In-House Research

In-House Research using EPA's Terracosm Facility

Effect of Asymmetric vs Symmetric Warming on Grassland Mesocosms

Our research goal is to determine whether elevated temperature impacts carbon, water, and nutrient cycles similarly under different daily temperature profiles.

IPCC Report, 2007


Although extensive research has determined ecosystem responses to equal increases in day and night temperatures, current temperature increases in many regions have been asymmetrical, with increases in minimum temperature (Tmin) exceeding increases in maximum temperature (Tmax), or vice versa, depending on location.

On average across the globe, Tmin has increased faster than Tmax, leading to a -0.066°C per decade decrease in diel temperature range between 1950-2004 (Vose et al. 2005).

Experimental Design

We are comparing three treatments with alternative temperature regimes:

  1. Ambient tracks current temperature
  2. Symmetric is +3.5C warmer all the time.
  3. Asymmetric is +5C warmer at dawn (Tmin), and +2.5C warmer at midday (Tmax).

symmetric treatment has higher daily maximum temperatures than the asymmetric treatment, but is cooler at night and in the early morning.


+/- symbols indicate  expected impacts of elevated temperature on plant growth

We hypothesize several potential outcomes for plant growth

Hypothesize 1.) Plants should grow more under symmetric than asymmetric warming, because greater warming during the daytime will enhance photosynthesis more than respiration.

Hypothesize 2.) Plants should grow more under asymmetric than symmetric warming, because high midday temperatures are stressful and reduce photosynthesis.

Same outcome as Hypothesize 2, but for a different reason...

Hypothesize 3.) Plants should grow more under asymmetric than symmetric warming, because less severe cold at night would reduce winter dormancy and extend the growing season.

Hypothesize 4.) No difference between asymmetric and symmetric treatments, due to a combination of effects.