Dependence of soil respiration on temperature and moisture: Results from a site-based multivariate model in Alaska

As Arctic and Boreal ecosystems change under a warming climate, rates of soil respiration are expected to increase. It is essential to have a proper understanding of the drivers of soil respiration to accurately assess and predict how soil respiration will respond to climate warming. To improving mechanistic understanding of soil respiration, we employed a multivariate model using field-based data from 10 different sites across Alaska spanning both burned and unburned tundra and boreal ecosystems, and continuous and discontinuous permafrost zones. Automated soil respiration stations were used to measure soil surface CO₂ flux from three forced diffusion chambers at an hourly interval from 2016 to 2018. Soil moisture and soil temperature were also measured at an hourly frequency at each site. Other site variables that were measured, and included in the model were soil temperature, soil moisture, bulk density, soil organic matter, above ground biomass, vegetation type and soil pH. The model runs show that soil temperature is the primary driver of soil respiration across all of the sites. Soil moisture, however, became the dominant driver beyond a certain threshold - suppressing respiration in soils with high moisture content, and limiting respiration with low moisture content. Site disturbances, such as fire, also have an important impact on soil respiration - fire disturbance can have a significant influence on soil temperature and soil moisture regimes. The results from this site-based model study provides valuable insights on the drivers of soil respiration, which can help to improve predictions of soil respiration in the context of a changing climate.