What lies beneath Roots as drivers of landscape pattern in South Africa

We usually think of plants strutting their stuff aboveground: showy flowers, fragrant blossoms, and unusual shapes abound. Their underground development, however, is equally magical.

"For the final 400 million years, since plants occupied land, or roots have been the true engine of terrestrial nutrient cycling," says Mingzhen Lu, SFI Omidyar Fellow and lead author of a new study posted in Proceedings of the National Academy of Sciences. "Roots are the building blocks of biodiversity."   

Lu and his international collaborators, including scientists William Bond (University of Cape Town) and Lars Hedin (Princeton University), dug deep into the study to better understand one of the world's most unique root systems.

The researchers conducted a four-year manipulated experiment to investigate the stark distinction between the Fynbos and Afrotemperate Forest biomes in South Africa's western cape. Fynbos, a shrubby biome with high plant diversity, borders Afrotemperate Forest, a woodland dominated by a few tree species. The unusual biome boundary is so narrow that one can walk from hot, open shrubland into the cool, mossy shade of the forest in just a few steps.

The sharp distinction is accentuated by the fact that the two biomes share underlying geology and are subject to the same climatic patterns – they exist as alternative stable states. In the face of severe disturbance, the biomes may shift to reflect neighboring plant communities.

"Some systems, like water and ice, can exist in multiple states," Hedin explains. "This makes them particularly interesting as models for dramatic change because they can transition from one state to another, which is especially important in a world stressed by climate change."

The study revealed two significant findings against this backdrop. First, the root traits of Fynbos and Afrotemperate forests differed significantly. Second, the Fynbos plant community can deter trees by limiting belowground nutrient availability. Fynbos plants, in particular, repel invasion with the thinnest roots ever discovered.

"We discovered that these roots are the thinnest of all across the world's ecosystems," says Lu. "It's fascinating to see microscale plant traits like root thickness linked to macroscale emergent ecosystem patterns," Lu says.