Wheat could require dramatically more water during future heat waves, scientists warn

LONDON

Future heat waves could bring wheat’s water needs well beyond current estimates, a new British study said Monday.

Researchers from the University of Sheffield found that stomatal pores on wheat leaves open widely during heat waves to help keep the plant cool, meaning wheat crops could use considerably more water than expected during extreme future heat waves.

The study, led by Robert Caine and Holly Croft from the School of Biosciences, revealed that wheat crops lose many of the key water-saving benefits usually associated with growth at higher atmospheric concentrations of carbon dioxide when they are exposed to heat wave conditions.

Wheat is known for providing around 20% of daily calories to humanity worldwide and is the most widely cultivated crop by land area.

However, while yields have risen dramatically over the past century, largely due to nitrogen fertilizers, this has increased the crop’s thirst for water and made it more vulnerable to drought, according to the study.

When scientists examined wheat under high CO2 heat wave conditions, they discovered that stomata open much more widely, seemingly to increase water flow and help the plant cool through increased evapotranspiration.

It noted that during heat waves, wheat stomata also failed to respond effectively to changing light levels, irrespective of the CO2 growth concentration.

"This reduced responsiveness during heatwaves means that wheat cannot narrow its stomata effectively when light levels drop, a process that would normally help limit water loss," according to the research.

It warned that this lack of stomatal closure has the potential to reduce drought tolerance, as plants growing under higher CO2 levels in cooler conditions normally close stomata substantially as light levels fall.

"Our findings provide a much clearer picture of how future climate conditions will affect one of the world's most important crops," said Caine.

He noted that they aim to discover what's happening inside the plant further to understand the molecular mechanisms that govern how stomata on different wheat leaf surfaces respond to a combination of rising CO2 concentration and heat waves.

"If we can understand this, we may be able to adjust stomatal performance to optimise how plants grow under extreme future climates," added Caine.