Bacterial Succession during Vermicomposting of Silver Wattle (Acacia dealbata Link)

Vermicomposting is the process of organic waste degradation through interactions between earthworms and microbes. A variety of organic wastes can be vermicomposted, producing a nutrient-rich final product that can be used as a soil biofertilizer. Giving the prolific invasive nature of the Australian silver wattle Acacia dealbata Link in Europe, it is important to find alternatives for its sustainable use. However, optimization of vermicomposting needs further comprehension of the fundamental microbial processes. Here, we characterized bacterial succession during the vermicomposting of silver wattle during 56 days using the earthworm species Eisenia andrei. We observed significant differences in α- and β-diversity between fresh silver wattle (day 0) and days 14 and 28, while the bacterial community seemed more stable between days 28 and 56. Accordingly, during the first 28 days, a higher number of taxa experienced significant changes in relative abundance. A microbiome core composed of 10 amplicon sequence variants was identified during the vermicomposting of silver wattle (days 14 to 56). Finally, predicted functional profiles of genes involved in cellulose metabolism, nitrification, and salicylic acid also changed significantly during vermicomposting. This study, hence, provides detailed insights of the bacterial succession occurring during vermicomposting of the silver wattle and the characteristics of its final product as a sustainable plant biofertilizer.

Antifungal Activity of Earthworm Coelomic Fluid Obtained from Eisenia andrei, Dendrobaena veneta and Allolobophora chlorotica on Six Species of Phytopathogenic Fungi

The functioning of soil ecosystems greatly depends on the interactions occurring between soil biota communities. It is well known that earthworms are an important soil component that substantially affects its function, including their meaningful impact on the development of different phytopathogenic soil fungi. Phytopathogenic fungi are responsible for crop disease and cause great economic damage. It has previously been established that earthworms’ coelomic fluid can suppress the growth of phytopathogenic fungi, but the exact molecular mechanism is unknown. The present study aimed at broadening the proof of this observed phenomenon by investigating the effects of the coelomic fluid extract of three different earthworm species (Eisenia andrei, Dendrobaena veneta and Allolobophora chlorotica) on the growth of six different phytopathogenic fungi species (Berkeleyomyces basicola, Fusarium culmorum, Globisporangium irregulare, Rhizoctonia solani, Macrophomina phaseolina, and Sclerotinia sclerotiorum). Coelomic fluid extract was obtained by electrostimulation or usage of extraction buffer (only in case of A. chlorotica) and prepared in three different concentrations by diluting the obtained coelomic fluid with physiological saline. The coelomic fluid extract of the three investigated earthworm species had an inhibitory effect on the growth of all six phytopathogenic fungi species. The greatest inhibitory effect was achieved with the E. andrei coelomic fluid extract reducing the growth of R. solani fungi. The findings of this research confirm the antifungal activity of coelomic fluid obtained from earthworm species belonging to different ecological categories and may be of potential use in crop protection against phytopathogenic fungi.

Carbon Dioxide and Methane Emissions during the Composting and Vermicomposting of Sewage Sludge under the Effect of Different Proportions of Straw Pellets

The aim of this study was to evaluate the carbon dioxide (CO2) and methane (CH4) emissions during the composting and vermicomposting of sewage sludge under the effect of different proportions of straw pellets. Four treatments, including a control with three replicates, were designed to mix the initial sewage sludge with varying rates of pelletized wheat straw (0, 25%, 50%, and 75% (w/w)). Over a 60-day period, vermicomposting with Eisenia andrei treatments and composting were carried out. The results indicated that both composting and vermicomposting produce a significant (p < 0.001) amount of CO2 and CH4 emissions from all treatments. Vermicomposting significantly reduced CH4 emissions by 18%, 34%, and 38% and increased CO2 emissions by 75%, 64%, and 89% for the treatments containing 25%, 50%, and 75% straw pellets, respectively, compared to composting. However, CO2 emissions decreased and CH4 emissions increased during composting compared to vermicomposting. As a result of this finding, both composting and vermicomposting processes are recommended as an additive of pelletized wheat straw, depending on the target gas to be reduced.