Abstract
Shrub encroachment (SE) is a phenomenon in which grasses and herbaceous vegetation are replaced by woody shrubs. Many previous studies have highlighted the effects of SE on soil respiration rates and nutrient storage, but little is known about impacts on soil microbiota. While previous work considered shrubs to be non-species specific or as a single intervening species, we selected an Ampelodemsos mauritanicus grassland and six coexisting shrubs (i.e. Pistacia lentiscus L., Juniperus phoenicea L., Myrtus communis L., Rosmarinus officinalis L., Olea europaea L., and Euphorbia dendroides L.) to investigate the effects of their encroachment on soil microbiota. We used high-throughput sequencing, coupled with soil chemical analyses and litter using 13C CPMAS NMR spectroscopy. Results showed a strong influence of shrub species on bacterial and fungal community diversity, species richness and overall community composition in the soil. Litter chemistry was dominated by O-alkyl-C, with the highest content in Ampelodesmos and E. dendroides, but richer of aromatic C in P. lentiscus and R. officinalis. Bacterial diversity was highest under J. phoenicea and E. dendroides, while lowest under R. officinalis and grassland. Conversely, fungal diversity was highest under O. europaea and E. dendroides, while lowest under M. communis and grassland. Moreover, soil C and N contents were highest under O. europaea, P. lentiscus and M. communis compared to the other shrub species. In addition, grassland and R. officinalis had the highest Fe content. Structural equation model (SEM) analysis ascertained that the shifts of bacterial and fungal community composition and diversity were closely related with the changes of litter and soil chemical properties. Our results suggest that the individual effect of each shrub on the grassland matrix depends mainly on the chemical properties of the shrub litter, which alters the chemical profile of the soil and, in cascade, shapes the associated microbiota.
•Shrub encroachment consists of replacing grasses and herbaceous vegetation by shrubs.•We assessed litter and soil chemistry, and microbiota by next-generation sequencing.•Litter chemistry varied among shrubs and affected differently soil chemicals.•Coexisting shrubs generate specific microbial signatures in the soil.•Fungi were more dependent on soil chemical characteristics than bacteria.