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.
Highlights
Grassland ecosystems occupy approximately 41% of the Earth's land surface (Reynolds et al, 2007), and play an important role in global biogeochemical, hydrological, and energy cycles (Huang et al, 2018)
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
This litter type decomposes relatively quickly on the ground (Bonanomi et al, 2019), but is highly flammable and most of it remains in the plant tussock, a condition that promotes the occurrence of fire events in this grassland (Incerti et al, 2013)
Summary
Grassland ecosystems occupy approximately 41% of the Earth's land surface (Reynolds et al, 2007), and play an important role in global biogeochemical, hydrological, and energy cycles (Huang et al, 2018). SE is a phenomenon in which grasses and herbaceous vegetation are replaced by woody shrubs (Sankaran et al, 2004). SE is a form of land cover change that is widespread in arid and semi-arid grassland ecosystems (Eldridge et al, 2011). This phenomenon has been shown, to significantly alter the landscape, microclimate, and above- and belowground biological processes (Dong et al, 2014). Shrub encroachment (SE) is a phenomenon in which grasses and herbaceous vegetation are replaced by woody shrubs. The progressive spread of shrubs represents a form of land cover change that is widespread in arid and semi-arid grassland ecosystems. We used high-throughput sequencing, coupled with soil chemical analyses and litter using 13C CPMAS NMR spectroscopy
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