U.S. Department of Energy, Office of Science

Program for Ecosystem Research

Research Project   Effect of asymmetric versus symmetric warming on grassland mesocosms

Principal investigator:   Jillian W. Gregg

Project goal

Determine the effect of asymmetrical versus symmetrical increases in the diel temperature cycle on constructed grassland mesocosms.

Oregon ecosystems

Regions of Oregon.

Ecosystem being studied

A grassland native to Oregon's Willamette Valley. A grassland ecosystem was chosen because of the complex mixture of species types (e.g., grass/forb, annual/perennial, N-fixers/not) and because they are expected to achieve 100% of mature ecosystem biomass within the course of the experiment.


The grassland systems have been constructed in the Terracosm facility (see below) and temperature treatments have been imposed for a full growing season.

Why this is important

Results of this research will determine whether patterns of increased growth shown for symmetric warming experiments are similar, though muted, for asymmetric profiles, or whether entirely different patterns emerge that are unique to the asymmetrically elevated temperature treatments meant to reflect likely diel patterns of future warming.

The mescosms

The mesocosms being used.


The research is being performed in the U.S. EPA's Terracosm Research Facility (Corvallis, OR). The facility involves outdoor, sunlit, closed chambers that can be used as a combined cuvette/lysimeter system to monitor both aboveground and belowground carbon, water, and nutrient fluxes.

The experimental treatments (n = 4 chambers for each treatment) are: (a) ambient air temperature patterns, (b) symmetric (i.e., continuous) warming of 3.5 degrees Celsius, and (c) asymmetric (i.e., variable) warming of 2 degrees during the day and 5 degrees during the night.

Soils were collected from a native Willamette Valley grassland site that had not been disturbed over the past 100 years. Soils were excavated by horizon to a depth of 1 m during the dormant dry period in mid September before the onset of fall rains. Roots and rocks were sieved from the soils before placing them into the soil box lysimeters by horizon and tamping them to the same bulk density. An initial layer of gravel was placed on the 5.7 degree sloped bottom to provide ample drainage. To minimize the need to weed introduced plants the top 5 cm of soil was steam pasteurized. Soil temperature and moisture probes and soil gas wells were placed at 5, 15, 35, 55, and 75 cm depths, with minirhizotron tubes placed at 15, 35, and 55 cm. Sensor depths were chosen to access the most active rooting zones and provide a profile across the soil horizons.


Jillian W. Gregg, Terrestrial Ecosystems Research Associates

David M. Olszyk, Environmental Protection Agency, Western Ecology Division (subaward)

Funding period:   May 2005 to present