Growing up on the Tundra

Cottongrass is one of the taller tundra species increasing in abundance as temperatures warm.

Anne D. Bjorkman

Tundra is the most rapidly warming biome on Earth. Understanding how this change physically affects tundra plants is crucial to predicting ecosystem functioning and feedbacks that affect future climate. In a recently published study, an international team of 129 scientists analyzed a massive dataset from 117 Arctic and alpine tundra sites to determine how tundra plant characteristics change over space and time, depending on temperature changes and moisture conditions.

Lead author Anne Bjorkman, a postdoctoral researcher now at the Senckenberg Biodiversity and Climate Research Centre in Frankfurt, Germany, and ecologist Isla Myers-Smith at the University of Edinburgh, merged existing tundra plant research teams and assembled new data with collaborators working at sites throughout the tundra biome to create a greatly expanded plant trait database. The study analyzed over 56,000 plant trait observations from 1,520 plots recorded across three decades. Traits such as adult plant height and leaf area characterized size, while nitrogen and dry matter contents in leaves were traits that tracked how plants absorb and allocate nutrients and capture sunlight.

The researchers found that plant height was the only trait that increased rapidly over time. These changes largely reflected geographic shifts in species composition, including species spreading outward from warmer microclimates within tundra landscapes. Additionally, soil moisture was shown to have a stronger than expected effect. In dry sites, leaf area and leaf nitrogen content decreased with warmer temperatures, but in wetter sites, the reverse was true; those traits increased with warmer temperatures.

“There’s an assumption that high latitude, northern systems are warming and that should be what’s driving the change that we see in these systems,” says co-author Myers-Smith. Instead, these findings add to others, indicating that soil moisture is more critical, and temperature does not tell the whole story. The results will help climate modelers project how quickly tundra ecosystems respond and contribute to or mitigate warming, since plant communities affect climate feedback systems. Taller plants could contribute to warming by trapping a thicker blanket of insulating snow or because stems poking out above snow darken the tundra surface, drawing in more heat. Warmer surface and soil temperatures could also thaw soils in summer and increase decomposition rates. But taller plants may also offset warming through increased carbon storage and shading, reducing soil temperatures and slowing decomposition rates. Which way the balance is tipped, or whether positive and negative effects cancel each other out, is a conundrum yet to be solved. (Nature)

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