Effects of climatic and edaphic conditions on structuring patterns of soil nematode communities in Japanese cedar (Cryptomeria japonica) plantations

Strong associations exist between organism and soil functions in forest ecosystems at large spatial scales; however, it is unclear the community patterns of soil nematodes. Artificial monoculture forests with poor understory vegetation would provide an ideal model system to characterize the relationship between nematode community structures and local habitat conditions. This study aimed to understand how climate and soil properties influence the community structure of soil nematodes in artificial Japanese cedar (Cryptomeria japonica) plantations. The richness, abundance, and community structure of the nematodes were assessed using soils (20 cm in depth) collected from eight 1 ha C. japonica plantations (40–60 years), which were distributed between 24°N and 42°N, with cool temperate, temperate, and subtropical zones in summer. The soil nematode aggregates were identified using a high throughput sequencing of the MiSeq system. The richness of amplicon sequence variances of nematodes revealed a significant unimodal pattern with latitude, with the greatest richness observed at 33°N. In contrast, nematode abundance showed a significant U-shaped pattern with latitude and was lower at mid-latitudes. Nematode community structures in subtropical zones clearly differed from those in the temperate and cool temperate zones. Among the environmental factors measured, mean annual temperature, soil pH, and C content accounted for the greatest variations in nematode communities. These results indicate that nematode richness and abundance displayed opposite patterns along latitudinal gradients. Moreover, the interrelationship between climate and soil conditions was identified as the best predictor of the community structure of soil nematodes in the monocultural C. japonica forest ecosystems. This study provided a useful view of belowground biodiversity for evaluating forest health in Asian coniferous plantations.