Climate: C02 increase bad for plants

High greenhouse gas concentration reduces protein content of cereals and grass

CO2 fumigation plant in the field © FAL
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If the concentration of the greenhouse gas CO2 in the atmosphere rises to record levels in the future, the quality of many crops will decline. As researchers of the Federal Agricultural Research Center (FAL) have determined, under these conditions, the nitrogen content of cereals and grass significantly reduced. This not only affects food and feed quality, it also affects ecosystems.

The rapid increase in CO2 concentration in the atmosphere is one of the surest signs of global climate change. The increase in the concentration of this gas will continue in the future with even greater intensity than before, according to forecasts by almost all experts. In just 50 years, the CO2 concentration should already be around 450 to 550 parts per million (ppm). That would mean an increase of nearly 50 percent compared to the current value of 375 ppm.

Increasing atmospheric CO2 levels, however, not only contribute to the warming of the Earth's atmosphere, but also have a direct effect on plants, as increased CO2 concentrations can stimulate plant growth (so-called CO2 fertilization effect).

Climate change with positive and negative effects

Predictions on the possible consequences of climate change on the terrestrial ecosystems and thus also on the agriculture of a specific region are decisively influenced by the extent to which this direct CO2 effect is taken into account in its effect on the plants. The extent of the potential CO2 impact therefore requires realistic estimates. The Institute of Agroecology of the Federal Agricultural Research Center (FAL) in Braunschweig has carried out numerous experimental studies on this topic in recent years. In addition to laboratory tests and outdoor chambers, this includes field investigations into crop rotations with extensive free-field CO2 fumigation systems.

However, the generally positive growth effect of increased CO2 concentrations is offset by a rather disadvantageous effect. In some studies, scientists have found that the levels of key macro- and microelements and other ingredients are changing under future atmospheric CO2 scenarios. FAL researchers have now addressed this issue in a new study. display

Less nitrogen means less protein

Over the last few years, they have carried out CO2 enrichment experiments (550-650 ppm) with the forage plant ryegrass and various cereals. The experiments in the laboratory and in the wild prove, independent of the different experimental conditions, that a high CO2 content in most cases leads to a significant reduction of nitrogen (N) content (and therefore of crude protein content) in both ryegrass and Cereal grains led. The extent of this N-loss varied depending on the type and management condition examined. A connection to the N supply of the test plants could not be determined. White Clover, which was also studied, did not respond with N-quality losses.

From such scenarios of future CO2 concentrations, the researchers now not only want to derive possible consequences with regard to food and feed quality, but also to investigate the consequences for the agricultural ecosystem. Changes in the quality of the food source could, for example, lead to altered growth, persistence and dispersal behavior of herbivorous insects and other pests. For the metabolic rate in the ecosystem, an increased C / N ratio of the resulting plant residues may also mean that the litter decomposition or mineralization in the soil is affected.

(idw - FAL, 14.04.2005 - DLO)