Distribution and community structure of soil nematodes in coastal Japanese pine forests were shaped by harsh environmental conditions

Abstract

Nematode community studies have been carried out in various forests for several decades. However, in forest ecosystems, the diversity of woody plant taxa with different plant species makes it difficult to determine factors regulating nematode communities. In this respect, monoculture forests in sandy coastal areas can be model systems for characterizing nematode communities because harsh environments limit plant growth and, consequently, soil nematodes. The purpose of this study was to characterize the community structure and spatial pattern of soil nematodes molecularly in coastal Pinus thunbergii forests. Nematodes were collected from two soil layers at each of four sites and subjected to DNA sequence analysis focusing on partial SSU rRNA. In total, 398 sequences were determined from 400 nematode specimens (50 nematodes per soil layer per site). These sequences formed 36, 37, 50, and 84 molecular operational taxonomic units (MOTUs) at identity levels of 97%, 98%, 99%, and 100%, respectively. The MOTUs at a 98% identity level corresponded to genera in nematode assemblages. The bacterivorous Acrobeloides (relative abundance, 20–25%), omnivorous Aporcelaimellus (15–20%), and bacterivorous Prismatolaimus (12–22%) were the dominant taxa that collectively accounted for 60% of all genera detected in the top (0–10 cm soil depth) and bottom (10–20 cm) soil layers. The rank abundance pattern was best explained by the Mandelbrot model being a few taxa with other many minor taxa. Nematode communities formed two clusters regardless of the physical distances between study sites. Cluster 1 was characterized by higher soil water content and cluster 2 was characterized by higher pH. These results suggest that nematode community structure of the coastal pine forest is simple, and are regulated by proximate abiotic factors such as water content and soil pH.