Abstract. Microbes play an essential role in soil functioning including biogeochemical
cycling and soil aggregate formation. Yet, a major challenge is to link
microbes to higher trophic levels and assess consequences for soil
functioning. Here, we aimed to assess how microbial consumers modify
microbial community composition (PLFA markers), as well as C dynamics
(microbial C use, SOC concentration and CO2 emission) and soil
aggregation. We rebuilt two simplified soil consumer–prey systems: a
bacterial-based system comprising amoebae (Acanthamoeba castellanii) feeding on a microbial
community dominated by the free-living bacterium Pseudomonas fluorescens and a fungal-based system
comprising collembolans (Heteromurus nitidus) grazing on a microbial community dominated by the
saprotrophic fungus Chaetomium globosum. The amoeba A. castellanii did not affect microbial biomass and
composition, but it enhanced the formation of soil aggregates and tended to
reduce their stability. Presumably, the dominance of P. fluorescens, able to produce
antibiotic toxins in response to the attack by A. castellanii, was the main cause of the
unchanged microbial community composition, and the release of bacterial
extracellular compounds, such as long-chained
polymeric substances or proteases, in reaction to predation was responsible for the changes in soil
aggregation as a side effect. In the fungal system, collembolans significantly
modified microbial community composition via consumptive and non-consumptive
effects including the transport of microbes on the body surface. As
expected, fungal biomass promoted soil aggregation and was reduced in the
presence of H. nitidus. Remarkably, we also found an unexpected contribution of
changes in bacterial community composition to soil aggregation. In both the
bacterial and fungal systems, bacterial and fungal communities mainly
consumed C from soil organic matter (rather than the litter added).
Increased fungal biomass was associated with an increased capture of C from
added litter, and the presence of collembolans levelled off this effect.
Neither amoebae nor collembolans altered SOC concentrations and CO2
production. Overall, the results demonstrated that trophic interactions are
important for achieving a mechanistic understanding of biological
contributions to soil aggregation and may occur without major changes in C
dynamics and with or without changes in the composition of the microbial
community.
Conservation Tillage Impact on Topsoil and Deep Soil Aggregation and Aggregate Associated Carbon Fractions and Microbial Community Composition in Subtropical India: A Review
