Abstract
Pre-anthesis drought is expected to greatly increase yield losses in wheat (Triticum aestivum L.), one of the most important crops worldwide. Most studies investigate the effects of pre-anthesis drought only at maturity. The physiology of the plant before anthesis and how it is affected during drought is less studied. Our study focused on physiological patterns in wheat plants during pre- and post-anthesis drought. To this end, we measured leaf xylem water potential, osmotic potential and water content in different plant parts at a high temporal frequency: every 3 days, three times a day. The experiment started just before booting until 2 weeks after flowering. Drought stress was induced by withholding irrigation with rewatering upon turgor loss, which occurred once before and once after anthesis. The goal was to investigate the patterns of osmotic adjustment, when it is used for protection against drought, and if the strategy changes during the phenological development of the plant. Our data gave no indication of daily osmotic adjustment, but did show a delicate control of the osmotic potential during drought in both leaves and stem. Under high drought stress, osmotic potential decreased to avoid further water loss. Before anthesis, rewatering restored leaf water potential and osmotic potential quickly. After anthesis, rewatering restored water potential in the flag leaves, but the osmotic potential in the stem and flag leaf remained low longer. Osmotic adjustment was thus maintained longer after anthesis, showing that the plants invest more energy in the osmotic adjustment after anthesis than before anthesis. We hypothesize that this is because the plants consider the developing ear after anthesis a more important carbohydrate sink than the stem, which is a carbohydrate sink before anthesis, to be used later as a reserve. Low osmotic potential in the stem allowed turgor maintenance, while the low osmotic potential in the flag leaf led to an increase in leaf turgor beyond the level of the control plants. This allowed leaf functioning under drought and assured that water was redirected to the flag leaf and not used to refill the stem storage.
Highlights
Wheat is contributing for 20% of the caloric and protein intake of the human population (Lobell and Gourdji, 2012; Shiferaw et al, 2013; Cosgrove, 2021)
The present study focused on assessing the physiology, and more particular the osmotic adjustment, of a drought sensitive wheat cultivar experiencing both pre- and post-anthesis drought
The lowest soil water potential values still corresponded to 2–4% Volumetric Water Content (VWC) and do not indicate drought stress yet
Summary
Wheat is contributing for 20% of the caloric and protein intake of the human population (Lobell and Gourdji, 2012; Shiferaw et al, 2013; Cosgrove, 2021). Climate change is endangering the global food productivity, and local food security (Lobell and Gourdji, 2012). Drought affects 60% of the wheat production in high-income countries and 30% in least developed countries (Chen et al, 2012; Ahmad et al, 2018). To keep up with the demand, strategies need to be developed to increase wheat yield under this changing environment (Ray et al, 2013; Hunter et al, 2017). This will require the collaboration of plant physiologists, plant breeders, geneticists, agronomists, computer scientists and more. Crop management decisions can be improved or new targets for breeding can be discovered
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