Nematodes require space: The relationship between nematode community assemblage and soil carbon across varying aggregate fractions

Abstract

Soil aggregates are critical for soil carbon (C) sequestration and serve as a habitat for microorganisms, including free-living nematodes. Yet, the interactions between nematode community composition and soil C cycling across aggregate fractions is rarely assessed. The objectives of this study were to 1) determine how soil type alters nematode community dispersal across aggregate fractions, 2) understand how soil type may alter the relationship between nematode communities and labile C pools, and 3) assess the impact that tillage intensity has on nematode community assemblage across aggregate fractions. Soil cores were taken at two identical long-term trials located in Ohio (silt loam vs. clay). Each trial compared two different tillage intensities (chisel till vs. no-till). Soils were fractionated into three aggregate fractions (>2000 μm, 2000–250 μm, and <250 μm). For each fraction, nematode communities were identified to feeding group and permanganate oxidizable carbon (POXC) was measured. Results indicated that silt loam soils had greater bacterivore nematodes in the >250 μm aggregate fraction (p < 0.05) and relatively lower predator-omnivore nematode proportions when compared to clay soils. Tillage did not have a significant effect on nematode feeding groups. Correlation analyses revealed that predator-omnivore nematodes and POXC were positively correlated in clay soils, but only in the largest aggregate fraction (p < 0.05). Bacterivore nematodes were positively correlated with POXC in clay soils but negatively correlated in silt loam soils (p < 0.05). These findings reveal that predator-prey dynamics likely drive soil C accumulation in larger sized aggregates. Moreover, shifts in nematode community composition by soil type demonstrates how inherent properties influence soil food web structure and ultimately, soil C cycling.