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 the newest long-term experiment in the Global Change Research Wetland. SMARTX is a whole-ecosystem active warming experiment that also includes elevated CO2, allowing scientists to study wetland responses to two interlinked global change factors.

Visit the Global Change Research Wetland homepage

The Question

This fourth GCReW experiment is dedicated to understanding the ecosystem-scale consequences of warming and elevated CO2 in tidal wetlands at the coastal terrestrial-aquatic interface. In particular, we are looking how the plant- and microbial-driven processes that regulate coastal wetland carbon sequestration are affected by the combination of warming and elevated CO2 and what that means for coastal wetlands and other ecosystems in the future.

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.

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!