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Crop production is strongly impacted by soil nitrogen supply, which is regulated by soil micro-food webs consisting of nematodes, protists, fungi and bacteria. However, responses of soil micro-food webs to fertilization at the aggregate scale and their relationships with soil nitrogen supply and crop yield remain unclear. To address these knowledge gaps, we investigated soils subjected to typical fertilization treatments in a long-term field experiment, which included: no fertilizer control (CK); synthetic fertilizers (NPK); partial synthetic nitrogen replacement with pig slurry (OMNPK) or crop straw (RSDNPK) and incorporating biochar with synthetic fertilizers (BCNPK). The composition of different biological groups was changed significantly by fertilization, with bacteria under RSDNPK being more responsive than other groups. The co-occurrence network of the soil micro-food web had more edges in microaggregates than those in large and small macroaggregates due to the significantly higher nodal degree of bacteria and fungi. On average, 76 % of the topologically important (TI) taxa in the networks were bacteria. In modules where nematodes and protists were present, 8 %-100 % of them were attributed to TI taxa while the ratio for bacteria was 3 %-7 %. Specific assemblages of functionally important (FI) taxa covering all tested biological groups at the aggregate scale were positively associated with soil labile nitrogen, related enzymes and crop yield. Random forest regression further indicates the high importance of these FI taxa to crop yield. However, less than 20 % of them were attributed to TI taxa of the networks. In summary, distinct assemblages of taxa covering multiple trophic levels regulate network topology and soil nitrogen supply + crop yield, which provides insights for targeted manipulation of soil micro-food webs through knowledge-based fertilization to harness the biological potential of cropland soils.

Agriculture in the boreal and Arctic regions is perceived as marginal, low intensity and inadequate to satisfy the needs of local communities, but another perspective is that northern agriculture has untapped potential to increase the local supply of food and even contribute to the global food system. Policies across northern jurisdictions target the expansion and intensification of agriculture, contextualized for the diverse social settings and market foci in the north. However, the rapid pace of climate change means that traditional methods of adapting cropping systems and developing infrastructure and regulations for this region cannot keep up with climate change impacts. Moreover, the anticipated conversion of northern cold-climate natural lands to agriculture risks a loss of up to 76% of the carbon stored in vegetation and soils, leading to further environmental impacts. The sustainable development of northern agriculture requires local solutions supported by locally relevant policies. There is an obvious need for the rapid development of a transdisciplinary, cross-jurisdictional, long-term knowledge development, and dissemination program to best serve food needs and an agricultural economy in the boreal and Arctic regions while minimizing the risks to global climate, northern ecosystems and communities.

Collembola display a variety of feeding habits, and prey on many types of food at different trophic levels in the soil. In most cases, their feeding selections are widely varied. In the interest of the food preferences of E. proxima, we attempted to confirm how the Collembola utilize food when feeding on carrion (unusual sources). Four different soil animals (with different stable isotope values and increasing trophic levels) were used to examine whether collembolans can use dead insects as a food resource in specific manners, depending on food preference. Our results demonstrated that the food preference of a collembolan changed significantly after feeding on insects with different feeding habits for 60 days. We found that stable isotope values (δ13C) of Entomobrya proxima approached those of the food sources. A large proportion of the diet (more than 50%) should directly consist of insect body parts, with the remainder consisting of indirectly used, mixed microorganisms naturally growing on animal food, such as fungi (Rhizopus sp., Alternaria sp., Penicillium sp., and Aspergillus sp.) and bacteria (Bacillus sp1. and Bacillus sp2.). Based on this research, the food preference of collembolans is more focused on carcasses (dead insect bodies) than microorganisms during the animal-food decomposition process.

Parameters characterizing the structure of the decomposer food web, biomass of the soil microflora (bacteria and fungi) and soil micro-, meso- and macrofauna were studied at 14 non-reclaimed 1- 41-year-old post-mining sites near the town of Sokolov (Czech Republic). These observations on the decomposer food webs were compared with knowledge of vegetation and soil microstructure development from previous studies. The amount of carbon entering the food web increased with succession age in a similar way as the total amount of C in food web biomass and the number of functional groups in the food web. Connectance did not show any significant changes with succession age, however. In early stages of the succession, the bacterial channel dominated the food web. Later on, in shrub-dominated stands, the fungal channel took over. Even later, in the forest stage, the bacterial channel prevailed again. The best predictor of fungal bacterial ratio is thickness of fermentation layer. We argue that these changes correspond with changes in topsoil microstructure driven by a combination of plant organic matter input and engineering effects of earthworms. In early stages, soil is alkaline, and a discontinuous litter layer on the soil surface promotes bacterial biomass growth, so the bacterial food web channel can dominate. Litter accumulation on the soil surface supports the development of the fungal channel. In older stages, earthworms arrive, mix litter into the mineral soil and form an organo-mineral topsoil, which is beneficial for bacteria and enhances the bacterial food web channel.

The diversity of life is one of the most striking aspects of our planet; hence knowing how many species inhabit Earth is among the most fundamental questions in science. Yet the answer to this question remains enigmatic, as efforts to sample the world's biodiversity to date have been limited and thus have precluded direct quantification of global species richness, and because indirect estimates rely on assumptions that have proven highly controversial. Here we show that the higher taxonomic classification of species (i.e., the assignment of species to phylum, class, order, family, and genus) follows a consistent and predictable pattern from which the total number of species in a taxonomic group can be estimated. This approach was validated against well-known taxa, and when applied to all domains of life, it predicts ~8.7 million (± 1.3 million SE) eukaryotic species globally, of which ~2.2 million (± 0.18 million SE) are marine. In spite of 250 years of taxonomic classification and over 1.2 million species already catalogued in a central database, our results suggest that some 86% of existing species on Earth and 91% of species in the ocean still await description. Renewed interest in further exploration and taxonomy is required if this significant gap in our knowledge of life on Earth is to be closed.

We adapted a direct count method for obtaining counts of active protozoa that was not overly time consuming. Soil samples from an agricultural field were examined at 1- to 3-day intervals three times through the year. The three sampling periods represented different weather conditions. At each sampling event, fresh soil samples were extracted upon return to the laboratory for protozoa. These were enumerated at the microscope without prior culture, in soil–water suspension dilutions. We describe a procedure that allowed all samples to be processed in a few hours. Our results suggest there is good reproducibility and agreement between samples collected on the same day. Our data resolve differences between days as soil conditions changed slowly with drying or wetting. This procedure is suitable for describing species active at the time of sampling. Unlike the ‘most probable number’ procedure that relies on cultivable species, it is less prone to enumerating excysting individuals, and it provides better resolution between sampling dates, with a relatively low number of samples. [ABSTRACT FROM AUTHOR]