The effect of forest edges on soil nematode community structures between broadleaf secondary forest and coniferous plantation

Habitat edges between two forest types significantly affect the community structure and dynamics of soil organisms Nematodes are a major group of soil microfauna and the most abundant animals on Earth. This study aimed to determine the edge effects of two forest types on soil nematode community composition. We hypothesized that nematode diversity and abundance would be greater in forest edges due to increased heterogeneity of aboveground litter and belowground root traits at the boundary between two forest types, as well as microclimatic variation, enhanced resource inputs, higher plant diversity, and unique soil moisture dynamics characteristic of edge environments. The soil was collected from two adjacent forests, a broadleaf Quercus serrata forest and a coniferous Cryptomeria japonica plantation, with the zone where the two forests transition into one another being referred to as the "forest edge”. Soil nematodes were morphologically identified at the genus/family level and examined for both community structure and trophic composition. Our results showed that there was a significant positive correlation between the relative abundance of herbivorous nematodes and the physical distance from the broadleaf forest to the C. japonica plantation. The diameter of coniferous C. japonica fine roots were greater than those of broadleaf Q. serrata, suggesting that herbivorous nematodes had easily access to edible resources leading to an increase their populations. Moreover, the nematode community structures had a spatial autocorrelation within a 32 m range, their community structures changed significantly from broadleaf forests to C. japonica plantations and that soil pH and C/N significantly influenced the structuring of nematode communities. This study showed that nematode taxonomic and trophic compositions can be influenced by tree root traits within a range of several tens of meters around forest edges facing different forest types. Our results highlighted that forest edges enhance soil nematode taxonomic turnover.