Atmospheric CO2 fertilization effects on biomass yields of 10 crops in northern Germany

The quality and quantity of the influence that atmospheric CO2 has on crop growth is still a matter of debate. This study’s aim is to estimate if [CO2] will have an effect on biomass yields at all, to quantify and spatially locate the effects and to explore if an elevated photosynthesis rate or water-use-efficiency is predominantly responsible. This study uses a numerical carbon-based crop model (BioSTAR) to estimate biomass yields within the administrative boundaries of Niedersachsen in Northern Germany. Ten crops are included (winter grains: wheat, barley, rye, triticale—early, medium, late maize variety—sunflower, sorghum, spring wheat), modeled annually for the entire twenty-first century on 91,014 separate sites. Modeling was conducted twice, once with an annually adapted [CO2] concentration according to the SRES-A1B scenario and once with a fixed concentration of 390 ppm to separate the influence of [CO2] from that of the other input variables. Rising [CO2] concentrations will play a central role in keeping future yields of all crops above or around today’s level. Differences in yields between modeling with fixed or adapted [CO2] can be as high as 60% toward the century’s end. Generally, yields will increase when [CO2] rises and decline when it is kept constant. As C4-crops are equivalently affected it is presumed that an elevated efficiency in water use is the main responsible factor for all plants.