Free-Air Carbon dioxide Enrichment (FACE) is a method used by ecologists and plant biologists that raises the concentration of in a specified area and allows the response of plant growth to be measured. Experiments using FACE are required because most studies looking at the effect of elevated concentrations have been conducted in labs and where there are many missing factors including plant competition. Measuring the effect of elevated using FACE is a more natural way of estimating how plant growth will change in the future as the concentration rises in the atmosphere. FACE also allows the effect of elevated on plants that cannot be grown in small spaces (

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

s for example) to be measured. However, FACE experiments carry significantly higher costs relative to greenhouse experiments.

Method

Horizontal or vertical pipes are placed in a circle around the experimental plot, which can be between 1m and 30m in

diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid fo ...

, and these emit enriched air around the plants. The concentration of is maintained at the desired level through placing sensors in the plot which

feedback Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled ...

to a computer which then adjusts the flow of from the pipes.

Usage

FACE circles have been used across in parts of the United States in temperate forests and also in stands of

aspen Aspen is a common name for certain tree species; some, but not all, are classified by botanists in the section ''Populus'', of the ''Populus'' genus. Species These species are called aspens: *'' Populus adenopoda'' – Chinese aspen (Chin ...

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...

. The method is also utilized for agricultural research. For example, FACE circles have been used to measure the response of

soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu ...

plants to increased levels of

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...

and carbon dioxide at research facilities at the

University of Illinois at Urbana–Champaign The University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the Unive ...

. FACE technologies have yet to be implemented in

old growth forest An old-growth forestalso termed primary forest, virgin forest, late seral forest, primeval forest, or first-growth forestis a forest that has attained great age without significant disturbance, and thereby exhibits unique ecological feature ...

s, or key biomes for

carbon sequestration Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land ...

, such as

tropical forest Tropical forests (a.k.a. jungle) are forested landscapes in tropical regions: ''i.e.'' land areas approximately bounded by the tropic of Cancer and Capricorn, but possibly affected by other factors such as prevailing winds. Some tropical fo ...

s, or boreal forests and identifying future research priorities for these regions is considered an urgent concern. Examples of this method being used globally include TasFACE, which is investigating the effects of elevated CO₂ on a native

grassland A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur natur ...

Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...

, Australia. The National Wheat FACE array is presently being established in Horsham, Victoria, Australia as a joint project of the Victorian Department of Primary Industries and the University of Melbourne. EucFACE is Australia's only forest FACE experiment, and was established by the

University of Western Sydney Western Sydney University, formerly the University of Western Sydney, is an Australian multi-campus university in the Greater Western region of Sydney, Australia. The university in its current form was founded in 1989 as a federated network ...

in Cumberland Plain Woodland dominated by Eucalyptus tereticornis near

Richmond, New South Wales Richmond is a town in New South Wales, in the local government area of the City of Hawkesbury. It is located 19 metres above sea level on the alluvial Hawkesbury River flats, at the foot of the Blue Mountains on the Cumberland Plain. It is ab ...

in 2012. A FACE experiment began at Duke University in June 1994. The Blackwood Division of the Duke Forest contains the Forest-Atmosphere Carbon Transfer and Storage facility. This consists of four free-air enrichment plots which provide higher levels of atmospheric concentration and four plots that provide ambient control. There have been 253

publication To publish is to make content available to the general public.Berne Con ...

s reporting on the findings of the experiment.

Results

In 2004, a

meta-analysis A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting m ...

of 15 years of FACE studies, found the response to elevated using FACE only slightly increases yield in crop plants (5-7% in

rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly '' Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and ''Porteresia'', both wild and domestica ...

and 8% in

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeolog ...

). These responses were lower than was expected from previous studies that measured the effect in labs or enclosures. This has important consequences as previous projections of food production have assumed that decreases in yield as a result of

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

would be offset by increases in yield due to elevated . As of 2010, a more complete picture is emerging, with significant difference in response being observed for different plant species, water availabilities and the concentration of ozone. For example, the 2007-2010 Horsham FACE project (using wheat crops) in Victoria, Australia, found "The effect of eCO2 was to increase crop biomass at maturity by 20% and anthesis root biomass increased by 49%". This study also concludes that "a wide gene pool needs to be investigated to see if particular cultivars are able to respond more to eCO2". Increased atmospheric carbon dioxide has been found to reduce plant water use, and consequently, the uptake of nitrogen, so particularly benefiting crop yields in arid regions. The carbohydrate content of crops is increased from photosynthesis, but protein content is reduced due to lower nitrogen uptake. Legumes and their symbiotic "nitrogen fixing" bacteria appear to benefit more from increased carbon dioxide levels than most other species.

References

{{Reflist Ecological experiments