Depth-dependent influence of different land-use systems on bacterial biogeography

Abstract

Despite progress in understanding microbial biogeography of surface soils, few studies have investigated depth-dependent distributions of terrestrial microorganisms in subsoils. We leveraged high-throughput sequencing of 16S rRNA genes obtained from soils collected from the RARE: Charitable Research Reserve (Cambridge, ON, Canada) to assess the influence of depth on bacterial communities across various land-use types. Although bacterial communities were strongly influenced by depth across all sites, the magnitude of this influence was variable and demonstrated that land-use attributes also played a significant role in shaping soil bacterial communities. Soil pH exhibited a large gradient across samples and strongly influenced shifts in bacterial communities with depth and across different land-use systems, especially considering that physicochemical conditions showed generally consistent trends with depth. We observed significant (p ≤ 0.001) and strongly correlated taxa with depth and pH, with a strong predominance of positively depth-correlated OTUs without cultured representatives. These findings highlight the importance of depth in soil biogeographical surveys and that subsurface soils harbour understudied bacterial members with potentially unique and important functions in deeper soil horizons that remain to be characterized.

Toward more robust plant‐soil feedback research

“…This is not a trivial assumption: Mounting evidence indicates soil biota compositions vary widely across small spatial scales due to dispersal processes, soil physicochemical properties, soil water content, and other factors (Monard et al 2016, Zhang et al 2016, Ping et al 2017, Seuradge et al 2017). This is not a trivial assumption: Mounting evidence indicates soil biota compositions vary widely across small spatial scales due to dispersal processes, soil physicochemical properties, soil water content, and other factors (Monard et al 2016, Zhang et al 2016, Ping et al 2017, Seuradge et al 2017).…”

“…Combining soil samples by NAS and species prevented Teste et al from confirming step 1. Soil microbe compositions can vary widely across small spatial scales (Monard et al 2016, Zhang et al 2016, Ping et al 2017, Seuradge et al 2017, Wang et al 2017, so some sampled microbial species may have occurred near just one or a few field plants. Even microbes occurring near a single plant would presumably be distributed to 20 conspecific glasshouse pots and ≥150 NAS mixture pots (Appendix S1: Fig.…”

“…In order to conclude that phytometers grown in unconditioned field soil measure PSFs occurring in nature, it must be assumed that field plants causally determine which soil biota occur where. This is not a trivial assumption: Mounting evidence indicates soil biota compositions vary widely across small spatial scales due to dispersal processes, soil physicochemical properties, soil water content, and other factors (Monard et al 2016, Zhang et al 2016, Ping et al 2017, Seuradge et al 2017, Wang et al 2017). Insofar as stochastic or abiotic factors determine which soil biota occur where, phytometers will be misleading indicators of PSFs.…”

Contrasting biogeographic patterns of bacterial and archaeal diversity in the top- and subsoils of temperate grasslands

“…Declining carbon substrate availability with soil depth produces oligotrophic environment at depth, which may restrict bacterial activity and promote subsurface-dwelling groups capable of utilizing recalcitrant carbon sources (35, 36). Previous studies have shown that soil bacterial diversity is typically highest in the topsoil and decreases with soil depth (34, 37). However, the diversity or abundance of different bacterial phyla may decrease (36, 37), increase (38), or remain consistent (34) along soil profile.…”

“…Previous studies have shown that soil bacterial diversity is typically highest in the topsoil and decreases with soil depth (34, 37). However, the diversity or abundance of different bacterial phyla may decrease (36, 37), increase (38), or remain consistent (34) along soil profile. Compared with bacteria, soil archaeal diversity patterns are much less explored at depth.…”