Warmer Nights Hurt Plant Yields

Increasing warmth at night has a dramatic, negative effect on plants.

Local scientists researching that fact shared their findings Wednesday with attendees at the North Carolina Biotechnology Center’s May Ag Tech Professional Forum.

“Every degree of increasing nighttime warmth decreases food plant yields by 10 percent,” said Colleen Doherty, Ph.D., assistant professor of molecular and structural biochemistry at North Carolina State University.

She said her research, based on experiments with rice plants in subtropical Asia, demonstrated that warmer nights disrupt a plant’s circadian clock, which determines which genes are expressed at given times.

The night temperature increase in her experiments negatively affected both the quantity and quality of the plants.

Both maximum and minimum temperatures are rising globally, Doherty noted, with the minimum, usually at night, increasing faster. “The circadian clock controls all responses in plants. It integrates environmental signals to ensure optimal timing of responses. Plants use time to turn on genes to respond or prepare for stress.”

Nighttime warming, said Adam Leman, Ph.D., a lab scientist at Research Triangle-based Mimetics, “mucks up the plant’s circadian rhythms and timing of gene expression.” In the rice experiments, which Mimetics helped Doherty’s team analyze, there was a “huge shift” in gene expression caused by nighttime heat stress -- some expressing early, some late.

“These plants aren’t supplying the right gene at the right time,” Leman said. “A subtle change (in night temperature) deregulated all of these genes. You would be hard pressed to find genes reliably expressed when they should be. Many genes are affected. It’s a global shift.”

Some of the genes sleep late like teenagers, Doherty said. Others are delayed. “If a gene is supposed to turn on at dawn and doesn’t until later, it can be hugely impactful,” Leman said.

Doherty said a Morrisville company, Metabolon, helped the researchers look at the metabolism of plants subjected to increased nighttime heat stress. In her rice experiments, only 2 or 2.5 degrees of extra warmth were applied at night. “Metabolism changed across the board,” Doherty said. “Metabolites normally peaking at dawn, now peaked at dusk in anticipation of warmer nights. That’s important, because they’re making the food you eat.”

Researchers have seen similar results in other food crops such as wheat, Doherty said. 

“These are big changes a plant has to overcome,” Leman said. Fully understanding the changes affecting the tens of thousands of genes in plants “isn’t something we will figure out all at once,” he added.” It needs a lot of work.”