Researchers have some bad news for future farmers and eaters: As carbon dioxide levels rise this century, some grains and legumes will become significantly less nutritious than they are today.
The new findings are reported in the journalNature. Eight institutions, from Australia, Israel, Japan and the United States, contributed to the analysis.
The researchers looked at multiple varieties of wheat, rice, field peas, soybeans, maize and sorghum grown in fields with atmospheric carbon dioxide levels like those expected in the middle of this century. (Atmospheric CO2concentrations are currently approaching 400 parts per million, and are expected to rise to 550 ppm by 2050.)
The teams simulated high CO2levels in open-air fields using a system called Free Air Concentration Enrichment (FACE), which pumps out, monitors and adjusts ground-level atmospheric CO2to simulate future conditions. In this study, all other growing conditions (sunlight, soil, water, temperature) were the same for plants grown at high-CO2and those used as controls.
The experiments revealed that the nutritional quality of a number of the world’s most important crop plants dropped in response to elevated CO2.
The study contributed “more than tenfold more data regarding both the zinc and iron content of the edible portions of crops grown under FACE conditions” than available from previous studies, the team wrote.
“When we take all of the FACE experiments we’ve got around the world, we see that an awful lot of our key crops have lower concentrations of zinc and iron in them (at high CO2),” said University of Illinois plant biology and Institute for Genomic Biology professor Andrew Leakey, an author on the study. “And zinc and iron deficiency is a big global health problem already for at least 2 billion people.”
Zinc and iron went down significantly in wheat, rice, field peas and soybeans. Wheat and rice also saw notable declines in protein content at higher CO2.
“Across a diverse set of environments in a number of countries, we see this decrease in quality,” Leakey said.
Nutrients in sorghum and maize remained relatively stable at higher CO2levels because these crops use a type of photosynthesis, called C4, which already concentrates carbon dioxide in their leaves, Leakey said.
“C4 is sort of a fuel-injected photosynthesis that maize and sorghum and millet have,” he said. “Our previous work here at Illinois has shown that their photosynthesis rates are not stimulated by being at elevated CO2. They already have high CO2inside their leaves.”
More research is needed to determine how crops grown in developing regions of the world will respond to higher atmospheric CO2, Leakey said.
“It’s important that we start to do these experiments in tropical climates with tropical soils, because that’s just a terrible gap in our knowledge, given that that’s where food security is already the biggest issue,” he said.
The above story is based on materialsprovided by University of Illinois at Urbana-Champaign
Brown Mang Onwuka
The carbon cycle is a complex thing. There is carbon in the air (carbon dioxide), carbon in plants and animals, dissolved carbon in the sea and carbon in the soil that is constantly circulating to and from. Elevated levels of atmospheric carbon dioxide may accelerate carbon cycling and soil carbon loss in forests, as found in new research led by an Indiana University biologist. The new evidence supports an emerging view that although forests remove a substantial amount of carbon dioxide from the atmosphere, much of the carbon is being stored in living woody biomass rather than as dead organic matter in soils.
Soil carbon is the generic name for carbon held within the soil, primarily in association with its organic content. Soil carbon is the largest terrestrial pool of carbon. Soil carbon plays a key role in the carbon cycle and thus is important in global climate models.
Richard P. Phillips, lead author on the paper said that after nearly two decades of research on forest ecosystem responses to global change, some of the uncertainty has been lifted about how forests are storing carbon in the wake of rising carbon dioxide levels.
“It’s been suggested that as trees take up more carbon dioxide from the atmosphere, a greater amount of carbon will go to roots and fungi to acquire nutrients, but our results show that little of this carbon accumulates in soil because the decomposition of root and fungal detritus is also increased,” he said.
Carbon stored in soils, as opposed to in the wood of trees, is desirable from a management perspective in that soils are more stable over time, so carbon can be locked away for hundreds to thousands of years and not contribute to atmospheric carbon dioxide increases.
The research was conducted at the Duke Forest Free Air Carbon Dioxide Enrichment site in North Carolina. At this site, mature loblolly pine trees were exposed to increased levels of carbon dioxide for 14 years, making it one of the longest-running carbon dioxide enrichment experiments in the world. Researchers were able to calculate the age of the carbon cycling through the soil by growing roots and fungi into mesh bags that contained uniquely labeled soils. The soils were then analyzed for their organic composition.
The authors also report that nitrogen cycled faster in this forest as the demand for nutrients by trees and microbes became greater under elevated CO2.
“The growth of trees is limited by the availability of nitrogen at this site, so it makes sense that trees are using the extra carbon taken up under elevated CO2 to prime microbes to release nitrogen bound up in organic matter,” Phillips said. “What is surprising is that the trees seem to be getting much of their nitrogen by decomposing root and fungal detritus that is less than a year old.”
The two-fold effects of microbial priming, where microbes are stimulated to decompose old soil organic matter via an increase in new carbon and other energy sources, and the faster turnover of recently fixed root and fungal carbon, are enough to explain the rapid carbon and nitrogen cycling that is occurring at the Duke Forest site.
Tropical forests are important globally in removing carbon from the atmosphere. It has been assumed that the tress were the mechanism that made this work. New research from Princeton University has shed insight on the importance of bacteria that co-exist with the trees have in absorbing atmospheric carbon.
Continue reading New insight on how tropical forests capture carbon.
University of Montana researchers examined the impact that converting natural land to cropland has on global vegetation growth, as measured by satellite-derived net primary production, or NPP. They found that measures of terrestrial vegetation growth actually decrease with agricultural conversion, which has important implications for terrestrial carbon storage.
Continue reading Converting land to agriculture reduces carbon uptake, study shows