Abstract. Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species, Lotus corniculatus (Fabaceae) and Plantago lanceolata (Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.

The genus Coomansus Jairajpuri & Khan, 1977 encompasses more than 30 species occuring in various habitats. The Coomansus zschokkei-group, characterized by a posterior position of the dorsal tooth, includes 11 species spread in the northern hemisphere: Europe (3 species), Asia (Far East, Korea, Japan – 8 species), North America (Costa Rica and USA – 1 species), which are reported from subalpine habitats and forests, but also freshwater lakes. So far, one species (C. zschokkei (Menzel, 1914)) was recorded from Bulgaria (Iliev and Ilieva 2019). During this study three undescribed species have been found from mountain areas of Bulgaria. These three closely related Coomansus species were studied using an integrative approach. Based on the dimensions of the buccal capsule and the posterior position of the dorsal tooth they are similar to C. zschokkei, C. cobbi (Eroshenko, 1975), C. mucronatus (Eroshenko, 1975) and C. simenensis (Kreis, 1924), but differ from them by a number of characters such as buccal capsule length, tail length, and lateral piece shape. Coomansus cf. menzeli Loof & Viniszewska-Slipińska, 1993 recovered from moss around birch tree at the Central Balkan Mountain is a new geographical record for Bulgaria. Phylogenetic analyses based on 18S and D2-D3 expansion domains of rRNA genes have been performed for the first time for members of Coomansus zschokkei-group. In both phylogenetic reconstructions, all Coomansus species with the exception of C. gerlachei (De Man, 1904) formed a monophyletic group with very high bootstrap support values. Speciation within the group seems to be related to glaciation and post-glaciation events in mountain areas.

The riparian zones represent habitats of high and specific biodiversity; however, historically they have been subject to intensive exploitation and most of them are drastically changed. Predatory nematodes are widespread terrestrial organisms and play an important role in biological regulation of litter/soil communities. Some preliminary results on the mononchid fauna in riparian habitats in South Bulgaria are presented. Thirty-four samples were collected from 29 localities with various vegetation types in three districts: Sofia, Smolyan and Burgas. Multiple core soil samples (3 per site) were collected from each habitat (15×15 m sampling site or along the river bank) around the roots of the dominant tree at a depth of 40–60 cm and from litter. The most intensively sampled plant tree was Salix spp. (11 samples) followed by Fraxinus spp. (8), Alnus glutinosa (L.) Gaertn. (6) and Ulmus spp. (3). Nematodes were isolated from 200 g of soil (by decanting and sieving method) and 10 g of litter (Baerman funnel method), fixed, dehydrated and mounted on permanent slides. More than 90% of all soil and litter samples contained at least one mononchid genus. Six genera: Prionchulus (Cobb, 1916) Wu and Hoeppli, 1929, Clarkus Jairajpuri, 1970, Mononchus Bastian, 1865 (fam. Mononchidae), Mylonchulus Cobb, 1916 (fam. Mylonchulidae), Miconchus Andrassy, 1958 and Anatonchus Cobb, 1916 (fam. Anatonchidae) were recovered. Prionchulus spp. prevailed in litter, occurring in half of the collected samples, while Mylonchulus spp. were most common in soil samples (35%). Representatives of Clarkus and rarely Mylonchulus occurred in both litter and soil. The highest diversity of mononchids (4 genera) was detected in the rhizosphere of Ulmus laevis Pall. along a small river in Strandzha Mt. Further morphological and molecular studies on populations and species identification are envisaged.

Soil fungi are key component of soil biota having an important role in many ecological processes. As pathogens, decomposers and plant mutualists they can affect plant and soil health in agro-ecosystems significantly. The impact of crop management practices on soil fungal communities is diverse and still poorly studied. The lack of knowledge is mainly related to their hidden life mode, high phenotypic diversity, the great heterogeneity of soil microhabitats, difficulty for culturing and species identification. Collecting data with high accuracy to detect effects relevant to ecosystem management is an ongoing challenge for soil ecological studies and biomonitoring. However, the combination of DNA-based identification methods and Next Generation Sequencing technology was recognized as a powerful tool to evaluate biodiversity in environmental samples, especially soil biodiversity. In the frame of the National Research Program "Healthy Foods for a Strong Bio-Economy and Quality of Life", soil microbiome diversity (fungi, prokaryotes and archaea) will be used as indicator for assessing soil and plant health, and ecosystem services in several agricultural ecosystems. Four crop types (apple, lavender, rose and pea) located in southern Bulgaria, and managed by conventional and organic farming have been selected. Two general objectives related to soil biodiversity study were envisaged: to examine the impact of cropping systems on microbiome structural and functional diversity, and to propose management measures and agronomic practices improving soil and plant health. to examine the impact of cropping systems on microbiome structural and functional diversity, and to propose management measures and agronomic practices improving soil and plant health. Here we present some preliminary results on soil fungal communities evaluated by using amplicon DNA sequencing of the internal transcribed spacer 2 (ITS2) rDNA region. Multiple core soil samples were collected from 18 sampling plots in June 2019. Fungal diversity and community structure were evaluated at different taxonomic levels. The most common and abundant taxa at all sites were Fusarium Link 1809, Solicoccozyma X.Z.Liu, F.Y.Bai, M.Groenew. & Boekhout 2015, Cladosporium Link 1816, Alternaria Nees ex Wallroth 1816, and Mortierella E.Coemans 1863. The multivariate statistics (PCA) comparing the overall microbial composition revealed loose clusters linked to crops and localities. The study provides a new comprehensive overview of soil fungal communities (composition and diversity) from Bulgarian agro-ecosystems using high-throughput DNA sequencing.

Nematodes represent one of the largest phyla in the animal kingdom and are a key component of the soil microfauna (organisms with body width <0.2 mm). Being a widespread and diverse group, they display a wide range of adaptations and lifestyle traits. Their functional role in soil food-webs is mostly related to their feeding type. The majority of terrestrial nematodes feed on plant roots, bacteria and fungi, while a small group of plant associated species spend part or their whole life cycle in roots. Some plant-feeding species are known as important pests that can parasitize various crops causing adverse effects on yield and production quality. Their effective management requires accurate detection and identification. In the frame of the National Research Program "Healthy Foods for a Strong Bio-Economy and Quality of Life", selected groups of soil nematodes are used as bioindicators for assessing soil and plant health, and ecosystem services in several agricultural ecosystems. Nematode communities from four crop types (pea, apple, lavender and rose) in southern Bulgaria managed by conventional and organic farming were sampled and investigated. Here we present some preliminary results on pea, lavender and rose associated nematode diversity. Multiple core samples from 18 sampling plots were collected in June 2019. Nematodes were isolated from 200 g of soil by decanting and sieving method, fixed, dehydrated and mounted on permanent slides. Overall, over 60 genera belonging to five trophic groups were identified. Approximately half of the nematode genera found are obligatory plant- and plant/fungus feeders. Parasitic nematodes were represented by 12 genera, some of which include important pests known to cause severe damages on crops e.g. Meloidogyne Goeldi, 1889, Pratylenchus Filipjev, 1934, Pratylenchoides Winslow, 1958 and Tylenchorhynchus Cobb, 1913.