Proximate grassland and shrub-encroached sites show dramatic restructuring of soil bacterial communities.

Xingjia Xiang,Sean M Gibbons,He Li,Haihua Shen,Haiyan Chu

doi:10.7717/peerj.7304

Abstract

BackgroundChanges in aboveground community composition and diversity following shrub encroachment have been studied extensively. Recently, shrub encroachment was associated with differences in belowground bacterial communities relative to non-encroached grassland sites hundreds of meters away. This spatial distance between grassland and shrub sites left open the question of how soil bacterial communities associated with different vegetation types might differ within the same plot location.MethodsWe examined soil bacterial communities between shrub-encroached and adjacent (one m apart) grassland soils in Chinese Inner Mongolian, using high-throughput sequencing method (Illumina, San Diego, CA, USA).ResultsShrub-encroached sites were associated with dramatic restructuring of soil bacterial community composition and predicted metabolic function, with significant increase in bacterial alpha-diversity. Moreover, bacterial phylogenic structures showed clustering in both shrub-encroached and grassland soils, suggesting that each vegetation type was associated with a unique and defined bacterial community by niche filtering. Finally, soil organic carbon (SOC) was the primary driver varied with shifts in soil bacterial community composition. The encroachment was associated with elevated SOC, suggesting that shrub-mediated shifts in SOC might be responsible for changes in belowground bacterial community.DiscussionThis study demonstrated that shrub-encroached soils were associated with dramatic restructuring of bacterial communities, suggesting that belowground bacterial communities appear to be sensitive indicators of vegetation type. Our study indicates that the increased shrub-encroached intensity in Inner Mongolia will likely trigger large-scale disruptions in both aboveground plant and belowground bacterial communities across the region.

Highlights

Increased cover, abundance and dominance of shrub species in grasslands have been widely reported, with 10–20% of arid and semiarid grassland area undergoing shrub encroachment across the world (Van Vegten, 1984; Jackson et al, 2002; Maestre et al, 2009)
Soil chemistry Compared to non-encroached grassland soils, shrub-encroached soils were associated with higher content of NO3, total nitrogen (TN), total carbon (TC), dissolved organic carbon (DOC), soil organic carbon (SOC), and total phosphorus (Table S1)
Bacterial operational taxonomic units (OTUs) richness was positively correlated with NO3, DOC, TC, TP, and SOC; Phylogenetic diversity (PD) was positively correlated with NO3, DOC, TC, and SOC; the Shannon index was positively correlated with NO3, TC, TP, and SOC; evenness was positively correlated with NO3, TN, TC, and SOC (Table 1)

Summary

Introduction

Abundance and dominance of shrub species in grasslands have been widely reported, with 10–20% of arid and semiarid grassland area undergoing shrub encroachment across the world (Van Vegten, 1984; Jackson et al, 2002; Maestre et al, 2009). Shrub encroachment was associated with differences in belowground bacterial communities relative to non-encroached grassland sites hundreds of meters away. Results: Shrub-encroached sites were associated with dramatic restructuring of soil bacterial community composition and predicted metabolic function, with significant increase in bacterial alpha-diversity. The encroachment was associated with elevated SOC, suggesting that shrub-mediated shifts in SOC might be responsible for changes in belowground bacterial community. Discussion: This study demonstrated that shrub-encroached soils were associated with dramatic restructuring of bacterial communities, suggesting that belowground bacterial communities appear to be sensitive indicators of vegetation type. Our study indicates that the increased shrub-encroached intensity in Inner Mongolia will likely trigger large-scale disruptions in both aboveground plant and belowground bacterial communities across the region

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Discussion

Conclusion