Abstract
High latitude ecosystems are characterized by cold soils and long winters, with much of their biogeochemistry directly or indirectly controlled by temperature. Climate warming has led to an expansion of shrubby plant communities across tussock tundra, but whether these clear aboveground shifts correspond to changes in the microbial community belowground remains less certain. Using bromodeoxyuridine to label growing cells, we evaluated how total and actively growing bacterial communities varied throughout a year and following 22 years of passive summer warming. We found that changes in total and actively growing bacterial community structures were correlated with edaphic factors and time point sampled, but were unaffected by warming. The aboveground plant community had become more shrub-dominated with warming at this site, and so our results indicate that belowground bacterial communities did not track changes in the aboveground plant community. As such, studies that have used space-for-time methods to predict how increased shrub cover has altered bacterial communities may not be representative of how the microbial community will be affected by in situ changes in the plant community as the Arctic continues to warm.
Highlights
Climate change is altering the Arctic with unprecedented speed; the Arctic is warming at a rate two to six times the global average (Cohen et al, 2014)
We found bacterial community structure was unaffected by 22 years of passive summer warming despite greenhouse treatment increasing woody plant dominance
Microbial community composition has been observed to be temporally dynamic at other tundra sites (Wallenstein et al, 2007; McMahon et al, 2011; Vorskovaet al., 2019), and—in contrast to a previous study (Deslippe et al, 2012)—our results indicate that bacterial communities from this long-term warming study are temporally dynamic
Summary
Climate change is altering the Arctic with unprecedented speed; the Arctic is warming at a rate two to six times the global average (Cohen et al, 2014) This has led to permafrost thaw and a deepening active layer within Arctic soils (Yi et al, 2018; Plaza et al, 2019). Arctic tundra systems are experiencing an increase in both overall plant productivity and shrub dominance (Tape et al, 2006; Wang et al, 2019)—a “greening of the Arctic” (Jia et al, 2003). These coupled abovegroundbelowground changes in response to warming are expected to significantly alter tundra biogeochemical cycling and C balance. The greater shade provided by shrubs can reduce summer soil
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