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

Abstract

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 humidMediterranean 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 humidMediterranean 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 humidMediterranean 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

“…Moreover, their interactions with other biota are not limited to feeding on bacteria, fungi, plant cells and omnivores. They also feed on other nematodes, heterotrophic protists and arthropod hosts (Yeates et al, 1993;Yeates and King, 1997;Levi et al, 2012). The activity, density and diversity of soil free-living nematodes in natural environments were found to be strongly influenced by soil physical-chemical characteristics and food resources (Pen-Mouratov et al, 2004;Fitoussi et al, 2016).…”

Phylogenetic Relationships of Insect-Associated Free-Living Rhabditid Nematodes From Eastern Mediterranean Region of Turkey

“…They indirectly contribute to nitrogen mineralization by grazing on decomposer microbes, excreting ammonium, and immobilizing nitrogen in live biomass (Ferris et al, 1998;Neher, 2001). Due to their high occurrence, diversity, different tropic levels, and sensitivity to abiotic alterations free-living nematodes also contribute as bioindicators to environmental pollution and soil quality studies (Levi et al, 2012). Their high phenotypic plasticity among populations reduces the number of diagnostic characters in rhabditid nematode groups.…”

Dynamic biospeckle analysis, a new tool for the fast screening of plant nematicide selectivity

“…Soil health cannot be measured directly and frequent use has been made of biological indices such as composition of nematode communities [28, 68]. Significant spatial [69] and temporal variation, for example due to climatic conditions [70], and the lack of direct knowledge of their feeding habits [3], limits the use of univariate indices in the field [71]. Because current methods lack the ability to monitor live activity, several components with a net significant effect on soil function, remain underemphasized [72].…”

“…There is potential, therefore, to develop diagnostic tools based on biospeckle principles to complement metagenomic approaches which lack the ability to measure a live response. Given that site conditions can change rapidly between sampling, current techniques that infer treatment effects by comparing relative nematode abundances, require a range of other variables, such as soil moisture and temperature to be considered [70, 73, 74]. By using live organisms and observing effects in real-time, however, BSPIM allows the bioactivity of different trophic or functional groups sampled in the field to be monitored under controlled laboratory conditions.…”