Linking microbial co-occurrences to soil ecological processes across a woodland-grassland ecotone

Abstract

Ecotones between distinct ecosystems have been the focus of many studies as theyoffer valuable insights into key drivers of community structure and ecological processes that underpin function. While previous studies have examined a wide range ofabove-ground parameters in ecotones, soil microbial communities have received little attention. Here we investigated spatial patterns, composition, and co-occurrencesof archaea, bacteria, and fungi, and their relationships with soil ecological processesacross a woodland-grassland ecotone. Geostatistical kriging and network analysisrevealed that the community structure and spatial patterns of soil microbiota variedconsiderably between three habitat components across the ecotone. Woodlandsamples had significantly higher diversity of archaea while the grassland samples hadsignificantly higher diversity of bacteria. Microbial co-occurrences reflected differences in soil properties and ecological processes. While microbial networks weredominated by bacterial nodes, different ecological processes were linked to specificmicrobial guilds. For example, soil phosphorus and phosphatase activity formed thelargest clusters in their respective networks, and two lignolytic enzymes formedjoined clusters. Bacterial ammonia oxidizers were dominant over archaeal oxidizersand showed a significant association (p < 0.001) with potential nitrification (PNR),with the PNR subnetwork being dominated by Betaproteobacteria. The top ten keystone taxa comprised six bacterial and four fungal OTUs, with Random ForestAnalysis revealing soil carbon and nitrogen as the determinants of the abundance ofkeystone taxa. Our results highlight the importance of assessing interkingdom associations in soil microbial networks. Overall, this study shows how ecotones can beused as a model to delineate microbial structural patterns and ecological processesacross adjoining land-uses within a landscape.