The Mojave Desert’s Joshua trees look timeless, but their future isn’t guaranteed. Despite being built for heat and drought, these long-lived yuccas are already showing signs of stress as temperatures rise and dry spells lengthen. Fewer young trees are making it past their first years, and the species’ range appears to be shrinking. 

A new study led by a multi-institution team that includes University of Connecticut ecologist Karolina Heyduk asks a simple, crucial question: how much wiggle room do Joshua trees have to adapt? The answer points to a surprising ally – how they breathe at night.

Joshua trees in a warming climate

Most plants throw open microscopic pores on their leaves during the day to take in carbon dioxide for photosynthesis, but that comes with a cost: precious water escapes while the sun is blazing. 

Some desert specialists dodge that trade-off by using a different playbook, called crassulacean acid metabolism, or CAM. CAM plants take in CO₂ at night when it’s cooler and stash it away until daylight returns to power sugar production.

“We sort of stumbled upon this idea that Joshua trees might use CAM photosynthesis,” Heyduk said. “Finding evidence of CAM in Joshua trees is great news – it may help the plants tolerate the warming climate across their range.”

Common gardens, uncommon insights

To see whether all Joshua trees play by the same rules – or whether some populations are naturally better tuned to today’s harsher conditions – the team established common garden test plots.

The researchers grew seedlings from populations across the species’ ranges, including both recognized species, Yucca brevifolia and Yucca jaegeriana, side by side under the same conditions. That setup strips away local weather and soil differences, letting genetic and physiological differences rise to the surface.

As the seedlings grew, the researchers tracked growth, water use, leaf gas exchange, and the chemical signatures that reveal when and how carbon is taken up. 

The patterns were clear: many seedlings showed nighttime CO₂ uptake consistent with CAM, and the intensity of that CAM-like behavior varied among populations. 

In other words, Joshua trees appear to have some built-in flexibility in how they photosynthesize, and some lineages lean into the night-shift strategy more than others.

Genes back up the physiology

The team didn’t stop at leaf measurements. They looked under the hood – profiling gene activity and the metabolites plants stockpile when they run CAM. 

“We’re bridging a lot of fields in biology,” Heyduk said. “We measured a lot of physiological traits, but we also looked at the gene expression of these plants in the gardens, and the accumulation of metabolites.” 

The timing of gene activity matched expectations for CAM, bolstering the case that Joshua trees can switch – or at least blend – between daytime and nighttime carbon uptake. 

The two species also differed in how they process carbon and nitrogen, hinting at deeper physiological distinctions that may help explain why both persist as separate lineages despite overlapping ranges and occasional hybrids.

Why this matters for conservation

If CAM capacity is real and variable, it could be a lifeline. Nighttime carbon uptake reduces water loss, a critical edge as the Mojave gets hotter and, importantly, as nights warm too. 

But flexibility is only half the story – longevity complicates the rest. A mature Joshua tree can live for centuries; some living trees have experienced the entire arc of industrial-era climate change. The seedlings trying to establish today face a very different climate than the one their elders grew up in.

“We’re not focusing on desert species quite as much as other ecosystems,” Heyduk said. “I think partially that’s because we think they’re already adapted to the super-hot environment and they’ll be fine.”

“However, the deserts are getting hotter, and in particular the nighttime temperatures are getting hotter.” If nights stop offering relief, even CAM users may struggle.

Heat and Joshua tree survival

One red flag is the lack of young trees. Fewer seedlings are making it to sapling stage, suggesting a new bottleneck right where populations renew themselves. 

To test how temperature – especially warmer nights – affects survival, the team is now growing seedlings under tightly controlled conditions, dialing nighttime temperatures up and down to see how water use, growth, and CAM behavior respond.

The goal is to pinpoint whether hotter nights are tipping the balance, and which populations cope best.

“What today’s seedlings are experiencing is going to be very different from what they might experience in 100 years when they’re mature plants,” Heyduk said. “We need to understand how they will respond to that change.”

A collaborative blueprint for action

This project is as much about method as it is about the Mojave. University researchers, federal scientists, and teams from primarily undergraduate institutions pooled fieldwork, greenhouse trials, physiology, genomics, and metabolomics.

That breadth matters because it lets scientists connect genotype to phenotype – tying genetic differences to real-world traits that influence survival.

The immediate conservation takeaway is practical: not all Joshua tree populations are the same. Some may harbor greater CAM capacity or other physiological tweaks that make them better bets in a warming desert. Identifying and prioritizing those lineages – while protecting the habitats they occupy – could buy the species time.

Joshua trees won’t outpace climate change by migrating quickly; they don’t disperse far, and they don’t grow fast. But if they can lean on a night-shift photosynthesis strategy – and if we focus protection on the populations best at it – they may have a fighting chance to hold their ground as the Mojave’s thermostat keeps climbing.

The research is published in the journal the New Phytologist.

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