Is there a yield cost for limiting water loss during the hot hours of the day in wheat?

The demand for staple foods such as wheat continues to increase as the world’s population grows. In Australia, the 6^th highest grain producing country in the world, drought frequently limits wheat production and climate change is projected to further impact crops through increased temperature, increased CO₂, and increased rainfall variability.

Great attention has been given to growing plants with reduced transpiration – water loss through stomata – by reducing stomatal conductance during the hot hours of the day, when evaporative demand is the greatest. Yet, there is a tradeoff between reducing stomatal conductance to limit water efflux and its influence on CO₂ flux into the leaves, which may reduce photosynthesis and biomass accumulation.

A new study published in in silico Plants found that limiting transpiration rate in dry conditions can improve wheat productivity. In the study, a team of researchers at the Queensland Alliance for Agriculture and Food Innovation (QAAFI) at the University of Queensland modeled how genotypic variability in transpiration impacts yield using a newly developed transpiration module for the APSIM NextGen framework with improved for canopy development.

Contrasting genotypes were grown on lysimeter platforms to determine their transpiration rates in response to evaporative demand. Data from the lysimeter experiment was used to simulate wheat growth across the Australian wheatbelt under current and future climate scenarios. In the simulation, one reference genotype and two virtual genotypes with transpiration rate reduced by 30% or 100% at high evaporative demand were compared to determine the relative gain or penalty on traits such as grain yield.

The researchers not only found that under drought conditions reduced transpiration at high evaporative demand could led to a relatively similar biomass production. Under the current climate, this ability of some genotypes to reduce their transpiration during the hot hours of the day could increase wheat yield by 1-5%, depending on the region considered. In the dryer and warmer future, it could increase grain yield by 2-12% on average.

According to lead author Dr. Brian Collins, “limiting transpiration at high evaporative demands appears to be a promising trait for selection by breeders, especially in drought-prone environments where water can be conserved in the soil.”