Climate change: more plant growth but less nutrients

First field trial tests effects of increased CO2 content on crops

Agricultural researcher Weigel on the Brunswick test fields © M. Welling
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What yields do crops bring if the carbon dioxide content of the atmosphere continues to rise as a result of climate change? This question is followed by a study by German researchers published in "Nature". Initial field trials under elevated CO2 levels suggest that while growth may be encouraged, nutrient content may decrease.

Worldwide, there is little understanding of the behavior of plants that grow on the open field in an altered atmosphere. No wonder: Such experiments in the open air are extremely time-consuming. Within the framework of a FACE (Free Air Carbon Dioxide Enrichment) project, a team led by Professor Hans-Joachim Weigel from the FAL Institute of Agroecology in Braunschweig has spent six years investigating how the yields and quality of winter wheat, sugar beets and winter barley in If the air above the field does not have the usual 380 ppm of carbon dioxide, but 550 ppm - a value that is expected in about 50 years.

In general, one assumes a "CO2 fertilization effect", as the plants use CO2 for their photosynthesis and can grow better with an increased supply of this gas. But - and this is where the Nature article begins - what is the actual rate of growth and what is the quality of the crop?

Stronger growth but fewer proteins

Although scientists like American soil researcher Bruce Kimball from Arizona, based on their enriched atmosphere experiments, believe that elevated levels of CO2 generally have a positive impact on yield levels, there can be some unexpected nutritional benefits. Because the protein content of many plant species was significantly reduced in the experiments. Perhaps an increased nitrogen fertilization could help here, because nitrogen is an important component in protein synthesis.

Within the FACE "gassing rings", the CO2 concentration of the atmosphere is set to 550 ppm FAL

Hans-Joachim Weigel dampens these expectations: "Some crops require more fertilizer than can be represented in terms of cost-effectiveness and environmental protection, " he adds in the Nature magazine -Items. Reason for this assessment are, among others, analyzes from Garching in Munich. display

There, Dr. Herbert Wieser from the German Research Center for Food Chemistry (DFA) processed the wheat from Weigel's FACE experiments into bread flour and measured the protein content. Especially the gluten proteins, which are crucial for the baking quality, were reduced by about 20 percent.

Reduction of other important ingredients

Bruce Kimball found similar protein reductions in cotton leaves. Quite likely that other plants such as pasture grass at higher CO2 content less protein. Kimball raises the question of how the herbivorous livestock reacts to this reduced protein supply in the feed.

And there are signs - among other things, based on studies by the research group of Professor Andreas Fangmeier at the University of Hohenheim - that in addition to proteins, other important for the nutrition ingredients such as vitamin C and mineral trace elements in the plants ckgehen. "Even if there is no reason for panic, we should take these results seriously, " agree Kimball and Weigel in the Nature article. And Weigel points out: "We still do not have enough basic data to be able to seriously assess all these things."

But why is it so important to know, as far as possible, how plants react to the changed CO2 supply in 50 years? Researchers know that breeding new varieties needs a long lead time. So if you want to have crops available in the future that are optimally adapted to the outside conditions, growers should know as soon as possible which ones Parameters they need to include in their breeding programs.

(Federal Research Center for Agriculture (FAL), 05.09.2007 - NPO)