The response of soil-profile temperatures to climate change and potential impacts on decomposition, plant processes, and nutrient cycling.

Despite the importance of soil temperature for ecosystem functioning, agricultural production, and carbon-climate feedbacks, the impact of projected climate change on soil temperature has received little attention in comparison to land-surface temperatures. We evaluated soil warming predictions for 14 models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), and how warming varies by soil order, soil depth, latitude, and magnitude of air warming. The model ensemble prediction was annual average warming of 2.5 ± 0.7 and 4.5 ± 1.1 ºC (mean ± sd) by 2100 for RCP 4.5 and 8.5, respectively. Soil warming in deep soil (evaluated to 1 m) nearly keeps pace with air warming except in regions with significant snow or soil ice. This talk will consider model results as well as warming experiments in temperate forest and Arctic tundra. Given our recent experimental results that decomposition of deep soil carbon is vulnerable to warming, this suggests that in many regions the whole profile of soil carbon is available to contribute climate feedbacks. Moreover, soil temperatures affect root functioning and nutrient cycling, including plant nitrogen uptake outside the growing season. Thus, deeper understanding is needed about plant, microbial, and biogeochemical response to warming in subsoils.