Vertical distribution of soil free-living nematode in a playa habitat in the North-Western Negev desert, Israel

In order to investigate the vertical distribution of soil nematode community under a playa area in the Nizzana inter-sand dune area in the north-western Negev Desert of Israel, soil samples were collected from 0 – 10, 10 – 20, 20 – 30, 30 – 40, and 40 – 50 cm depths in the playa and loessial plain area (as control) during the dry and wet seasons. Each of soil samples was determined for soil moisture, organic matter concentration, electrical conductivity, and nematode community structure and biodiversity. The results revealed that soil moisture, organic matter, electrical conductivity, total nematode abundance and trophic groups were significantly influenced by sampling positions (P < 0.0001) and depths (P < 0.05) and significant interaction effect of position and depth (P < 0.05) was also found. Total number of nematodes in the playa area ranged from 1 to 15 individuals per 100 g dry soil, whereas they ranged from 60 to 631 individuals per 100 g dry soil in the loessial plain area. The greatest nematode number was found in 0 – 10 cm soil depth and the lowest nematode number was found in 40 – 50 cm soil depth. Total number of nematodes, bacterivores, fungivores, plant parasites and omnivores-predators were significantly (P < 0.05) greater in the loessial plain area than that in the playa area in all sampling depths under the dry and wet seasons. Total thirteen genera were found in the playa area, with Acrobeloides as the dominant genus, whereas there were fifty-five genera, with Acrobeles as the dominant genus in the loessial plain area. Nematode ecological indices, such as fungivores/bacterivores ratio (F/B), nematode channel ratio (NCR), trophic diversity (T), Shannon Index (H’), genus dominance (λ), species richness (SR), maturity index (MI), modified maturity index (MMI), Enrichment Index (EI) and Structure Index (SI) were significantly (P < 0.01) differentiated between sampling locations. As conclusion, soil free-living nematode inhabited mostly the upper soil layers (0 – 20 cm) and the number of nematode had gradually decreasing trend with soil depths increasing in the playa area. Moreover, each soil layer had a little nematode abundance and community diversity in the playa area in contrast to loessial plain area during the dry and wet seasons. Sampling sites and depths significantly effected on soil properties, nematode abundance and trophic groups, but nematode ecological indices were affected only by sampling sites.