In situ gas-exchange: automated, light-dark measurements of CO2 fluxes on a geothermal temperature gradient in a Sub-Arctic grassland ecosystem&#160;
Authors: Avila Linsey Marie , Steenberg Larsen Klaus , Sigurdsson Bjarni D. , Sigurdsson Pall 
Published: March 2021

&lt;p&gt;Climate effects are projected to be largest in Arctic and Sub-Arctic regions of the world with these areas being affected fourfold when compared to other areas around the globe. Because these regions are so susceptible to the changing climate, research into how these ecosystems will be affected by rising temperatures is essential. A large majority of current research points to a mass greening of the northern latitudes with higher temperatures, leading to an enhanced uptake of CO&lt;sub&gt;2&lt;/sub&gt;. While this is already documented, these ecosystems also possess a significant soil organic carbon pool with a high CO&lt;sub&gt;2&lt;/sub&gt; emission potential. The net climate feedback of Arctic ecosystems therefore remain highly uncertain. Utilizing high-frequency measurements of ecosystem-level carbon exchange in these regions could unearth a valuable understanding of just how rising temperatures will affect the soil-plant continuum in varying future climate scenarios.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;For the newly established FutureArctic project, located at ForHot in Iceland, we installed four ECO&lt;sub&gt;2&lt;/sub&gt;flux automated chambers at one of the naturally heated grasslands sites in July of 2020. The automatic chambers were placed at different locations along a soil temperature gradient with treatments covering an average of 0, 3.5, 7.5, and 12.5 degree warming above the ambient temperature. The major aim is to investigate the underlying carbon balance processes in order to ascertain a better insight into how future climate change induced temperature increases could affect such ecosystems. We hypothesize that the detailed analysis of carbon uptake (gross primary production, GPP) and carbon release (ecosystem respiration, R&lt;sub&gt;E&lt;/sub&gt;) along the temperature gradient will expose a latent change from net carbon sink to net carbon source as temperatures increase.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Preliminary analysis for the first nine months was conducted. The fluxes of CO&lt;sub&gt;2&lt;/sub&gt; showed evident heterogeneity between the conditions with a greater overall increase of R&lt;sub&gt;E&lt;/sub&gt; than GPP with increasing temperature. During the growing season GPP was highest in the third treatment with warming between +5 to 10 degrees, which supports the Arctic greening hypothesis. At the highest temperature treatment, GPP was much lower than in the ambient treatment indicating a drop off in ecosystem productivity and, quite possibly, a temperature threshold for this ecosystem. The observed temperature response appears non-linear with a threshold of about +10&amp;#176;C where both GPP and R&lt;sub&gt;E&lt;/sub&gt; decrease. Knowledge of these non-linear temperature responses for GPP and R&lt;sub&gt;E&lt;/sub&gt; will be of great importance when trying to predict future changes to the carbon balance in Arctic and Sub-Arctic ecosystems.&lt;/p&gt;