Description:
<jats:title>Summary</jats:title><jats:p>Identification of microbes that actively utilize root exudates is essential to understand plant–microbe interactions. To identify active root exudate‐utilizing microorganisms associated with switchgrass – a potential bioenergy crop – plants were labelled <jats:italic>in situ</jats:italic> with <jats:sup>13</jats:sup><jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>, and 16<jats:styled-content style="fixed-case">S</jats:styled-content> and 18<jats:styled-content style="fixed-case">S rRNA</jats:styled-content> genes in the <jats:sup>13</jats:sup><jats:styled-content style="fixed-case">C</jats:styled-content>‐labelled rhizosphere <jats:styled-content style="fixed-case">DNA</jats:styled-content> were pyrosequenced. Multi‐pulse labelling for 5 days produced detectable <jats:sup>13</jats:sup>C‐<jats:styled-content style="fixed-case">DNA</jats:styled-content>, which was well separated from unlabelled <jats:styled-content style="fixed-case">DNA</jats:styled-content>. <jats:styled-content style="fixed-case"><jats:italic>M</jats:italic></jats:styled-content><jats:italic>ethylibium</jats:italic> from the order <jats:styled-content style="fixed-case">B</jats:styled-content>urkholderiales were the most heavily labelled bacteria. <jats:styled-content style="fixed-case"><jats:italic>P</jats:italic></jats:styled-content><jats:italic>ythium</jats:italic>, <jats:styled-content style="fixed-case"><jats:italic>A</jats:italic></jats:styled-content><jats:italic>uricularia</jats:italic> and <jats:styled-content style="fixed-case"><jats:italic>G</jats:italic></jats:styled-content><jats:italic>alerina</jats:italic> were the most heavily labelled eukaryotic microbes. We also identified a <jats:styled-content style="fixed-case"><jats:italic>G</jats:italic></jats:styled-content><jats:italic>lomus intraradices</jats:italic>‐like species; <jats:styled-content style="fixed-case">G</jats:styled-content>lomus members are arbuscular mycorrhizal fungi that are able to colonize the switchgrass root. All of these heavily labelled microorganisms were also among the most abundant species in the rhizosphere. Species belonging to <jats:styled-content style="fixed-case"><jats:italic>M</jats:italic></jats:styled-content><jats:italic>ethylibium</jats:italic> and <jats:styled-content style="fixed-case"><jats:italic>P</jats:italic></jats:styled-content><jats:italic>ythium</jats:italic> were the most heavily labelled and the most abundant bacteria and eukaryotes in the rhizosphere of switchgrass. Our results revealed that nearly all of the dominant rhizosphere bacterial and eukaryotic microbes were able to utilize root exudates. The enrichment of microbial species in the rhizosphere is selective and mostly due to root exudation, which functions as a nutrition source, promoting the growth of these microbes.</jats:p>