Peatland response to climate change: the role of plant roots

What is the role of plant roots in peatland carbon cycle response to climate change? We propose to investigate belowground plant responses and their implications for peatland greenhouse gas emissions and soil carbon storage. Peatlands store one-third of the global soil carbon pool and this carbon is vulnerable to climate and land-use change. These unique ecosystems have standing water tables close to the soil surface and the resulting anoxic conditions lead to slow organic matter decomposition rates. Combined with cold and acidic conditions, peatlands have accumulated vast amounts of soil carbon for the last ten thousand years. With climate change, peatland carbon sink capacity is weakening and the role of aboveground plants in peatland climate change responses has been documented for decades. However, the belowground plant responses are more difficult to study and remain unclear. Especially unclear are the mechanisms behind plant root responses to climate change and their implications for peatland carbon cycling. Plants can respond to warming and elevated CO2 (e[CO2]) by increasing photosynthesis, and lengthening their growing season. Belowground, root growth could increase or decrease, and plant resource acquisition strategies (inferred using root properties, hereafter ‘traits’) can change. Altered root traits could either increase or decrease peatland soil carbon storage, by either increasing root-derived carbon inputs or stimulating carbon losses through a ‘priming’ effect on soil microbial activity. Furthermore, increased plant productivity and evapotranspiration could eventually lead to water limitation and ultimately decrease plant productivity. All of these feedbacks remain largely unconstrained in peatlands.Thus, a key knowledge gap to predict the fate of one-third of the world’s soil carbon stored in peatlands is an understanding of how plant roots mediate carbon cycling responses to warming and e[CO2] and the role of moisture feedbacks. We will address two gaps crucial for explaining future peatland C losses (and thus the future peatland C sink capacity) across two work packages: A) Quantify the interactive effects of climate warming and e[CO2] on peatland root growth and traits at an existing large-scale whole-ecosystem climate change experiment (SPRUCE experiment in USA). B) Investigate how varying root traits influence peatland carbon cycle (specifically, soil carbon storage, and CO2 and CH4 emissions) using laboratory experiments.Our proposal will address a long-standing gap in peatland biogeochemistry, namely, the role of plant roots in regulating peatland carbon storage. Broader impacts include providing response functions for the peatland modules of Earth system models to strengthen the trait-based and belowground processes (e.g., priming) modeling of peatlands. Through this unique combination of large and fine-scale manipulative experiments combined with state-of-the-art soil science and plant trait ecology and isotopic techniques, we will improve our understanding of the fate of peatland carbon in a rapidly warming world.