Effects of microhabitats and soil conditions on structuring patterns of nematode communities in Japanese cedar (Cryptomeria japonica) plantation forests under temperate climate conditions

The effect of biotic factors impacted by abiotic conditions on nematode communities is not fully understood in forest ecosystems. Monoculture forests with low understory diversity would provide an ideal model system to investigate the relationship between nematode community structure and environmental factors in forest ecosystems. The aim of this study was to clarify the determinant environmental factors shaping community structures of soil nematodes in Japanese cedar (Cryptomeria japonica) forests. Nematodes collected from litter and soil samples were morphologically identified at the family or genus level and divided into trophic groups. Nematodes were discriminated into a total of 40 (including 2 unique taxa) and 52 (including 14 unique taxa) taxa in litter and soil samples, respectively. Variation in microhabitat substrates created contrasting nematode assemblages between litter and soil samples. Moreover, nematodes identified from litter habitats were a subset of those from soil samples. Bacterivorous and fungivorous nematodes were present in high proportions in both sample types. Herbivorous nematodes were the third most abundant trophic group in soil samples, but were rare in litter samples. The nematode community structure in soils was significantly ordinated by water, C, N, hyphae, and soil pH. The pH is most likely to affect ecological function of soil nematodes indirectly by altering microbial biomass. Our results showed that microhabitat substrates, that is, soil and litter, have a crucial effect on nematode assemblage patterns in temperate coniferous forests. Moreover, soil nematode assemblages were diversified due to the high spatial heterogeneity of proximate soil environments.