A meta-analysis of nematode community composition across soil aggregates: Implications for soil carbon dynamics

Abstract

Soil aggregation is a key contributor to soil carbon (C) accrual and stabilization. Yet, little is known regarding how soil food web structure shifts across aggregate size and how this in turn could significantly influence soil C stabilization within aggregates. In order to cohesively understand the link between nematodes and soil C, we conducted a meta-analysis consisting of 98 observations from 11 papers to quantitatively assess how nematode community composition changes by aggregate size. Due to the small sample size of this meta-analysis publication bias was assessed through the use of funnel plots. Additionally, to prevent certain studies from skewing results, studies that were outside of the 95% Confidence Interval (CI) pooled effect were excluded from the meta-analysis. The investigation of the relationship between nematode community composition and total soil organic C across aggregate size revealed no distinct difference between the summary response ratios for total nematode abundance and all trophic groups. This finding indicates that nematode composition did not differentiate by aggregates size. Soil organic carbon (SOC) values varied by aggregate size, where microaggregates (<0.25 mm) had 117% greater SOC values relative to the macro-aggregates (>2 mm). Additionally, mid-sized aggregates (0.25 mm–2 mm) had 115% greater SOC relative to macro-aggregates. SOC and total nematode abundance were negatively correlated in aggregate sizes of 0.25-2 mm (Pearson's r = −0.38, p < 0.03) and >2 mm (Pearson's r = −0.42, p < 0.04). The relationship between SOC and bacterivore to fungivore abundance ratio (Pearson's r = 0.52, p < 0.005). These results indicate that nematode community composition, especially where bacterivores are in greater abundance, is associated with SOC stabilization in mid-sized aggregates.