High temporal resolution measurements of subarctic carbon exchange following natural soil temperature manipulation

According to contemporary research, mass greening of the northern latitudes is likely to take place as global temperatures continue to rise. While this could support an overall increase in autotrophic uptake of CO₂, rising temperatures could also expose a higher CO₂ emission potential as reparation rates respond to our changing climate. Thus, the future carbon balance in high-latitude ecosystems remains 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 under varying future climate scenarios.

Over the course of a two year study period, we measured in-situ carbon exchanges using four ECO₂flux automated chambers at one of the geothermal grasslands sites within the FutureArctic network. The chambers were placed at different locations along a soil temperature gradient with treatments covering an average of 0, 2.5, 8.5, and 15.0 degree warming. The major aim was to investigate the underlying carbon exchange processes in order to garner better insight into how future climate change induced temperature increases could affect comparable ecosystems under long-term warming. Following a detailed analysis of carbon uptake (gross primary production, GPP) and carbon release (ecosystem respiration, R_E) along the temperature gradient would likely expose a positive net plant carbon uptake with increasing temperature as a direct response to the greening effect while respiration could remain lower than GPP, follow a similar trajectory, or offset this increase in uptake entirely depending on length of exposure to soil warming.

Preliminary analysis from a subset within the two-year study period was conducted. The fluxes of CO₂ showed evident heterogeneity between our four treatments with increasing totals of GPP moving up the temperature gradient. However, during this period, GPP was highest in the treatment with warming around 8.5 degrees above ambient, which suggests that there is likely a temperature threshold for increased uptake with greening between 8.5 to 15 degrees soil warming for this ecosystem. The observed temperature response appears non-linear where both GPP and R_E start to decline after reaching this temperature threshold. Knowledge of these non-linear temperature responses for GPP and R_E will be of great importance when trying to predict future changes to the carbon balance in Arctic and Sub-Arctic ecosystems.