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Biodiversity does not just protect what we see above ground, it also helps safeguard the hidden world beneath our feet. Researchers at Utrecht ľ�ϸ���Ӱ�� found that during drought, areas with a higher number of plant species maintained higher activity of detritivores, the small creatures that break down dead organic matter in the soil. The , published today in the scientific journal Global Change Biology, is the first publication based on data collected in the long-term Utrecht ľ�ϸ���Ӱ�� Biodiversity and Climate Variability Experiment (UU BioCliVE).

Climate change increases the frequency of extreme weather, such as droughts. While it has become clear that higher plant diversity helps ecosystems withstand and recover from extreme weather, it remained unclear how plant diversity affects the activity of detritivores during drought.

“When looking at the soil, researchers often focus on micro-organisms,” says PhD-candidate and first author of the study Shengnan Wang. “But how the activity of detritivores in the soil is affected by plant diversity and climate change, is something that has remained largely overlooked.”

These soil creatures, animals such as earthworms, nematodes and potworms are vital for healthy ecosystems. Ecologist Yann Hautier: “By feeding on dead organic matter, such as fallen leaves, they help recycle nutrients and maintain soil fertility.”

As climate extremes become more common, preserving plant diversity could be key to keeping ecosystems stable and resilient.

Controlled precipitation

BioCliVE consists of 352 containers, each filled with 1000 liters of soil. In these containers, grassland ecosystems were constructed that represent a gradient of biodiversity. The containers either contain one, four, eight or twelve species of grasses and forbs.

Hautier: “All containers are housed underneath a glass roof that is open most of the time but closes when it rains. So the setting is as natural as possible, but we can still control the amount of precipitation the containers receive.”

Activity at different depths

This way, the team of researchers was able induce a drought in the grassland ecosystems. This allowed them to compare how active detritivores were at different soil depths after a drought, with their activity under normal conditions based on historical rainfall data.

“We used long strips of PVC to measure activity, which we stuck into the ground,” Hautier explains. “The strips have sixteen holes in them, and these holes are filled with a substrate. If invertebrates in the soil feed on the substrate, you see an empty hole. By looking at which depth the holes were empty, we could measure at which depth the animals were active.”

Deeper in the ground

The researchers found that plant diversity increased the feeding activity of detritivores under both control and drought conditions. Moreover, during drought, the positive effects of plant diversity on feeding activity increased with depth.

“Under drought, the benefits of higher plant diversity on feeding activity seems to be maintained, as high feeding activity can still be observed in deeper ground,” says Wang. What caused this is unclear. “We do not know if the animals go deeper into the soil, or if there is another explanation,” says Hautier. “This is something we would like to find out in future studies.”

Clear message

But even though it is not exactly known how the activity is shifted to deeper soil layers, the results send a clear message. “Understanding how climate change alters belowground dynamics is especially important in countries like the Netherlands. Up to eighty percent of the biological community in grasslands is belowground, and grasslands cover more than a third of the country and represent fifty percent of agricultural lands,” notes Katie Barry, UU researcher and co-author of the study.

“This study shows that biodiversity is really key to buffer ecosystems against the effects of climate change,” Hautier points out. “As climate extremes become more common, preserving plant diversity could be key to keeping ecosystems stable and resilient.”

Acknowledgements and funding

BioCliVE is made possible by a large group of people, Including two technicians, numerous PhD, MSc, and BSc students, as well as staff members from the Ecology and Biodiversity research group.. BioCliVE is funded by the Ecology & Biodiversity group, the Department of Biology of Utrecht ľ�ϸ���Ӱ�� and the Utrecht ľ�ϸ���Ӱ�� Fund. The project received financial support from the trusts and foundations attracted by the Utrecht ľ�ϸ���Ӱ�� Fund: K.F. Hein Fonds, WNF INNO-Fonds, Ars Donandi, Stichting Thurkowfonds, M.A.O.C. Gravin van Bylandt Stichting. Shengnan Wang was funded via the China Scholarship Council (CSC).