Tree ferns turn their dead leaves into new roots

Plant biologists have discovered a unique survival strategy used by a tree fern species that is exclusive to Panama. The experts found that Cyathea rojasiana repurposes its own dead leaves, transforming them into root structures to nourish itself. 

The research, led by Professor James Dalling of the University of Illinois Urbana-Champaign, redefines our understanding of plant adaptation and survival.

Zombie leaves 

The strategy involves the reanimation of dead leaf fronds of C. rojasiana. These “zombie leaves” play a critical role in the plant’s survival. 

Once the leaves die and fall to the ground, they undergo a transformation. They reverse the flow of water and nutrients, drawing nitrogen and other vital substances from the soil back into the mother plant.

Unique strategy 

Professor Dalling and his team stumbled upon this surprising discovery while studying a different plant in a Panamanian forest reserve. 

The researchers noticed something unusual about the fronds of the tree fern. Embedded firmly in the soil, these fronds had sprouted rootlets, forming a network that was actively extracting nutrients from the ground. Laboratory analyses confirmed this unique nutrient absorption method.

Repurposing of tissue 

What makes the discovery even more extraordinary is the deceptive appearance of the reconfigured fronds. They retain the look of decayed plant matter, which likely contributed to this phenomenon going unnoticed by generations of plant biologists. 

This repurposing of dead tissue to feed the original plant is a first-of-its-kind finding in the plant world.

Adapting for survival

The evolutionary origins of this unique adaptation can be traced back to the Jurassic period, from which C. rojasiana descends. Professor Dalling suggests that the adaptation is likely a response to the nutrient-poor volcanic soils of Panama. 

“Panama is a land bridge between North and South America that coalesced 7 million years ago out of an archipelago of islands, and those islands are the result of volcanic activity in the past,” said Dalling. 

“In one site we discovered, a layer of volcanic ash several meters deep looks like sand that you would dig up on a sandy beach. The plants that grow there are distinct from those that we find elsewhere in that forest reserve.”

Searching for nutrients 

The patchiness of the vegetation means soil nutrients also are unevenly distributed. “And so the tree ferns seem to be putting out tentacles to sample the surrounding soils,” said Dalling. 

“They’re able to sample a greater range of nutrient environments for the same amount of investment of rootlets than if they just sent out a single rooting structure all around the fern. I think it’s all about the economics of how they use resources in a patchy environment.”

Extraordinary adaptations

The tree ferns also grow very slowly. “They’re probably putting on one or two leaves a year, and so they’re adding on the order of a few centimeters of height a year,” said Professor Dalling.

Each frond represents a significant investment for the plant, which it then repurposes after the leaf’s death. The slow growth rate also means that the ferns remain relatively short, with a maximum height of about two meters. This height allows the dead fronds to droop to the ground, facilitating their transformation into rooting structures.

Professor Dalling, who also serves as a research associate at the Smithsonian Tropical Research Institute in Panama, highlights this discovery as “another example of the extraordinary diversity of plant adaptations that exist in resource-poor environments.” 

The study is published in the journal Ecology. 

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