Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Increasing <jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub> concentration ([<jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>]) is thought to induce climate change and thereby increase air temperatures and the risk of drought stress, the latter impairing crop growth. The objective of this study was to investigate the effects of elevated [<jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>] and drought stress on root growth of one maize genotype (<jats:italic>Zea mays</jats:italic> cv. Simao) and two sorghum genotypes (<jats:italic>Sorghum bicolor</jats:italic> cv. <jats:italic>Bulldozer</jats:italic> and <jats:italic>Sorghum bicolor</jats:italic> × <jats:italic>Sorghum sudanense</jats:italic> cv. <jats:italic>Inka</jats:italic>) under the cool moderate climate of Central Europe. It was hypothesized that root growth stimulation due to elevated [<jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>] compensates for a reduced root growth under drought stress. Therefore, we established an experiment within a <jats:styled-content>f</jats:styled-content>ree‐<jats:styled-content>a</jats:styled-content>ir <jats:styled-content>c</jats:styled-content>arbon dioxide <jats:styled-content>e</jats:styled-content>nrichment system (<jats:styled-content style="fixed-case">FACE</jats:styled-content>) in 2010 and 2011. Sorghum and maize genotypes were grown under ambient [<jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>] (385 ppm <jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>) and elevated [<jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>] (600 ppm <jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>) and in combination with restricted and sufficient water supply. Elevated [<jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>] decreased root length density (<jats:styled-content style="fixed-case">RLD</jats:styled-content>) in the upper soil layers for all genotypes, but increased it in deeper layers. Higher [<jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>] enhanced specific root length (<jats:styled-content style="fixed-case">SRL</jats:styled-content>) of “Simao” and “Bulldozer,” however, did not affect that of “Inka.” “Simao” achieved a higher <jats:styled-content style="fixed-case">SRL</jats:styled-content> than the sorghum genotypes, indicating an efficient investment in root dry matter. Although elevated [<jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>] affected the root growth, no interaction with the water treatment and, consequently, no compensatory effect of elevated [<jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>] could be identified.</jats:p>