Plant diversity protects soils from temperature extremes

For 18 years, researchers have studied how soils react to temperature fluctuations with different types of vegetation. © Karl Kübler, Max Planck Institute for Biogeochemistry Jena

The more colorful the blanket, the more balancing it has: A long-term study shows that species-rich plant cover can protect soil ecosystems particularly effectively from harmful temperature fluctuations caused by weather extremes. The buffer effect thus significantly strengthens the resilience of grassland ecosystems against the consequences of climate change. Ultimately, this natural mechanism can also help slow global warming, say the scientists.

Where diversity can develop, nature is particularly strong: many studies have already made it clear that high plant biodiversity can promote the stability and productivity of ecosystems in a complex way. Among other things, the communities are becoming more resilient to the increasing extreme weather events caused by climate change. When researching these positive effects, however, there has so far been little focus on one potentially important component, say the scientists led by Yuanyuan Huang from the German Center for Integrative Biodiversity Research Halle-Jena-Leipzig (iDiv): “Soil temperature plays a central role in controlling important ecosystem processes related to water, carbon and nutrient dynamics, microbial activity and agricultural productivity,” says Huang. However, the extent to which plant diversity can have a stabilizing effect on soil temperature during extreme weather has not yet been systematically investigated.

On the trail of a balancing effect

Huang and her colleagues have now closed this gap with the results of an extensive long-term study. It is based on data from a large-scale grassland biodiversity experiment that spanned the period from 2004 to 2021. The test site consisted of 80 plots with different plantings: it ranged from monoculture of just one species to a mixture of 60 native plant species. The researchers also used plots that were kept free of plants as a comparison. The soil temperature was continuously recorded over the course of 18 years at a depth of five and 15 centimeters. The values ​​could be compared with the respective weather data. As the team reports, there were also some particularly hot, dry and unusually cold climate periods during this time frame.

The researchers report that the positive effect of a high level of species diversity was clearly evident in the results: the more species that formed the vegetation, the better the soil was protected from overheating in scorching heat, and in colder periods the “colorful blanket” helped particularly well, to store heat. “We were able to document that high diversity acts as a natural buffer and ensures stability in the face of climatic extremes,” summarizes Huang. Specifically, the evaluations showed that on particularly hot summer days, the soil temperature in plant communities with 60 species was on average around five degrees Celsius lower than in bare soil. In comparison, monoculture only achieved a modest cooling effect of around two degrees.

Cooling or warming as needed

As far as the effect in the cold season is concerned, it was shown that on frosty days the soil temperature in the 60-species plant community was around 1.5 degrees Celsius higher than in unplanted plots. In monocultures, however, the researchers only found a heat effect of around 0.3 degrees. The data from the long-term study also showed that the positive effects increased as the test communities got older and were particularly pronounced under the harshest climatic conditions.

Based on certain test values, the team was also able to conclude on what causes the stabilizing effect of plant diversity is based. One aspect is therefore the comparatively high total area of ​​leaf cover with species-rich vegetation, which ensures a stronger insulating effect. But a second aspect is apparently even more important: when biodiversity is high, the biomass in the soil increases due to the large number of different plant roots. This material in turn leads to less heat conduction in the upper 60 centimeters of the soil, the researchers explain.

According to them, the study results document the significant importance of stabilizing soil temperature through plant biodiversity in grassland ecosystems. The effect can therefore be crucial in mitigating the negative effects of extreme climatic events. The scientists emphasize that what strengthens these ecosystems can in turn benefit their ability to bind carbon in the soil. Senior author Nico Eisenhauer from iDiv concludes: “Our research emphasizes how important it is to maintain and promote biological diversity in our ecosystems in order to protect the environment and ensure a sustainable future,” says the scientist.

Source: University of Leipzig, specialist article: Nature Geoscience, doi: 10.1038/s41561-023-01338-5

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