Rising temperatures alter photosynthesis and plant growth

A new study reveals how climate change is affecting plant growth beyond the effects of rising CO2 levels. The researchers found that rising temperatures are impacting photosynthesis and plant viability.

The experts report that excessive heat reduces the efficiency of enzymes that drive photosynthesis and can hinder plants’ ability to regulate CO2 uptake and water loss. They explain that certain aspects of a plant’s structure can make it more or less susceptible to heat stress.

Features of the ecosystem, such as the density of plants or local atmospheric conditions, also influence how crop yields will respond to heat.

Study co-lead author Caitlin Moore is a research fellow at the University of Western Australia and an affiliate research fellow at the Institute for Sustainability, Energy, and Environment at the University of Illinois Urbana-Champaign. 

“It’s important to have an understanding of these issues across scales – from the biochemistry of individual leaves to ecosystem-level influences – in order to really tackle these problems in an informed way,” said Moore.

According to study co-author Professor Carl Bernacchi, there has been a lot of focus on rising CO2 and the impact that it has on plants. “And it is an important factor, because we are changing that carbon dioxide concentration enormously. But it’s a small part of the bigger story.” 

“Once you throw changing temperatures into the mix, it completely messes up our understanding of how plants are going to respond.”

“Take Rubisco, the key enzyme that fixes carbon dioxide into sugars, making life on Earth possible,” said study co-lead author Amanda Cavanagh. “Rubisco speeds up as the temperature increases, but it’s also prone to making mistakes.”

Instead of binding CO2 to sugars, Rubisco sometimes fixes oxygen, initiating a different pathway that wastes a plant’s resources. Higher temperatures make this more likely, said Cavanagh. The enzyme will begin to lose its structural integrity and become increasingly ineffective. Heat can also compromise a plant’s reproductive capacity. 

When temperatures are too warm, plants open up pores on their leaves called stomata to cool themselves. The stomata also allow plants to absorb CO2, but when they are fully open, the leaves can lose too much moisture.

“Temperature affects the atmosphere above the plant,” said Moore. “As the atmosphere heats up, it can hold additional water, so it’s pulling more water from the plants.”

Cavanagh, who studies the molecular biology of plants, said some plants are more heat tolerant than others, and scientists are searching their genomes for clues to their success.

“For example, you can look at wild Australian relatives of rice that are growing in much harsher climates than most paddy rices. And you see that their enzymes are primed to work more efficiently at hotter temperatures.”

One goal is to transfer heat-tolerant genes to rice varieties that are more susceptible to heat stress.

“The world is getting hotter at a shocking rate,” said Cavanagh. “And we know from global models that each increase in gross temperature degree Celsius can cause 3% to 7% losses in yield of our four main crops. So, it’s not something we can ignore.”

“What makes me optimistic is the realization that so much work is going into globally solving this problem.”

The study is published in the Journal of Experimental Biology.

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By Chrissy Sexton, Earth.com Staff Writer