Towards a standardised protocol for estimating nematode-based indices in ecological studies: extraction step

Summary Extraction is a critical step in the analysis of nematode communities for ecological studies, yet standardised protocols for estimating nematode-based indices (NBIs) remain underdeveloped. This study evaluates the effects of different extraction techniques, soil sample sizes, storage durations and extraction times on nematode community recovery and estimation of NBIs across three soil types. Three extraction methods: Whitehead & Hemming trays (WT), sucrose centrifugation (SC), and a combined approach (WT+SC), were compared. Our results indicate that WT underestimated total nematode counts, particularly omnivores and herbivores, leading to lower maturity (MI) and structure (SI) indices but higher basal index (BI) values compared to SC and WT+SC. Increased soil sample size (10-200 g) did not significantly affect NBIs but influenced nematode density estimates, with 200 g of soil yielding the most reliable results. Storage duration at 4°C significantly altered nematode community composition, with notable changes in most NBIs and nematode trophic group estimations, highlighting the need for prompt sample processing. Extending extraction time beyond 72 h increased herbivore recovery with no effect on other trophic groups or NBIs. Our findings suggest a combined WT+SC with 72 h extraction as an optimised protocol for extraction nematodes from 200 g freshly collected soil samples. These insights contribute to the development of standardised protocols for nematode extraction and NBI estimation, enhancing the reliability of nematodes as bioindicators in ecological studies.