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

Samiran Banerjee,Peter H. Thrall,Andrew Bissett,Marcel G. A. van der Heijden,Alan E. Richardson

doi:10.1002/ece3.4346

Abstract

Ecotones between distinct ecosystems have been the focus of many studies as they offer valuable insights into key drivers of community structure and ecological processes that underpin function. While previous studies have examined a wide range of above‐ground parameters in ecotones, soil microbial communities have received little attention. Here we investigated spatial patterns, composition, and co‐occurrences of archaea, bacteria, and fungi, and their relationships with soil ecological processes across a woodland‐grassland ecotone. Geostatistical kriging and network analysis revealed that the community structure and spatial patterns of soil microbiota varied considerably between three habitat components across the ecotone. Woodland samples had significantly higher diversity of archaea while the grassland samples had significantly higher diversity of bacteria. Microbial co‐occurrences reflected differences in soil properties and ecological processes. While microbial networks were dominated by bacterial nodes, different ecological processes were linked to specific microbial guilds. For example, soil phosphorus and phosphatase activity formed the largest clusters in their respective networks, and two lignolytic enzymes formed joined clusters. Bacterial ammonia oxidizers were dominant over archaeal oxidizers and 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 Forest Analysis revealing soil carbon and nitrogen as the determinants of the abundance of keystone taxa. Our results highlight the importance of assessing interkingdom associations in soil microbial networks. Overall, this study shows how ecotones can be used as a model to delineate microbial structural patterns and ecological processes across adjoining land‐uses within a landscape.

Highlights

Ecotones between adjacent ecosystems or biomes that harbor contrasting plant communities represent useful areas for investigation, as they support unique ecological dynamics (Anadón, Sala, & Maestre, 2014; Archer & Predick, 2014)
A multifarious approach was used to address the following specific questions: (a) How do the spatial structure, composition, and co-occurrences of soil archaeal, bacterial, and fungal communities change across a woodland-grassland ecotone?; (b) How are ammonia oxidizing bacteria and archaea linked to potential nitrification across such ecotones?; (c) Is the composition of microbial networks related to soil properties and ecological processes?; and (d) Which soil properties drive the abundance of microbial keystone taxa across the woodland-grassland ecotone?
Quantitative PCR, high-throughput sequencing and network analysis, we demonstrated spatial patterns and co- occurrences of archaeal, bacterial, and fungal communities across a woodland-grassland ecotone

Summary

| INTRODUCTION

Ecotones between adjacent ecosystems or biomes that harbor contrasting plant communities represent useful areas for investigation, as they support unique ecological dynamics (Anadón, Sala, & Maestre, 2014; Archer & Predick, 2014). Ecotones encompass interactions occurring between adjoining systems and are useful because the local effects of shifts in vegetation can be explicitly assessed independently of the environmental variability that may occur over broader spatial scales (Gosz, 1993) Such areas can reveal the edge effect between two adjacent habitats (Lacasella, Gratton, & De Felici, 2015; Malmivaara-Lämsä et al, 2008; Murcia, 1995). A multifarious approach was used to address the following specific questions: (a) How do the spatial structure, composition, and co-occurrences of soil archaeal, bacterial, and fungal communities change across a woodland-grassland ecotone?; (b) How are ammonia oxidizing bacteria and archaea linked to potential nitrification across such ecotones?; (c) Is the composition of microbial networks related to soil properties and ecological processes?; and (d) Which soil properties drive the abundance of microbial keystone taxa across the woodland-grassland ecotone?

| MATERIALS AND METHODS

| DISCUSSION

Findings

| CONCLUSION