Changes in soil free-living nematode communities and their trophic composition along a climatic gradient

Ambiguity exists concerning the effects of climate on soil nematode-community composition. In this study, we examined the free-living nematode communities in soil along a climatic gradient representing humid-Mediterranean, Mediterranean, semi-arid, and arid climate types. The relationships between abiotic soil characteristics (organic carbon, soil moisture (SM), water-holding capacity) and nematode parameters, such as abundance, trophic group composition, and diversity indices, were explored in the context of climate and seasonality. Nematode abundance was lowest at the arid site. At the humid Mediterranean and Mediterranean locations, nematode abundance reached its peak in winter, while at the semi-arid and arid sites, an almost opposite trend was observed, with lowest abundances in winter, presumably due to a nutrient washout from the soil profile during the rainy season. On the trophic level, one trophic group demonstrated a positive correlation with SM and one trophic group demonstrated a negative one at each location, while the other two groups remained constant. Fungi-feeding nematodes were found to be unaffected by SM at the humid-Mediterranean and Mediterranean locations, while at the semi-arid and arid sites their proportion increased in correlation with decreasing SM. Bacteria-feeders increased with SM at the arid site, were unaffected at the semi-arid location, and decreased with SM at the humid-Mediterranean and Mediterranean sites. Plant-parasites were associated with SM only at the humid-Mediterranean site. Omnivores-predators were positively affected by SM at the two middle locations, staying constant at the humid-Mediterranean and arid sites. These findings point to the strong linkage existing between nematode trophic behavior and climatic factors, demonstrating distinctive communal fingerprints for each climate type.

Profiling soil free-living nematodes in the Namib Desert, Namibia

Functional structure and diversity of soil free-living nematodes in a desert environment depend on plant gender and sampling site.The objective of this study was to compare the composition,abundance and tropic group of soil free-living nematodes in the upper 0–10 cm soil layer under the male and female Acanthosicyos horridus Welw.ex Hook.f.plants and in the inter-shrub open areas(control)in the Namib Desert,Namibia in April 2015.Soil moisture,organic matter(OM)and pH was also analyzed.Free-living nematodes were extracted from 100 g soil using the Baermann funnel procedure,and total number of nematodes was counted under a microscope.Community composition and diversity of soil free-living nematodes were analyzed using 18S rDNA sequences.Results indicated that a total of 67 groups,including 64 species,2 genera and 1 family were identified.Feeding behavior of 58 species were identified as follows:15 bacteria-feeding species,12 fungi-feeding species,10 plant-parasite species,5 omnivorous-predator species,8 animal-parasite species,5 invertebrate-parasite species and 3 non-free-living nematodes,known as marine species.Moreover,soil free-living nematodes were found to be affected by sampling locations and plant gender,and community composition and density of these nematodes were strongly influenced by soil OM content.Result confirmed that spatial location and plant cover were main factors influencing the diversity of soil free-living nematodes.Moreover,molecular tools were found to be very useful in defining the richness of soil non-free-living nematodes.In conclusion,the results elucidated the importance of biotic variables in determining the composition and abundance of soil free-living nematodes in the Namib Desert,Namibia.

Free-living nematode community structure and distribution within vineyard soil aggregates under conventional and organic management practices

Soil biota play a crucial role in soil ecosystem stability, promoting organic matter decomposition and nutrient cycling. Compared to conventional farming,organic farming is known to improve soil properties such as aggregation. Despite the importance of soil microbial communities in soil biogeochemical processes, our knowledge of their dynamics is rudimentary, especially under different agricultural management practices. Here we studied the effects of vineyard management practices(conventional and organic) and soil aggregate fractions(micro-, meso-, and macroaggregates) on free-living soil nematodes.The abundance, diversity, and ecological indices, such as the Wasilewska index and trophic diversity, of free-living soil nematodes were determined. We found that the abundance of free-living soil nematodes was increased by organic farming. In addition, plant parasites were found to increase in macroaggregates in the organic plot, which may be attributed to the weeds present due to no-tillage and no herbicides. Nematode family network connectivity increased in complexity with increasing aggregate size, highlighting the importance of the interplay between nematodes and soil inter-aggregate pore size and connectivity.