Dr Xiaojuan Feng1,2, Dr Juan Jia1, Dr Jin-Sheng He3

1Institute Of Botany, Chinese Academy Of Sciences, Beijing, China, 2University of Chinese Academy of Sciences, Beijing, China, 3Lanzhou University, Lanzhou, China

Subsoil contains >50% of soil organic carbon (SOC) stocks globally and is conventionally assumed to be unresponsive to warming compared to the topsoil. Recent theoretical and laboratory studies suggest that deep SOC may not be as inert as previously thought. However, field-based evidence is still lacking to prove subsoil’s response to warming and its underlying mechanisms. Here utilizing a long-term warming experiment on the Qinghai-Tibetan Plateau, we demonstrate that warming induced substantial changes in carbon dynamics for the subsoil but not topsoil in an alpine grassland. Driven by elevated root distribution at depth, newly synthesized carbon accumulated in the silt-clay fraction of subsoils under warming, accompanied by increased concentrations of lipids, sugars and water-soluble peptides of both microbial and plant origins. However, lignin degradation increased in the subsoil (especially in macroaggregates) with shortening of soil freezing period and labile carbon-fueled microbial co-metabolism. These changes stand in sharp contrast to the unaltered carbon characteristics in the topsoil, suggesting that the warming response of topsoil may not reflect shifting soil carbon processes at depth. More importantly, as warming is accompanied by deepening roots in a wide range of ecosystems, root-driven priming of native SOC versus new carbon accrual needs to be evaluated beyond alpine systems to determine the future patterns and magnitude of soil carbon stock changes in a warmer world. Overall, our study delivers a mechanistic understanding for the high sensitivity of subsoil carbon dynamics to warming, which has significant implications for improving soil carbon models and predictions.

Biography: Dr. Xiaojuan Feng, PI, Institute of Botany, Chinese Academy of Sciences. Ph.D. in Geography (2009) from University of Toronto (Canada), postdoc in Woods Hole Oceanographic Institution (USA ; 2002-2010) and ETH Zürich (2010-2013). Dr. Feng is specialized at using molecular-level techniques (including biomarkers and compound-specific isotope analysis) coupled with landscape-scale experiments to examine the transformation and transport of terrestrial organic matter under global changes. She has published >25 papers as the first or corresponding author in journals including PNAS, Nature Geoscience and Nature Communications.

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