Decline of soil microbial diversity does not influence the resistance and resilience of key soil microbial functional groups following a model disturbance

Abstract

Analysing the consequences of the decrease in biodiversity for ecosystem functioning and stability has been a major concern in ecology. However, the impact of decline in soil microbial diversity on ecosystem sustainability remains largely unknown. This has been assessed for decomposition, which is insured by a large proportion of the soil microbial community, but not for more specialized and less diverse microbial groups. We determined the impact of a decrease in soil microbial diversity on the stability (i.e. resistance and resilience following disturbance) of two more specialized bacterial functional groups: denitrifiers and nitrite oxidizers. Soil microbial diversity was reduced using serial dilutions of a suspension obtained from a non-sterile soil that led to loss of species with low cell abundance, inoculation of microcosms of the same sterile soil with these serial dilutions, and subsequent incubation to enable establishment of similar cell abundances between treatments. The structure, cell abundance and activity of denitrifying and nitrite-oxidizing communities were characterized after incubation. Increasing dilution led to a progressive decrease in community diversity as assessed by the number of denaturating gradient gel electrophoresis (DGGE) bands, while community functioning was not impaired when cell abundance recovered after incubation. The microcosms were then subjected to a model disturbance: heating to 42 degrees C for 24 h. Abundance, structure and activity of each community were measured 3 h after completion of the disturbance to assess resistance, and after incubation of microcosms for 1 month to assess resilience. Resistance and resilience to the disturbance differed between the two communities, nitrite oxidizers being more affected. However, reducing the diversity of the two microbial functional groups did not impair either their resistance or their resilience following the disturbance. These results demonstrate the low sensitivity of the resistance and resilience of both microbial groups to diversity decline provided that cell abundance is similar between treatments.

Effects of aboveground grazing on coupling among nitrifier activity, abundance and community structure

“…In contrast, this was not observed for the community structure, except for U-G treatment after 24 months. This shows that similar nitrifier activity can be insured by AOB communities differing in their community structure, which is consistent with the high functional redundancy of soil bacterial communities including nitrifiers (Wertz et al, 2006(Wertz et al, , 2007. Investigating the composition of the active nitrifier community using mRNA rather than the genetic community structure could partly explain the decoupling observed between nitrifier activity and community structure.…”

Despite strong seasonal responses, soil microbial consortia are more resilient to long-term changes in rainfall than overlying grassland

“…There is speculation that the broad taxonomic distribution of functional traits within microbial communities may confer functional robustness to losses of taxa and changes in composition (Giller et al, 1997;Wolters et al, 2000;Griffiths et al, 2001;Wertz et al, 2007). Intriguingly, this study shows that microbial community composition itself can be robust both to changing climate and to associated changes in plant production and species composition.…”

Mechanisms determining the fate of dispersed bacterial communities in new environments

“…As the main assumption made by the neutral model is the functional equivalence of taxa (Hubbell, 2001), no compositional changes, but rapid functional adaptations of dispersed populations, should occur when they arrive in a new habitat, as functional plasticity is expected to be high. This corresponds to the adjustment scenario of Comte and del Giorgio (2011) and is supported by studies that have shown that microbial communities can functionally adapt to different environments even without drastic changes in composition, and that microbial communities of different composition can perform equally owing to their functional redundancy (Wohl et al, 2004;Wertz et al, 2007;Comte and del Giorgio, 2010;Werner et al, 2011).…”