Arbuscular mycorrhizal fungi reshape the stability and complexity of micro-food webs in the shrubland soils of a dryland ecosystem

Abstract

Soil micro-food webs constitute critical biological networks sustaining terrestrial ecosystem functionality. The structural dynamics (including stability and complexity) in soil micro-food webs are important for regulating nutrient flow within the soil, thereby influencing the nutrient supply to plants. Xerophytic shrubs in dryland ecosystems frequently establish obligate symbiotic associations with arbuscular mycorrhizal fungi (AMF), forming critical ecological partnerships for nutrient acquisition. However, critical knowledge gaps persist in understanding how AMF modulate micro-food web architecture and regulate stability-complexity dynamics in dryland soils, particularly regarding their spatial-temporal variability and hydrological dependencies. We established a controlled culture system for the xerophytic shrub Artemisia ordosica and AMF to investigate the effects of AMF on the stability and complexity of soil micro-food webs. AMF inoculation and soil water content (SWC) treatments significantly altered the community structure of bacteria, protists, and nematodes in both rhizosphere and bulk soils, as well as fungi in rhizosphere soils, but showed limited impact on fungal communities in bulk soils. AMF enhanced rhizosphere stability by strengthening fungal-bacterial synergies (+63 % positive interaction), and AMF regulated the soil micro-food web structure through the “bottom-up” effect (significant alterations among lower trophic levels influencing higher trophic levels). Conversely, extreme drought shifted AMF's role to “top-down” effect (opposite to “bottom-up” effect) destabilizing rhizosphere networks via amplified protist-nematode antagonism (+235 % negative interactions). The regulation of soil micro-food web stability and complexity by AMF under well-watered and extreme drought conditions is complex in bulk soils. This study identified critical hydrological thresholds (3 % SWC) governing AMF functional transitions, advancing mechanistic insights into mycorrhizal regulation of nutrient cascades in arid soils. Although our experimental system may amplify AMF functions compared to natural conditions, these findings advance mechanistic understanding of trophic interactions in dryland soils.