# Influence of _Eisenia fetida_ on the Nematode Populations during Vermicomposting Process
## 3 Results and Discussion  
In our treatment, 23 nematode genera were identified. Bacterial-feeders represented 80.7% of total nematofauna including 11 genera (Figure 1A). Fungal-feeders represented 11.0% of nematode abundance (five genera) (Figure 1B). Plant-parasitic nematodes (PPN) represented 0.2% of the total density, and three genera were identified (_Merlinius, Parathylenchus_, _Pratylentchus_). Notably, PPN presence was only detected on the initial day of composting. Omnivores (5.3%) were represented by _Eudorylianus_ and _Dorylaimus_ (Figure 1C) and Predators (2.8%) by _Mononchoides_ and _Prisionchus_ genera (Figure 1D). The total nematode density was 1.46-fold higher in the treatments with _Eisenia fetida_ than in the non-inoculated treatment. Figure 1: Cont. Molecular metabarcoding has been proposed as a promising method to rapidly measure the community composition based on the genetic identification of species [25; 26] The morphometric method for identifying nematode species revealed a higher count compared to the molecular metabarcoding technique. In the examined substrate samples, approximately 10,000 nematode individuals were discovered, predominantly bacteriores and fungivores, encompassing larval stages. This conclusion aligns with the findings of [PERSON] and [PERSON] [27], who remarked that fully identifying all nematodes in a soil sample to determine the total species count is nearly impractical. The discrepancy or absence of a specific nematode species uncovered through molecular analysis compared to classical taxonomy's morphometric identification can be attributed to this limitation. Although metabarcoding is a highly promising technique, it has its drawbacks, including sensitivity of the results to marker choice and the fact that reference databases are incomplete [28; 29]. Next-generation sequencing reads (NGS) have been assigned at different taxa levels: family, genera, species and even strains or isolates. Examples of the reads assignment are presented in Figure 2.  
Figure 1: Abundance of the nematode community at the genera level per 200 cc compost sample: bacteriores (**A**), fungivores (**B**), omnivores (**C**) and predators (**D**) on the 30 th, 60 th and the 90 th day of composting (n = 3). Figure 2: Krona graph representing the nematode community abundance estimated by NGS sequencing of pulled (n = 3) specimens in three compost variants without earthworms: C1 (**A**), C2 (**B**), C3 (**C**) and three compost variants with _Eisenia fetida_: C4 (**D**), C5 (**E**), and C6 (**F**) on the 30 th day of composite. The morphological approach of nematodes allows fast and relatively inexpensive identification to the genus level but identification to the species level requires the involvement of experts for every family of detected nematodes and appropriate nematode museum collections. Moreover, the identification of specimens is limited to this sex and developmental stage for which morphological keys have been developed. To overcome this limitation, we identified the nematodes present in compost sampled by metabarcoding. This approach is sex- and stage-insensitive but limited by the presence of molecular marker sequences in the appropriate databases, marker sequence intragenic variability and the \"barcoding gap\"--differences in similarity between sequences belonging to the same and other species. Moreover, in some genera (_Bursaphelenchus_, _Ektaphelenchus_, _Panagrellus_, _Panagrolainus_) there are inconsistencies between nematode species, included in the World Database of Nematodes and TaxId of NCBI (Table 1). For _Bursaphelenchus_ World Database of Nematodes listen 43, while in GenBank there are sequence records for 92 species. To a lesser extent, this also applies to _Ektaphelenchus_, _Panagrellus_, _Panagrolainus_. For other genera there is consistency between World Database of Nematodes and TaxId of NCBI, but number of species with sequenced markers (18S and 28S rDNA) varies from 0% (_Demaniella_, _Protorlabditis_) to 93% (_Prisionchus_).