Quantification of soil fauna metabolites and dead mass as humification sources in forest soils

The analysis of publications on soil food webs (FWs) allowed calculation of the contents of soil fauna metabolites and dead mass, which can serve as materials for humification. Excreta production of FWmicrofauna reaches 570 kg/ha annually, but the liquid excreta of protozoa and nematodes compose about 25%. The soil fauna dead mass can be also maximally about 580 kg/ha per year. However, up to 70% of this material is a dead mass of bacteria, protozoa, and nematodes. The undecomposed forest floor (L) has low values of these metabolites in comparison with the raw humus organic layer (F + H). The mass of these metabolites is twice lower in Ah. Theoretical assessment of earthworms’ role in SOM formation shows that the SOM amount in fresh coprolites can be 1.4 to 4.5-fold higher than SOM in the bulk soil in dependence on food assimilation efficiency, the soil: litter ratio in the earthworms’ ration, and SOM quantity in the bulk soil. Excreta production varies from 0.2 to 1.9% of the total SOM pool annually, including 0.15–1.5% of excrements of arthropods and enchytraeidae, but the amount of arthropods’ dead mass comprises 0.2–0.4%. The calculated values of the SOM increase due to earthworms’ coprolites are of the same order (0.9–2.7% of SOM pool annually). These values of SOM-forming biota metabolites and dead mass are close to the experimental and simulated data on labile and stable SOM fractions decomposition in forest soils (about 2% annually). Therefore, these biota’s products can play a role to restock SOM decrease due to mineralization.