Species Interactions Are The Hidden Key To Understanding Non-native Plant Impacts

New research published in the journal Science shows that non-native plants interact differently with insects and soil microbes than native plants, which has dramatic consequences for carbon cycling.

Carbon cycling is the process by which plants take carbon out of the air, and then transfer it to the soil, where animals and microbes release it as carbon dioxide (CO2). For decades, scientists have assumed that the high abundance and unique traits of non-native plants explained how they increased carbon cycling where they invaded. Now, Dr Lauren Waller and colleagues from the Bio-Protection Research Centre, show that it is the different interactions that these plants form with herbivorous insects and soil microorganisms that drive their impacts.

“All organisms interact with others, and the interactions we see today have been shaped over evolutionary timescales,” says Dr Waller. “When exotic plants arrive in a new place they interact very differently with their new neighbors, such as insects and microbes.”

Humans have been transporting plants across countries and continents for centuries. So many of these have become invasive that New Zealand now has more invasive plants than native.

Between 2016 and 2019, scientists from six international research organisations and universities conducted an experiment of unprecedented scale, looking at how these plant invaders and their associated insect herbivores and soil microorganisms affect carbon cycling.

The scientists created 160 experimental plant communities, with different combinations of native and non-native plants. They then studied how those plants interacted with insect herbivores and soil microorganisms.

The results were dramatic, with non-native plants’ interactions with herbivores and soil microorganisms resulting in 2.5 times as much CO2 being released from the soil compared to native plants.

Many of New Zealand’s non-native plants grow faster than natives, which means they can store carbon more quickly. However, the same traits that allow faster growth also support microorganisms that return CO2 to the atmosphere at a faster rate.

“We were amazed to discover that novel interactions among non-native plants, herbivores, and soil microorganisms were the strongest drivers of carbon losses from soil into the atmosphere,” says co-author Dr Warwick Allen, also of the Bio-Protection Research Centre.

“We believe the increased release of CO2 from soil was driven by the higher quality and quantity of non-native plant leaves,” says Dr Waller. “These were more palatable to insect herbivores, and sped up rates of decomposition by soil microorganisms such as bacteria and fungi.”

Besides providing scientific advances in clarifying the mechanisms responsible for the effects of non-native plant invasions on carbon cycling, the study also brings insights for decision making in ecosystem restoration.

“There are many ongoing initiatives focused on nature-based solutions to fight climate change and restore ecosystems at a large scale – e.g. Plant for the Planet and Trillion Trees. Our research highlights that such approaches should consider how planted species will interact with other organisms as these can have further implications for carbon cycling,” said Dr Waller

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