Depth-stratified soil sampling for assessing nematode communities

Abstract

This study assessed the importance of stratified soil sampling on the detection (and therefore the distribution) of nematode communities and the differentiation of ecosystems by collecting stratified soil samples at intervals of 10 cm and non-stratified samples from 0 to 30 cm in two soil management systems (no-tillage and conventional tillage) and in a native forest fragment. The nematode frequency and prominence values were obtained after extraction by successive screening operations, sugar floatation clarification and the identification of nematodes to the genus level. The nematode communities were compared two-by-two based on Sorensen's community coefficient (CC) and the percentage similarity (PS). Relative abundances of functional guilds were subjected to a principal component analysis (PCA) and classified in dendrograms. Thirty-two edaphic nematode genera were found, and the nematode communities sampled on a non-stratified basis in the soil profile exhibited a high level of similarity because they could not be accurately characterized. Genera with low abundances were not detected. In the stratified samples, we were able to classify and group the nematodes present at different depths, mainly from 0 to 10 cm. Stratified soil sampling allowed a more accurate characterization and greater differentiation of nematode communities, identifying taxa that occurred at lower abundance levels, irrespective of frequency. Key words: Bioindicators. Free-living nematodes. Nematofauna. Similarity. Vertical distribution. ResumoCom o objetivo de avaliar a importância da amostragem estratificada de solos na detecção (assim como na distribuição) de comunidades de nematoides e na diferenciação de ecossistemas, amostras de solo estratificadas em intervalos de 10 cm e não estratificadas de 0 a 30 cm foram coletadas em dois sistemas de prepare do solo (plantio direto e preparo convencional), e em um fragmento de floresta nativa. Após extração por peneiramento sucessivo, clarificação por flotação em sacarose e identificação dos nematoides até nível de gênero, a frequência e proeminência dos nematoides foram obtidas. As comunidades de nematoides foram comparadas duas a duas, baseadas no Coeficiente de comunidade de Sorensen e na Similaridade percentual (PS). Abundâncias relativas das guildas funcionais foram submetidas à Análise de componentes principais (PCA) e classificadas em dendrogramas. Trinta e dois gêneros de nematoides edáficos foram encontrados e as comunidades de nematoides amostradas de forma não estratificada no perfil do solo apresentaram um maior nível de similaridade entre si, pois não foram corretamente caracterizadas e os gêneros com baixa abundância não foram detectados. Nas amostras estratificadas, foi possível classificar e agrupar os nematoides presentes em diferentes profundidades, principalmente

Spatial impacts of a multi-individual grave on microbial and microfaunal communities and soil biogeochemistry

“…Within the grave, there was an overall reduction in nematode abundance and richness with depth. Previous studies have reported that approximately 70% of nematodes exist in the top 20 cm of soil and their distributions are associated with available food sources [85,86]. Our findings of elevated abundances at 30‒35 cm, in conjunction with high variation in samples at those depths, is likely due to elevated bacterial and fungal abundances in these areas.…”

“…With few exceptions [84–86], most field studies of nematodes focus on a single depth range, usually within the top 30 cm of the soil profile [38,47,49,52,53,56,87]. Our study compared multiple depths, and revealed that abundance, richness, and diversity decreased with depth both within and outside the grave.…”

Soil nematode functional diversity, successional patterns, and indicator taxa associated with vertebrate decomposition hotspots

“…We focused on the upper layers of soil because it has been demonstrated that approximately 70% of nematodes exist in the top 20 cm of soil. Nematode community composition at a local scale is most commonly associated with available food sources, both horizontally and vertically [28,47,48]. Therefore, we hypothesized that the highly enriched interface soils and deeper soils might harbor unique nematode community assemblages and/or successional patterns.…”

“…Thus, nematode community diversity and successional patterns have been shown to be sensitive indicators of soil enrichment and disturbance in agricultural systems [31][32][33][34][35][36][37][38][39][40][41][42][43] and composting processes [44,45]. Many field studies of nematodes focus on the upper 30 cm of soil, where the majority of free-living nematodes reside [24,31,[35][36][37][38][39][40][41]43,[46][47][48][49]. Vertical and horizontal distributions of soil nematodes are most commonly driven by food source location [47,48]; nematode density, particularly those of bacterivores, correlates with areas enriched in soil organic carbon (SOC), and therefore higher densities of bacterial biomass [28].…”

“…Many field studies of nematodes focus on the upper 30 cm of soil, where the majority of free-living nematodes reside [24,31,[35][36][37][38][39][40][41]43,[46][47][48][49]. Vertical and horizontal distributions of soil nematodes are most commonly driven by food source location [47,48]; nematode density, particularly those of bacterivores, correlates with areas enriched in soil organic carbon (SOC), and therefore higher densities of bacterial biomass [28].…”