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Πέμπτη 11 Μαΐου 2017

Shifts in microbial trophic strategy explain different temperature sensitivity of CO 2 flux under constant and diurnally-varying temperature regimes

<span class="paragraphSection"><div class="boxTitle">Abstract</div>Understanding soil CO<sub>2</sub> flux temperature sensitivity (Q<sub>10</sub>) is critical for predicting ecosystem-level responses to climate change. Yet, the effects of warming on microbial CO<sub>2</sub> respiration still remain poorly understood under current Earth system models, partly as a result of thermal acclimation of organic matter decomposition. We conducted a 117-day incubation experiment under constant and diurnally-varying temperature treatments based on four forest soils varying in vegetation stand and soil horizon. Our results showed that Q<sub>10</sub> was greater under varying than constant temperature regimes. This distinction was most likely attributed to differences in the depletion of available carbon between constant-high and varying-high temperature treatments, resulting in significantly higher rates of heterotrophic respiration in the varying-high temperature regime. Based on 16S rRNA gene sequencing data using Illumina, the varying-high temperature regime harbored higher prokaryotic alpha-diversity, was more dominated by the copiotrophic strategists, and sustained a distinct community composition, in comparison to the constant-high treatment. We found a tightly coupled relationship between Q<sub>10</sub> and microbial trophic guilds: the copiotrophic prokaryotes responded positively with high Q<sub>10</sub> values, while the oligotrophs showed a negative response. Effects of vegetation stand and soil horizon consistently supported that the copiotrophic vs. oligotrophic strategists determine the thermal sensitivity of CO<sub>2</sub> flux. Our observations suggest that incorporating prokaryotic functional traits, such as shifts between copiotrophy and oligotrophy, is fundamental to our understanding of thermal acclimation of microbially-mediated soil organic carbon cycling. Inclusion of microbial functional shifts may provide the potential to improve our projections of responses in microbial community and CO<sub>2</sub> efflux to a changing environment in forest ecosystems.</span>

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