Abstract:

Aims Nematodes are considered as an important part of the soil food web, and their community characteristics are an effective indicator of soil health and ecosystem restoration. The accurate measurement of soil nematode communities is necessary to better understand their ecological function. Historically, comparisons in nematode morphology has been used to understand nematode community characteristics. In recent years, the use of high-throughput sequencing (HTS) methods has become more popular. However, relatively little is known about how these two methods compare when analyzing soil nematode communities.
Methods Here, we used morphological identification and HTS methods to simultaneously analyze soil nematode abundance, community composition and structure, and ecological indexes, under different vegetation restoration approaches (cropland, naturally restored grassland, Caragana korshinskiiplantation and Medicago sativaartificial grassland) in the mountain area of southern Ningxia in the Loess Plateau region.
Result We found that morphological identification is a more accurate method to determine the absolute abundance of soil nematodes, while HTS can only obtain relative abundance data. In our study, the morphological method showed higher abundance of soil nematodes in the sites under vegetation restoration, especially in the naturally restored grassland and C. korshinskiiplantation. The HTS method, on the other hand, detected more nematode genera (42 genera belonging to 3 classes, 4 orders, and 26 families) than morphological method (27 genera belonging to 2 classes, 3 orders, and 18 families). However, only 15 genera were simultaneously identified with both methods, because the HTS method detected more plant-parasitic nematode genera (22) but fewer genera of bacterial-feeding nematodes and omnivores-predators than the morphological method. One major result indicated by both methods showed that the relative abundance of microbial-feeding nematodes greatly decreased, while those of plant parasites and omnivores-predators substantially increased, in all the sites under vegetation restoration when compared with nematodes in the farmland. This was especially the case in the naturally restored grassland and C. korshinskiiplantation, accompanied with the increases of maturity index (MI) and plant-parasitic index (PPI) and a decrease in the Wasilewska index (WI). When compared with the morphological method, the HTS method could detect more abundant and diverse plant parasites. Therefore, more significant differences were found in the composition, structure and ecological indexes of soil nematode communities when the HTS method was applied.
Conclusion Overall, the characteristics of soil nematode communities and their response patterns to vegetation restoration highly depended on the applied methodology, which greatly influences the understanding and evaluation of how vegetation restoration impacts the soil ecosystem.

Key words: morphological identification, high-throughput sequencing, soil nematodes, community structure, vegetation restoration