Shihab Uddin1 2, Markus Löw1, Shahnaj Parvin2 3, Glenn Fitzgerald1 4, Sabine Tausz-Posch1, Roger Armstrong4, Garry O’Leary4, Michael Tausz3
1Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, 4 Water Street, Creswick, VIC-3363, Australia. Email:firstname.lastname@example.org.
2Department of Agronomy, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.
3School of Ecosystem and Forest Sciences, The University of Melbourne, 4 Water Street, Creswick, VIC-3363 Australia.
4Department of Economic Development, Jobs, Transport and Resources, Private Bag 260, Horsham, VIC-3401, Australia.
Increasing atmospheric CO2 concentration ([CO2]) has profound effects on plant growth, yield and water use. Elevated atmospheric [CO2] (e[CO2]) increases above- and below ground biomass production of wheat. The increased root growth under e[CO2] may allow the extraction of subsoil water, which is especially important in hot and dry Mediterranean conditions when the top soil dries off quickly. A glasshouse experiment was conducted with hydraulically separated top and bottom layered soil column to investigate the effect of soil drying at different depths on growth and gas exchange of wheat under e[CO2]. Drought stress was induced either in the top or the bottom soil layer or both by withholding 33% of the irrigation. Drought treatments started at stem elongation. At the flowering growth stage, net photosynthetic assimilation rate (Anet) stomatal conductance (gs), as well as above- and below ground biomass were measured.
In our study, Anet was higher and gs was lower under e[CO2] than a[CO2], which resulted in greater intrinsic water use efficiency (iWUE). Above- and below ground biomass production of wheat under e[CO2] were higher compared to a[CO2]. Under e[CO2], wheat produced more biomass than under a[CO2] well-watered conditions even if either the top or bottom layer were subjected to drought treatment. In the DW treatment (D = drought, W = well-watered, where the first letter denotes the top layer and second letter denotes the bottom layer) vigorous root growth under e[CO2] increased the accessibility to the moisture in the bottom layer and resulted in gs similar to that of the WD. In addition, the reduction of above ground biomass in DW treatment was lower compared to DD conditions under e[CO2]. Therefore higher below ground production of wheat under e[CO2] could be able to ameliorate the potential effect of drought by improving accessibility of sub-soil water.