organic matter into the residual fraction in comparison with those composting treatments of sludge with biochar. As a result, the combination of rice husk biochar and earthworm accelerated the passivation of heavy metals in industrial sludge during vermicomposting. Rice husk biochar and earthworm can play a positive role in sequestering the metals during the treatment of industrial sludge. This research proposed a potential method to dispose the heavy metals in industrial sludge to transform waste into resource utilization.

Earthworms regulate the nematode community by directly enhancing the bacterial-based energy channel rather than through the effect of casts

Earthworms and their casts act as biocatalysts and regulators of the biotic and abiotic processes in soil ecosystems. However, the relative importance of the presence of earthworms and earthworm casts in affecting other soil biota remains underexplored. In this study, we conducted a manipulative mesocosm experiment in a 30-year-old subtropical broadleaved plantation forest to determine how epi-endogeic earthworms (Amynthas corticis) and their casts affect soil nematode communities individually and additively. We found that the addition of the epi-endogeic earthworms significantly increased the proportion of the Ba1 guild nematodes and enhanced the enrichment index of the soil nematode community, but decreased the channel index. These results indicate that the soils become enriched in nutrients with a higher activity in bacterial-based decomposition pathways in the presence of earthworms. However, cast addition alone had a minor effect on soil nematodes. Results of a redundancy analysis suggest that elevated contents of soil ammonium and available phosphorous were the major influencing factors on soil nematode abundances in the presence of epi-endogeic earthworms. Our results indicate that epi-endogeic earthworms rather than through their casts contributed to the structuring of the nematode communities and enhancing of the bacterial-based energy channel. This finding contributes to our understanding of soil biodiversity maintenance mechanisms and how the relationship of the soil biota affects their functions in soil food webs.