Temperature changes affect multi-trophic interactions among pines, mycorrhizal fungi, and soil nematodes in a microcosm experiment

Abstract

Nematodes serve a key role in soil nutrient cycling by eating bacterial cells and fungal hyphae. However, little is known about how temperature changes affect multi-trophic interactions among host trees, root-associating fungi, and nematodes. The aim of this study was to identify abiotic and/or biotic factors that affect soil nematode communities. We constructed a pot microcosm with sandy soils from a coastal Pinus thunbergii forest. The soil-filled pots were incubated for 8 months at 20, 25, or 30 °C with or without pine seedlings. In the pots with seedlings, we measured the percentages of black, white, and brown ectomycorrhizal (ECM) formations on roots. Nematodes retrieved from the soils were morphologically identified to genus and differentiated by both trophic and community structures. The occurrence of ECM formation ranged from 85.7%–91.9%. Black ECM roots were significantly dominant at 30 °C (47.0 %), whereas white ones were significantly dominant at 20 °C (43.0 %) and 25 °C (53.0 %). The number of nematodes at 25 and 30 °C was significantly greater than that at 20 °C irrespective of the presence or absence of seedlings. In terms of trophic compositions, the relative abundance of fungivorous nematodes significantly increased from 10.4 % at 20 °C to 27.5 % at 25 °C to 44.6 % at 30 °C in the presence of pine seedlings. A non-metric multidimensional scaling scatter plot showed that the nematode communities clustered significantly among temperature treatments. Structural equation modeling indicated that nematode trophic compositions were directly regulated by temperature and the presence of pine seedlings. Our findings suggest that temperature has some cascading effects on the formation of nematode communities, and pine seedlings and associating ECM fungi contributed synergistically to the formation of their communities.