DOI: 10.5061/dryad.h78n6s3
title: Data from: Elevated [CO2] mitigates the effect of surface drought by stimulating root growth to access sub-soil water

description: Through stimulation of root growth, increasing atmospheric CO2
 concentration ([CO2]) may facilitate access of crops to sub-soil water,
 which could potentially prolong physiological activity in dryland
 environments, particularly because crops are more water use efficient
 under elevated [CO2] (e[CO2]). This study investigated the effect of
 drought in shallow soil versus sub-soil on agronomic and physiological
 responses of wheat to e[CO2] in a glasshouse experiment. Wheat (Triticum
 aestivum L. cv. Yitpi) was grown in split-columns with the top (0–30 cm)
 and bottom (31–60 cm; ‘sub-soil’) soil layer hydraulically separated by a
 wax-coated, root-penetrable layer under ambient [CO2] (a[CO2], ∼400 μmol
 mol-1) or e[CO2] (∼700 μmol mol-1) [CO2]. Drought was imposed from
 stem-elongation in either the top or bottom soil layer or both by
 withholding 33% of the irrigation, resulting in four water treatments (WW,
 WD, DW, DD; D = drought, W = well-watered, letters denote water treatment
 in top and bottom soil layer, respectively). Leaf gas exchange was
 measured weekly from stem-elongation until anthesis. Above-and belowground
 biomass, grain yield and yield components were evaluated at three
 developmental stages (stem-elongation, anthesis and maturity). Compared
 with a[CO2], net assimilation rate was higher and stomatal conductance was
 lower under e[CO2], resulting in greater intrinsic water use efficiency.
 Elevated [CO2] stimulated both above- and belowground biomass as well as
 grain yield, however, this stimulation was greater under well-watered (WW)
 than drought (DD) throughout the whole soil profile. Imposition of drought
 in either or both soil layers decreased aboveground biomass and grain
 yield under both [CO2] compared to the well-watered treatment. However,
 the greatest ‘CO2 fertilisation effect’ was observed when drought was
 imposed in the top soil layer only (DW), and this was associated with
 e[CO2]-stimulation of root growth especially in the well-watered bottom
 layer. We suggest that stimulation of belowground biomass under e[CO2]
 will allow better access to sub-soil water during grain filling period,
 when additional water is converted into additional yield with high
 efficiency in Mediterranean-type dryland agro-ecosystems. If sufficient
 water is available in the sub-soil, e[CO2] may help mitigating the effect
 of drying surface soil.
description: Stem-elongationGrowth and morphological parameters of wheat recorded at stem-elongation (DC31).Growth and morphological parameters of wheat at stem-elongation.csvAnthesisGrowth and morphological parameters of wheat recorded at anthesis (DC65).Growth and morphological parameters of wheat at anthesis.csvMaturityGrowth, yield and morphological parameters of wheat recorded at maturity (DC90).Growth, yield and morphological parameters of wheat at maturity.csvLeaf gas exchangeNet photosynthetic assimilation rate and stomatal conductance of the flag leaf of wheat were recorded weekly using an open path infrared gas analyser (IRGA, Li-6400, Li-Cor, Lincoln, NE, USA).Soil water contentSoil water content measured in the top (0-30cm) and bottom (31-60cm) soil layers of the column used for growing wheat.