WIKIMEDIA, RICHARD WEBB Not all plants fix carbon from the atmosphere in the same way. More than 90 percent of the plants use a carbon fixation known as C 3 ; others, such as corn and sugarcane, use a variation of the process known as C 4 carbon fixation. Due to their biology, C 4 plants were considered to be less reactive than C 3 plants for changes in carbon dioxide concentration for a long time – an important difference that should be considered when studying plants (1
C 3 and C 4 respond differently to changes in carbon dioxide concentration molecular pathways they use to extract the gas from the atmosphere. While C 3 plants use an enzyme known as RuBisCO to fix carbon in a 3-carbon compound, C uses 4 plants – many of them grasses and important crops – another enzyme first generates a compound with 4 carbon atoms.
The enzyme of C 4 plants has a much higher affinity for carbon dioxide molecules, leading the researchers to hypothesize that these plants gain less with increasing carbon dioxide concentrations than their C 3 cousins
Many experiments have supported this hypothesis – and the data from the first 12 years of this last experiment, conducted in Minnesota, were no different. During this time, C 3 plants grown in elevated carbon dioxide levels had an average biomass increase of 20 percent compared to control plants grown under ambient conditions, while C showed 4 plants a 1 percent gain compared to their locally grown counterparts.
But then the tables turned. In the next eight years of the experiment, C 4 plants gained 24 percent more biomass than their locally grown counterparts, while C 3 plants averaged about 2 percent less.
The researchers do not know what is behind the trend change, although in their publication they point out that the amount of available nitrogen in the soil varies in accordance with the growth rates of the two plants. (19659003) Nevertheless, the findings are "a big surprise," as co-author Peter Reich, an ecologist at the University of Minnesota at Saint Paul, Nature explains] "I do not think a scientist in the world it would have predicted. "
The study has relevance for climate models that include estimates of the ability of plants to absorb carbon dioxide from the atmosphere. The new findings indicate that C 3 plants could contribute less to the absorption of carbon dioxide than previously thought, but C 4 could contribute more grassland. "The key message is that you do not count grassland C 4 ," says Dana Blumenthal, an ecologist at the US Department of Agriculture in Fort Collins, Colorado Nature  The Unexpected Reversal of Plant Growth highlights, however, the need for longer-term experiments, says Richard Norby, a forest ecologist at the Oak Ridge National Laboratory in Tennessee, who was not involved in this project Nature . "You can not do it with short experiments."