New study reveals hidden drivers of carbon cycling in world's drylands

Drylands, which include some of the world's most arid and semi-arid ecosystems, cover nearly half of Earth's land surface and play a central role in global nutrient and carbon cycling.

A new study recently published in Proceedings of the National Academy of Sciences and led by Arizona State University ecosystem scientist Heather Throop looks at how these vast regions process dead plant material — the leaves, stems and branches that fall to the ground each year.

While the breakdown of dead plant material has been studied and documented in wetter climates, scientists have struggled to characterize the same process in dryland ecosystems.

One longstanding issue specific to drylands is the vast, open spaces between plants. Most related studies in the past have focused solely on these bare areas. However, this new research shows that such sampling choices can dramatically underestimate the amount of plant material in the landscape and the rate at which it decomposes.

During their field investigations, Throop and co-author Jayne Belnap, research ecologist at the U.S. Geological Survey, examined how dead plant material naturally redistributes across drylands. Instead of being spread evenly, wind and water routinely gather leaves and branches into small, concentrated pockets. These areas are rarely sampled but turned out to be key zones where decomposition is far more active than expected.

"Deserts are often described as uniformly barren, but this study reminds us how varied and dynamic deserts are," said Throop, who is a professor in Arizona State University's School of Earth and Space Exploration and the School of Life Sciences. "Really, they are better described as an ocean with many small islands. Dead plant material accumulates in these islands, fueling the organisms that use the energy and nutrients released by decay."

What the team ultimately discovered is that the subtle ways landscapes collect and concentrate dead material shaped by microtopography, erosion and surface structure have significant effects on decomposition rates and nutrient cycling.

To conduct their analyses, Throop and Belnap surveyed variations in dryland sites and documented how plant litter accumulated across different landscape features.

"Once again, it's the little things that matter: the small parts of the landscapes we can't see or we regard as inconsequential, when added to the equation, are found to actually drive the whole show," said Belnap.

The study highlights the spatial diversity of drylands, and less focus given to those pocket regions has led to lower estimates of decomposition across these ecosystems. By taking in the full range of micro-landscapes, rather than just the open spaces between plants, scientists can better understand how nutrients and carbon move through drylands.

"We find that we can't understand deserts as a whole if we look just at the most common locations. We have to understand the biology that is happening in the little spaces that we might overlook at first glance," said Throop.

The findings show that future research that accounts for spatial diversity in dryland landscapes is essential for understanding how drylands operate.

This research is funded by the National Science Foundation.