Genotypic variability of plant water use strategies during increasing atmospheric drought in 15 spring wheat (Triticum aestivum L.) genotypes

The rise of global temperatures and shifts in precipitation patterns lead to increasing vapour pressure deficit (VPD), which was shown to have a detrimental impact on yield of many crops. A reduction in the transpiration rate (TR) at high VPD has been proposed as a key drought tolerance breeding trait to avoid excessive water loss. Our hypothesis is that with climate change, it will be more convenient for plants to have traits that restricts TR under high VPD levels. With this research we aimed to identify relevant hydraulic traits impacting plant water use during atmospheric drying.

We measured water use and hydraulic traits of 15 different Minnesota spring wheat (Triticum aestivum L.) genotypes. We grew 45 plants (3 replicates for each genotype) in a climate chamber with controlled climatic conditions, while the soil was kept moist. After six weeks of growth, we monitored TR at 6 different VPD levels, between 0.5 and 2.8 kPa. Additionally, we measured maximum stomatal conductance (g_s), leaf area (LA), plant hydraulic conductance (K_plant), stomatal density (SD), and root and leaf total biomass.

Our findings show that total transpiration per LA, LA, and root/shoot-ratio differed significantly between genotypes. Conversely, transpiration sensitivity to rising VPD (indicated by the critical VPD upon which plants restricted transpiration, VPD_BP), K_plant and maximum g_s did not significantly differ between genotypes. However, we observed that plants with a low K_plant and a high maximum g_s expressed a relatively low VPD_BP, indicating a higher transpiration sensitivity to VPD. Our results align well with a hydraulic explanation of the TR response to increasing VPD and suggest that plant hydraulics play a key role in regulating TR during atmospheric drying. If the goal of future breeding is to modify plant water use under increasing VPD, targeting hydraulic traits has still much underexplored potential.