Advancing soil nematode research: molecular, morphological and stable isotope analyses

by Simin Wang
Doctoral thesis
Date of Examination:2024-09-26
Date of issue:2025-09-16
Advisor:Prof. Dr. Stefan Scheu
Referee:Prof. Dr. Stefan Scheu
Referee:Prof. Dr. Christoph Bleidorn
Persistent Address: http://dx.doi.org/10.53846/goediss-11502

 

 

Files in this item

Name:PhD dissertation_Simin Wang (21568520).pdf
Size:3.63Mb
Format:PDF

The following license files are associated with this item:

Abstract

English

The overarching aim of this dissertation was to explore the impact of environmental variances on soil nematode communities, their trophic interactions and their ecological roles by integrating traditional morphological methods with advanced molecular techniques and innovative isotopic analyses. In chapter 2, HTS data from a soil nematode biodiversity experiment was used to explore standardized HTS data processing procedures, from gene database selection to the analysis of compositional data. Overall, this study highlights the importance of comparing and selecting taxonomic reference databases before data analyses, and provides solid evidence for the similarity and comparability between OTU- and ASV-based nematode studies. Further, the results highlight the potential weakness of rarefaction-based and clr-transformation-based methods. We recommend future studies to use ASV and that both the taxonomic reference databases and normalization strategies are carefully tested and selected before analyzing the data. In chapter 3, morphological methods were used to link nematode functional groups to specific energy channels, providing insights into how environmental conditions affect soil nematode dynamics in a 16-year-old oil palm plantation. The study revealed that microbial channels, particularly the fungal channel, are more prominent in aboveground suspended soils, while plant and bacterial channels dominate belowground compartments. These findings are crucial for understanding the ecological dynamics within oil palm plantations and demonstrate how environmental factors influence the roles of different nematode trophic groups in soil processes. In chapter 4, soil and litter samples were collected from forests of different ages (30-40 and 70-80 years old) as a case study, using both compound-specific isotope analysis (CSIA) of amino acids and morphological methods to analyze the trophic niches of soil nematodes. The CSIA analysis showed a consistent dependence of nematodes on bacterial and plant-derived resources across different forest ages and layers, with bacterial resources being particularly dominant. This study demonstrates the effectiveness of CSIA in providing precise dietary insights, supporting its use in future soil food web and nutrient cycling studies. Integrating CSIA with traditional methods enhances our understanding of soil nematode ecology, offering a comprehensive perspective on their roles in nutrient dynamics and ecosystem functioning.
Keywords: Soil nematodes; High-throughput sequencing (HTS); Morphological analysis; Compound-specific isotope analysis (CSIA); Trophic interactions; Soil food webs
 
Statistik