Insights into the interlinkages between rhizosphere soil extracellular enzymes and microbiome assemblages across soil profiles in grasslands

Abstract

Understanding the correlations between the turfgrass rhizosphere soil (RS) microbial community assembly and soil extracellular enzymes (EEs) across soil profiles can contribute to enhancing the soil C pool and improving urban grassland ecosystem services. This study collected rhizosphere soil from non-native Poa pratensis (Poa L.) and native Carex leucochlora (Carex L.) at depths of 0–40 cm to investigate soil properties, EEs, and microbial communities. Compared to Poa, Carex significantly increased RS soil properties (i.e., organic carbon (SOC), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and available NPK), C-, and N- acquisition (acq) enzymes, and soil ecosystem multifunction at 0–40 cm soil depths. Variable selection-dominated RS bacterial and fungal assemblages were enhanced in Poa and increased with soil depth, while homogenizing dispersal-dominated RS microbiome assemblages were enhanced in Carex and increased with soil depth. Among soil enzymes, the existence of C-acq enzymes were tie to more taxa to sustain the natural connectivity of RS microbial networks. Random forest analysis revealed that taxa of Actinobacteria (Mycobacterium, Gaiella, and Hyphomicrobium) and Nitrospirae (Nitrospira) played a key role in mediating C-acq enzymes, with Carex recruiting more bacterial taxa involved in amino acid and carbohydrate metabolism. Structural equation modeling further indicated the crucial role of the RS bacterial assemblage in regulating Actinobacteria, Nitrospirae, and Proteobacteria, highlighting their significance in C-acq enzymes, SOC, MBC, and MBN. This study demonstrated that Carex was more likely to increase soil ecosystem service, and concluded that the RS microbial community assemblages could stimulate bacterial taxa to strengthen the closely associations between soil C-acq enzymes and SOC sequestration.