ReviewLarge-scale patterns of distribution and diversity of terrestrial nematodes

- Soil nematode had large scale distribution patterns on a global scale.
- The highest soil nematode mean abundance was recorded in temperate coniferous forest.
- Soil nematode richness and maturity index were significantly related to latitude.
- Climate factors and vegetation types had major effects on soil nematode abundance.

Latitude, climate and vegetation type are key factors in the distribution of soil nematodes. The diversity of most aboveground organisms increases with decreasing latitude, but the macro-ecological diversity and geographic distribution patterns of belowground animals have been poorly studied. The large-scale geographic distribution patterns of soil nematodes were examined in terms of their abundance and their driving forces, with a view towards ascertaining whether the large-scale patterns (LSP) of distribution and diversity of soil nematodes were driven by latitude, climate and vegetation type. A literature review representing multiple vegetation types across latitudinal gradients was conducted, and information was gathered pertaining to soil nematodes throughout the globe. Different databases, such as Google Scholar, Web of Sciences, Scopus and PubMed, were searched to collect data published in English-language journals. A correlational analysis between soil nematode diversity and latitude, mean annual precipitation and mean annual temperature was performed. The present review also compared the abundance and genus of soil nematodes among different vegetation types. The LSP of the soil nematodes was unimodal, and a higher nematode abundance was recorded at latitudes between 30 and 55°. A significant correlation was observed between the latitude and species richness index, whereas latitude explained 65.9% of the variation in the species richness index across plots. Nematode abundance showed a distinct peak at a mean annual temperature of approximately 8 °C, but no significant correlation was found between the nematode abundance and mean annual precipitation. The highest mean value of soil nematode abundance was recorded in temperate coniferous forests, followed by tropical forest, grassland, temperate broadleaf forest, crop field and garden, desert and polar vegetation types. The mature index of soil nematodes was negatively correlated with latitude. A redundancy analysis (RDA) showed that the composition of the trophic group of the soil was greatly influenced by latitude (LA) and mean annual precipitation (MAP). The number of the soil nematode genera was found to be highest in temperate broadleaf forests, followed by tropical forest, grassland, temperate coniferous forest, crop field and garden, desert and polar vegetation types. Soil nematodes exhibited large-scale distribution patterns along latitudes on a global scale as a result of hydrothermal conditions, plant growth and human activities.