High-resolution spatial patterns and drivers of terrestrial ecosystem carbon dioxide, methane, and nitrous oxide fluxes in the tundra

<p>Arctic terrestrial greenhouse gas (GHG) fluxes of carbon dioxide (CO<span class="inline-formula">₂</span>), methane (CH<span class="inline-formula">₄</span>), and nitrous oxide (N<span class="inline-formula">₂</span>O) play an important role in the global GHG budget. However, these GHG fluxes are rarely studied simultaneously, and our understanding of the conditions controlling them across spatial gradients is limited. Here, we explore the magnitudes and drivers of GHG fluxes across fine-scale terrestrial gradients during the peak growing season (July) in sub-Arctic Finland. We measured chamber-derived GHG fluxes and soil temperature, soil moisture, soil organic carbon and nitrogen stocks, soil pH, soil carbon-to-nitrogen (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">C</mi><mo>/</mo><mi mathvariant="normal">N</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="a1fd226718b6fd2378e4d645ff1b8807"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-335-2024-ie00001.svg" width="24pt" height="14pt" src="bg-21-335-2024-ie00001.png"/></svg:svg></span></span>) ratio, soil dissolved organic carbon content, vascular plant biomass, and vegetation type from 101 plots scattered across a heterogeneous tundra landscape (5 km<span class="inline-formula">²</span>). We used these field data together with high-resolution remote sensing data to develop machine learning models for predicting (i.e., upscaling) daytime GHG fluxes across the landscape at 2 m resolution. Our results show that this region was on average a daytime net GHG sink during the growing season. Although our results suggest that this sink was driven by CO<span class="inline-formula">₂</span> uptake, it also revealed small but widespread CH<span class="inline-formula">₄</span> uptake in upland vegetation types, almost surpassing the high wetland CH<span class="inline-formula">₄</span> emissions at the landscape scale. Average N<span class="inline-formula">₂</span>O fluxes were negligible. CO<span class="inline-formula">₂</span> fluxes were controlled primarily by annual average soil temperature and biomass (both increase net sink) and vegetation type, CH<span class="inline-formula">₄</span> fluxes by soil moisture (increases net emissions) and vegetation type, and N<span class="inline-formula">₂</span>O fluxes by soil <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">C</mi><mo>/</mo><mi mathvariant="normal">N</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="5eeb1c5cb631cedd0f3a8dec9feeaf61"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-335-2024-ie00002.svg" width="24pt" height="14pt" src="bg-21-335-2024-ie00002.png"/></svg:svg></span></span> (lower <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">C</mi><mo>/</mo><mi mathvariant="normal">N</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="9a0fb47100c852e2eda5b51d5d8036ea"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-335-2024-ie00003.svg" width="24pt" height="14pt" src="bg-21-335-2024-ie00003.png"/></svg:svg></span></span> increases net source). These results demonstrate the potential of high spatial resolution modeling of GHG fluxes in the Arctic. They also reveal the dominant role of CO<span class="inline-formula">₂</span> fluxes across the tundra landscape but suggest that CH<span class="inline-formula">₄</span> uptake in dry upland soils might play a significant role in the regional GHG budget.</p>