Research ProjectSalt Marsh Accretion Response to Temperature eXperiment (SMARTX)

Infrared lamps over wetland

Warming and elevated CO2 experiment in the Global Change Research Wetland. Heat lamps warm the plants from above, while cables heat the soil.


The Salt Marsh Accretion Response to Temperature eXperiment (SMARTX) is a whole-ecosystem active warming experiment in the Global Change Research Wetland dedicated to understanding the ecosystem-scale consequences of warming and elevated CO2 on carbon cycling in tidal wetlands. In particular, we are looking at how the plant- and microbial-driven processes that regulate coastal wetland carbon sequestration are affected by multiple simultaneous ecosystem stressors (warming and elevated CO2) and what that means for coastal wetlands and other ecosystems in the future. The interdisciplinary team includes researchers from SERC, Virginia Institute of Marine Science, Oak Ridge National Lab, USGS, and Rider University. SMARTX has been supported by the US Department of Energy Environmental System Science program since 2016.

Visit the Global Change Research Wetland homepage

How It Works

In 2016, Smithsonian scientists set up 30 new plots that are exposed to a range of warming. Some plots are left at ambient temperatures, while others are heated year-round to 1.7°C, 3.4°C, and 5.1°C above ambient using a combination of infrared lamps and belowground heating cables. An integrated feedback control system allows the heating system to be constantly adjusted to keep each plot at exactly the right temperature. The experiment is set up in two areas of the wetland, to compare how different plant communities respond to warming, and each treatment is repeated three times, to capture any spatial variability. There are also some plots with open-top chambers that are used to increase the atmospheric CO2 concentration to 750 parts per million, like in the CO2 and nitrogen experiment. SMARTX was the first replicated experiment in any terrestrial ecosystem that combined feedback-controlled whole-ecosystem warming with elevated CO2.

Three images of warming plots: with cables visible, with green plants, and with melted snow.
Each transect is set up along a heating gradient running from ambient (foreground) to +5.1°C above ambient (background). Soils are heated down to 1.5 m using vertical "pins" made from resistance cable. The aboveground temperature is elevated using infrared heaters. Left: Yellow soil heating cables. Middle: Earlier spring plant emergence in warmed plots. Right: Faster snow melt in warmed plots.

Discoveries and The Future

Our initial results indicate that both warming and elevated CO2 have strong effects on plant biomass allocation and methane emissions and that these results vary depending on how much the plots were warmed. Stay tuned for more details!