The study is published in the journal Global Change Biology.
Drought has the greatest impact on soil invertebrates
The scientists examined the effects of changes in precipitation on soil invertebrates. Their results show that droughts reduce the number of soil invertebrates by approximately 35%, while increases in rainfall lead to similar increases in invertebrate populations. The impact of drought is not uniform across all invertebrates. “The groups most affected include many species that help improve soil health by breaking down dead leaves and storing the remaining organic material in the soil,” said Sebastiaan Luyssaert. According to the researchers, the relationship between body size and response to precipitation makes it easier to predict future responses of soil biodiversity to climate change.
59% of all life is in the soil
Soils are home to an astonishing 430 million species, more than half of all species found on earth: 90% of the world's fungi, 85% of plants and more than 50% of bacteria - and 59% of life overall. While we know a lot about how threats like climate change affect biodiversity aboveground, little is known about how they affect animals in the soil.
“Our findings will help us predict future responses of soil invertebrates to climate change more accurately, as well as the potential consequences of this on soil functioning and health. In the long term, these changes could potentially threaten forest health and their ability to provide ecosystem services like nutrient cycling,” said Phil Martin, applied ecologist at BC3 in Spain and lead author of the study.
Differences due to diet and physical adaptations
The differences in response among various invertebrate groups are likely due to two factors: diet and physical adaptations. According to the study, many of the species most affected by drought feed on plant roots, dead leaves, or fungi and bacteria in the soil — all sources that can diminish due to drought. Meanwhile, smaller soil organisms are less capable than larger ones of moving to moister areas within forests and are thus at greater risk of drying out.
“Soil moisture is a key limiting factor for soil fauna, and over time these animals evolved a wide range of ecological, morphological and physiological adaptations to specific precipitation regimes. However, the large changes in precipitation regimes that we are currently experiencing cause both direct and indirect effects on soil fauna, as some of them become less adapted to altered food resources or more susceptible to predation,” said Mathieu Santonja, soil fauna ecologist at Aix Marseille University and co-author of the study.
Photo: Solène Brasseur