Moss has long been regarded as unusual among land plants for its resilience and apparent independence from fungal partnerships, which are common in other species. However, new research from UC Riverside indicates that this view may not apply in desert environments.

An Unexpected Partnership

More than 85% of land plants form relationships with fungi that exchange soil nutrients for sugars, and approximately 75% of these plants specifically associate with arbuscular mycorrhizal fungi, or AMF, which require a host to survive. Moss was considered the exception. All 10,000 known species were believed to exist without such fungal partnerships.

“That’s been the model,” said Jason Stajich, a UCR professor of microbiology and plant pathology and co-author of the study, published in New Phytologist. Mosses, he explained, simply didn’t need fungi. Recent findings now challenge that assumption.

Chasing Moss Through 100-Degree Heat

To investigate this, UCR doctoral researcher Kian Kelly collected samples from the Mojave and Sonoran deserts, focusing on biological soil crusts. These crusts contain complex communities of fungi, bacteria, algae, moss, and microscopic animals that stabilize desert soils. The team wanted to know whether desert mosses host different fungal communities than mosses in milder environments. “Sometimes I couldn’t find the same species of moss,” Kelly said of the search.

The team then processed moss samples and sequenced their DNA in the laboratory. They identified fungal genetic material, including AMF, which are typically unable to survive without a host plant. Furthermore, the fungal species present in desert moss differed from those found in moss from less extreme climates and from fungi in the surrounding soil. “We suspect that certain fungi are more helpful for surviving hotter, drier climates,” Kelly noted.

This mismatch made simpler explanations, such as contamination or fungi decomposing dead tissue, less likely. The evidence suggested a more specific association.

Unexpected Structures Inside Moss

Since DNA evidence alone could not confirm that fungi were living within moss tissue, Kelly stained samples with a dye that binds specifically to fungal cells and examined them under a microscope. He observed branching structures located inside the moss. “As soon as I saw that, I knew we had something really interesting,” Kelly said.

The structures resembled arbuscules, small, tree-shaped structures that fungi typically form within plant roots to facilitate nutrient exchange. Since moss lacks traditional roots, these structures were observed in the moss leaves. The researchers therefore refer to them as “arbuscule-like” rather than identifying them as true arbuscules. Whether nutrient exchange actually occurs between fungus and moss remains unconfirmed and will be the subject of future investigation.

Potential Implications

If this relationship is confirmed, its significance extends beyond desert ecology. Mosses belong to one of the oldest surviving lineages of land plants, which first colonized terrestrial environments approximately 470 million years ago. A fungal partnership present in moss tissue today could represent a remnant of the original alliance that enabled plants to adapt to life on land.

There are also more immediate implications. Biological soil crusts are fragile, and even small disturbances can take decades to heal. These ecosystems are increasingly threatened by rising temperatures and human activity. If fungi help desert moss survive heat and drought, understanding this relationship could guide future efforts to restore degraded soil crusts rather than merely documenting their decline. For now, the main conclusion is that moss, once thought to be independent of fungal associations, may have been getting help the entire time.

“The desert is full of things people overlook. Sometimes, the biggest surprises are the ones growing quietly beneath our feet,” Kelly concludes.

Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds an MBA, a Bachelor of Science in Business Administration, and a data analytics certification. His work focuses on breaking scientific developments, with an emphasis on emerging biology, cognitive neuroscience, and archaeological discoveries.

The evolution of land plants about 450 million years ago altered many of Earth’s geologic processes, like weathering and erosion. Due to the lack of evidence for meandering rivers before then, past scientists hypothesized that plants could have caused straight rivers to meander. However, in recent decades, researchers have challenged this idea. They’ve suggested that plants could have changed rivers without causing them to meander.

To understand how vegetation changed rivers in the past, researchers recently studied 49 modern meandering rivers. They sorted these rivers into 3 categories – vegetated, unvegetated, and semi-vegetated – by analyzing color images taken of them from the air. They identified 18 vegetated rivers located in South America, 24 unvegetated rivers in the western United States, and 7 semi-vegetated rivers in China and the Eastern United States. 

To examine the impact of plants on these rivers, the researchers quantified how much each river channel curves, known as its sinuosity. They used opposite banks of each river bend to find its center point, then, using digital maps, drew a line along the river’s trajectory at an equal distance between the bend center points. They used this line to calculate the angle between the river’s curve and the center point. This angle, called the migration angle, shows how a river bend relates to the river’s downstream direction. By measuring it, researchers can tell whether a river is developing more vertically or horizontally, and how sharp its bends are, either of which could be influenced by plants. 

The researchers compared migration angles across each river system to determine how river bends varied between vegetated and unvegetated rivers. They found that vegetated rivers tend to deposit sediments in the river bend, leading to curvier bends that develop horizontally and widen over time. In contrast, unvegetated rivers deposit sediment downstream, which means the rivers bend less and have greater variability in bend width.

The question remained whether plants were the primary cause of these differences or whether other factors were at play. To resolve this, the researchers investigated 3 additional factors. The first was the natural fluctuations in water flow across a river system, called its flow variability. They found that during storms, flow variability caused river bends to move downstream in unvegetated rivers, but not in vegetated rivers. This result suggested that flow variability alone didn’t drive downstream migration, although it can directly impact vegetation. 

The second variable the researchers analyzed was the amount of sediment a river can carry, or its sediment flux. They found that rivers carrying more sediment can erode more banks, also shifting river bends. However, rivers with more sediment but the same level of plant coverage had statistically similar bend angles. Thus, the researchers concluded that sediment flux alone can’t drive bend development, and that the changes were instead dependent on vegetation cover. 

The third variable they analyzed was riverbank strength. The researchers observed rivers with strong banks, made of rock or compacted sediment, and weak banks, made of loose sediment. They observed no difference in river bends with the same vegetation cover but different bank strengths. The researchers concluded that bank strength is also not the primary driver of bend migration in vegetated or unvegetated rivers. 

Of the 4 variables the researchers examined – flow variability, sediment flux, bank strength, and vegetation cover – vegetation cover consistently had the greatest impact on the appearance of meandering rivers. They concluded that meandering rivers could have existed before plants, but would have looked different. Like modern unvegetated rivers, ancient meandering rivers likely had lower-angle bends. As plants evolved and grew on river banks, the bends would have developed differently, becoming curvier like modern vegetated rivers. They suggested that understanding this process provides insight into life on Earth before plants evolved 450 million years ago. 

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