Los Alamos National Laboratory research examines how piñon and juniper trees manage water

Scientists still have new leaves to turn over when it comes to understanding tree mechanics, as demonstrated by a recent study from Los Alamos National Laboratory, which found some plants may react differently to drought than previously believed.

“Plants cannot run away if things change. But they actually are pretty adaptable, and we know very little about the adaptability and how they can actually manage situations,” said Sanna Sevanto, a LANL scientist and one of the study’s authors.

The big takeaway from the study published in the journal Nature this May is that plants have more ability to adjust when they close their pores — called stomata — than previously thought. That means environmental conditions like rainfall may play a bigger role in how much water plants release than previously believed and could be good news for long-term predictions of plant survival under drier conditions.

“This was one of those surprise findings that you encounter by accident while looking for an answer to another problem,” said Turin Dickman, another study author and LANL scientist. “By putting the pieces together from a number of incidental findings, we came up with a new way to think about an old concept.”

Some plants, like juniper, are classified as anisohydric, meaning they can adjust how much water they release through their leaves depending on weather conditions like monsoons or drought. Plants like piñon pine are called isohydric, meaning scientists believe they release a similar amount of water regardless of environmental conditions.

Los Alamos National Laboratory scientists looked at how piñon pines and juniper trees respond when they get an influx of water. When piñon pines were given excess water followed by a subsequent period with no water, they were able to keep their pores open longer during the dry period.

Plants control how much water is released via pores on their leaves. When the pores open, plants take in carbon dioxide — the energy source they use to make food — and release oxygen and water. Closing the pores helps a tree retain more water, but opening the pores allows a plant to gather more carbon dioxide reserves, the fuel it needs for photosynthesis.

In the arid New Mexico environment, even on moist days it can get dry enough for piñon pine trees to close their pores in the afternoon to preserve moisture. That limits the trees to doing photosynthesis in the morning.

“But what we are showing in this paper is that if the conditions have been good enough, then they may not need to close their stomata in the afternoon,” Sevanto said. “Their tissues can tolerate that afternoon dryness, and that gives them an overall bigger carbon intake for the day.”

The research indicates that piñon pines could be more resilient to drought following extremely wet periods. A 2013 study predicted piñon pine forests could be gone from the Southwest by 2050 because of drought. But the new research on stomatal closure points makes Sevanto hopeful.

The study shows that during moist years, “piñon pine might have more capacity to rejuvenate itself and still become more resilient than we thought,” she said.

While scientists were able to observe this phenomenon in piñon pine, Sevanto would like to find out exactly how the trees lower their stomatal closure point and see if the same phenomenon can be observed in other trees.