Long-term in situ permafrost thaw effects on bacterial communities and potential aerobic respiration

Abstract

The decomposition of large stocks of soil organic carbon in thawing permafrost might depend on more than climate change-induced temperature increases: indirect effects of thawing via altered bacterial community structure (BCS) or rooting patterns are largely unexplored. We used a 10-year in situ permafrost thaw experiment and aerobic incubations to investigate alterations in BCS and potential respiration at different depths, and the extent to which they are related with each other and with root density. Active layer and permafrost BCS strongly differed, and the BCS in formerly frozen soils (below the natural thawfront) converged under induced deep thaw to strongly resemble the active layer BCS, possibly as a result of colonization by overlying microorganisms. Overall, respiration rates decreased with depth and soils showed lower potential respiration when subjected to deeper thaw, which we attributed to gradual labile carbon pool depletion. Despite deeper rooting under induced deep thaw, root density measurements did not improve soil chemistry-based models of potential respiration. However, BCS explained an additional unique portion of variation in respiration, particularly when accounting for differences in organic matter content. Our results suggest that by measuring bacterial community composition, we can improve both our understanding and the modeling of the permafrost carbon feedback.

Permafrost thawing exhibits a greater influence on bacterial richness and community structure than permafrost age in Arctic permafrost soils

“…Thus the changed nutrients may explain the significant influence of thawing status on the community structure and assembly processes. The community structure change due to permafrost thawing has also been proposed to be due to the colonization of microorganisms in active layer (Monteux et al, 2018), which coincides with the increased bacterial richness observed here (Fig. 2a).…”

“…In contrast, permafrost thawing substantially activates a diverse range of oligotrophic and copiotrophic bacteria, and enriches carbohydrate transporter and metabolism-related genes (Schostag et al, 2019). This leads to an increased bacterial richness and converged community metabolic functions, and the soil carbon being dominated by aliphatic carbon resulted from microbial transformation (Deng et al, 2015;Mackelprang et al, 2011;Monteux et al, 2018;Schostag et al, 2019).…”

Potential feedback mediated by soil microbiome response to warming in a glacier forefield

“…The relative abundance between the same order of active and total microbes was quite different, and several OTUs of active microbes exhibited low abundances in the DNA‐derived microbial communities, including Enterobacteriales and Clostridiales, which might dismiss the activity of active microbes. Furthermore, the shifts in the clusters of the active microbial communities were similar to previous shifts in the total microbial community structure under long‐term warming and changes in metagenome functional genes under short‐term warming (DeAngelis et al, ; Mackelprang et al, ; Monteux et al, ).…”

“…Studies on the grassland of the Great Plains of the United States and the Tibetan Plateau have indicated a declining trend or nonsignificant change in the capacity of decomposing recalcitrant carbon, which appeared to be associated with stabilizing the topsoil carbon stock of the whole ecosystem (Yue et al, ; Zhou et al, ). The change in the microbial community structure was the result of warming (DeAngelis et al, ; Monteux et al, ), which in turn affected the feedback on climate change (Bardgett et al, ; Zhou et al, ). Considering the temperature effect, RNA‐derived microbial communities could be applied to explain heat feedback by influencing the CO 2 ‐C release rate (De Vrieze et al, ).…”

“…Soil DNA contains different microbial metabolic states, including active, growing, dormant, and decreased DNA (Blazewicz et al, 2013). Compared with RNA, DNA might have a lag phase prior to changing with external disturbances to maintain a stable structure and reserve potential function (Monteux et al, 2018). The total microbial communities might have a diverse function pool that enables it to cope with interference (Blazewicz et al, 2013), and this function could be a life strategy under longterm interference conditions (de Vries & Shade, 2013).…”