Invariance of subalpine ecosystem respiration with temperature

High elevation ecosystems are predicted to experience significant regional warming, some of which is already occurring. This study investigates the effects of warming on subalpine ecosystems through a comparison of natural temperature gradients and experimental temperature manipulations at the Rocky Mountain Biological Lab in central Colorado. An elevational gradient running from 7500’ to 12,000’ serves as a natural temperature gradient of approximately 6 ^oC. A long-term experimental warming plot has been heating the soil by an effective 2 ^oC year-round since 1991 using overhead infrared heat lamps. At each of the six sites, ecosystem level respiration was measured on five plots at night using an open path IRGA inside of a 1m³ tent. Soil respiration was measured concurrently on each plot, to separate above and below ground contributions to ecosystem respiration. Measurements were taken in 2005 and 2006, and throughout each growing season to control for phenology. Surprisingly, across all sites and years, ecosystem level respiration does not depend on ambient temperatures. This invariance appears to be largely driven by increased water limitation with increased temperature. We present a simple model to account for the observed patterns that incorporates the role of temperature on ecosystem flux via interactions with soil moisture, soil carbon, and phytomass. We discuss our findings in the light of developing a more quantitative model to understand how subalpine ecosystems may respond to climate warming.