Elevated CO₂ alleviates negative effects of drought in maize: Evidence of C and N allocation and transport
Yuzheng Zong, Zhouping Shangguan ^* 

National Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences, 712100 Yangling, Shaanxi, PR China.
*Corresponding Author：Tel: (+8610) 29-87019107; Fax: (+8610) 29-87012210; E-mail: shangguan@ms.iswc.ac.cn

Abstract
The interaction of elevated carbon dioxide (CO₂) and drought result in complex responses of carbon and nitrogen delivery within plant that challenge our current understanding. The patterns of carbon and nitrogen allocation, transport and storage of maize (Zea mays L.) were investigated in this study.
Within a CO₂ (380 or 750 µmolmol^-1, climate chamber) and water stress (10% PEG-6000, -0.32 M Pa) combined experiment, we measured carbon and nitrogen delivery patterns using ¹³C and ¹⁵N as tracers.
Compared to water-stressed maize under atmospheric [CO₂], the elevated [CO₂] treatment interacted with water stress allocated more newly fixed carbon to developing leaves and increased the carbon re-mobilization from aging leaves to developing leaves, and decreased the carbon counter-flow from their roots to leaves. The maize seedlings of elevated [CO₂] treatment interacted with water stress increased the allocation of their newly assimilated nitrogen to their roots and enhanced nitrogen delivery from roots to developing and developed leaves in the following days, thus to support new leaves growth.
Maize was found capable of supporting developing leaves growth at the doubled [CO₂] by changing transport and re-mobilization strategy of carbon and nitrogen, which could partially alleviate drought stress they suffered.

Keywords: drought; doubled [CO₂]; carbon; nitrogen; allocation; transport