Altered leaf and root emissions from onion ( Allium cepa L.) grown under elevated CO 2 conditions

Abstract

Elevated atmospheric CO 2 concentrations ([CO 2]) have been hypothesized to increase photosynthesis rates and volatile organic compound (VOC) emissions; however, field measurements from a select group of conifer and angiosperm trees have shown that VOC emissions are in fact not affected or reduced by elevated CO 2 levels. To broaden the understanding of how different plant species respond to elevated atmospheric [CO 2], air-flow-through, glass chambers were designed and utilized to measure photosynthesis and emissions from onion ( Allium cepa cv. ‘Purplette’) under controlled environmental conditions. Here we report on VOC release and root exudation while monitoring photosynthesis from whole plants grown under ambient (400 μmol mol −1) and elevated (1000 μmol mol −1) [CO 2]. A 22% increase in photosynthesis in the elevated CO 2 plants and a 17-fold and 38-fold increase in the VOC hydrocarbons 2-undecanone and 2-tridecanone, respectively, were observed in 30-day-old onion seedlings compared to plants grown under ambient CO 2 conditions. In contrast TOC from root exudates decreased significantly with elevated CO 2 conditions. Plants harvested at 30 days had on average over 40% greater biomass when grown at elevated CO 2 levels. The demonstration that VOC emissions increase in plants grown under elevated [CO 2] and higher photosynthesis rates points to a fundamental difference in how carbon partitioning alters in herbaceous species such as onion versus the previously studied tree species in response to elevated concentration of atmospheric CO 2.