Effect of organic amendments obtained from different pretreatment technologies on soil microbial community.

The application of organic amendments (OAs) obtained from biological treatment technologies is a common agricultural practice to increase soil functionality and fertility. OAs and their respective pretreatment processes have been extensively studied. However, comparing the properties of OAs obtained from different pretreatment processes remains challenging. In most cases, the organic residues used to produce OAs exhibit intrinsic variability and differ in origin and composition. In addition, few studies have focused on comparing OAs from different pretreatment processes in the soil microbiome, and the extent to which OAs affect the soil microbial community remains unclear. This limits the design and implementation of effective pretreatments aimed at reusing organic residues and facilitating sustainable agricultural practices. In this study, we used the same model residues to produce OAs to enable meaningful comparisons among compost, digestate, and ferment. These three OAs contained different microbial communities. Compost had higher bacterial but lower fungal alpha diversity than ferment and digestate. Compost-associated microbes were more prevalent in the soil than ferment- and digestate-associated microbes. More than 80% of the bacterial ASVs and fungal OTUs from the compost were detected 3 months after incorporation into the soil. However, the addition of compost had less influence on the resulting soil microbial biomass and community composition than the addition of ferment or digestate. Specific native soil microbes, members from Chloroflexi, Acidobacteria, and Mortierellomycota, were absent after ferment and digestate application. The addition of OAs increased the soil pH, particularly in the compost-amended soil, whereas the addition of digestate enhanced the concentrations of dissolved organic carbon (DOC) and available nutrients (such as ammonium and potassium). These physicochemical variables were key factors that influenced soil microbial communities. This study furthers our understanding of the effective recycling of organic resources for the development of sustainable soils.

Choice of resolution by functional trait or taxonomy affects allometric scaling in soil food webs.

Belowground organisms often display a shift in their mass-abundance scaling relationships due to environmental factors such as soil chemistry and atmospheric deposition. Here we present new empirical data that show strong differences in allometric scaling according to whether the resolution at the local scale is based on a taxonomic or a functional classification, while only slight differences arise according to soil environmental conditions. For the first time, isometry (an inverse 1:1 proportion) is recognized in mass-abundance relationships, providing a functional signal for constant biomass distribution in soil biota regardless of discrete trophic levels. Our findings are in contrast to those from aquatic ecosystems, in that higher trophic levels in soil biota are not a direct function of increasing body mass.

Producing organic amendments: Physicochemical changes in biowaste used in anaerobic digestion, composting, and fermentation.

Organic amendments (OAs) produced via composting, anaerobic digestion, or lactic acid fermentation, can be used to replenish soil carbon. Not all OAs production technologies preserve C and nutrients in the same way. In this study, we compared the influence of these technologies (i.e., treatments) on C and nutrient preservation and OAs chemical composition after production. We produced compost, digestate, and lactic-acid fermentation product using the same biowaste-resembling model substrate using three reactors under laboratory conditions. We compared the chemical conversions and end-products using mass balances over C, N, and P. Overall results show that losses are minimal under reducing production conditions. Fermentation and digestion conserved 99% and 64% of C; and 93% and 100% of N, respectively. While compost conservation of nutrients was limited to 25% of C and 38% of N. Digestate had the highest concentrations of C, N, and P in the water-soluble phase, enabling their accessibility for soil microbes. Concentrations in the fermentation product were one order of magnitude lower but still higher than in compost. The treatments also influence the final availability of C, N, and P, which could potentially improve the fertilising and soil-improving properties of produced OAs. Our results show that under reducing conditions, losses of C, N, and P can be decreased while increasing OAs applications in terms of sources for soil-microbial development.

Species composition of a soil invertebrate multi-species test system determines the level of ecotoxicity.

A soil multi-species, SMS, experimental test system consisting of the natural microbial community, five collembolan species and a predatory mite along with either Enchytraeus crypticus or the earthworm Eisenia fetida were exposed to α-cypermethrin. A comparison of the performance of these two types of SMSs is given to aid the development of a standard test system. E. fetida had a positive effect on the majority of the species, reducing the negative insecticide effect. E. fetida affected the species sensitivity and decreased the degradation of the insecticide due to the organic matter incorporation of earthworm food. After 8 weeks, the EC50 was 0.76 mg kg(-1) for enchytraeids and ranged between 2.7 and 18.9 mg kg(-1) for collembolans, more sensitive than previously observed with single species. Changes observed in the community structure and function illustrates the strength of a multi-species test system as an ecotoxicological tool compared to single species tests.