Water use dynamics of dryland canola (Brassica napus L.) grown on contrasting soils under elevated CO2

Abstract

Increasing atmospheric carbon dioxide concentration ([CO2]) stimulates the leaf-level (intrinsic) water use efficiency (iWUE), which may mitigate the adverse effects of drought by lowering water use in plants. This study investigated the interactive effect of [CO2] and soil type on growth, yield and water use of canola (Brassica napus L.) in a dryland environment. Two canola cultivars (vigorous hybrid cv. ‘Hyola 50’ and non-hybrid cv. ‘Thumper’) were grown in large intact soil cores containing either a sandy Calcarosol or clay Vertosol under current ambient (a[CO2]) and future elevated [CO2] (e[CO2]), ∼550 μmol mol−1). Net assimilation rates (Anet), stomatal conductance (gs) and leaf area were measured throughout the growing season. Seed yield and yield components were recorded at final harvest. Water use was monitored by lysimeter balances. Elevated [CO2]-stimulation of iWUE was greater than the effect on leaf area, therefore, water use was lower under e[CO2] than a[CO2], but this was further modified by soil type and cultivar. The dynamics of water use throughout the growing season were different between the studied cultivars and in line with their leaf development. The effect of e[CO2] on seed yield was dependent on cultivar; the non-hybrid cultivar benefitted more from increased [CO2]. Although textural differences between soil types influenced the water use under e[CO2], this did not affect the ‘CO2 fertilisation effect’ on the studied canola cultivars. Elevated [CO2]-induced water savings observed in the present study is a potential mechanism of ameliorating drought effects in high CO2 environment. Better understanding of genotypic variability in response to water use dynamics with traits affecting assimilate supply and use can help breeders to improve crop germplasm for future climates.