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

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 mu m, 2000-250 mu m, and <250 mu m). 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 mu m 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 predatoromnivore 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.

Automated summary

Soil aggregates play a crucial role in soil carbon sequestration and provide a habitat for microorganisms, including nematodes. Yet, little is known about the interactions between nematode community composition and soil carbon cycling across different aggregate fractions. This study aimed to investigate the effects of soil type and tillage intensity on nematode community distribution and their relationship with labile carbon pools. The results showed that soil type influenced the distribution of nematode feeding groups across different aggregate fractions, while tillage intensity had no significant effect. The correlation analyses revealed that predator-omnivore nematodes and permanganate oxidizable carbon were positively correlated in clay soils but not in silt loam soils. These findings highlight the importance of predator-prey dynamics and soil type in soil carbon accumulation and cycling.