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DATE: July 28, 2020

SNIP: Today, life in the soil must contend with several problems at once. The biomass of small animals that decompose plants in the soil and thus maintain its fertility is declining both as a result of climate change and over-intensive cultivation. To their surprise, however, scientists from the Helmholtz Center for Environmental Research (UFZ) and the German Center for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig have discovered that this effect occurs in two different ways: while the changing climate reduces the body size of the organisms, cultivation reduces their frequency. Even by farming organically, it is not possible to counteract all negative consequences of climate change, the researchers warn in the trade journal eLife.

Largely unnoticed and in secret, an army of tiny service providers works below our feet. Countless small insects, arachnids and other soil dwellers are indefatigably busy decomposing dead plants and other organic material, and recycling the nutrients they contain. However, experts have long feared that these organisms, which are so important for soil fertility and the functioning of ecosystems, are increasingly coming under stress.

On the one hand, they are confronted with the consequences of climate change, which challenges them with high temperatures and unusual precipitation conditions with more frequent droughts. On the other hand, they also suffer from over-intensive land use. If, for example, a meadow is turned into a field, soil animals find fewer niches and food sources there. Intensive plowing, mowing or grazing, as well as the use of pesticides and large amounts of fertilizer also have a negative effect. But what happens when soil life is faced with both challenges at the same time?

The examined specimens on the areas with higher temperatures and changed precipitation were on average about ten percent smaller than on the comparable areas with today’s climate. Biologists have so far been familiar with such connections between body size and climate primarily in larger animals. For example, bear species in warm regions of the Earth are significantly smaller than the polar bear found in the Arctic. This is due to the fact that a small body has a comparatively large surface area over which it can release heat—which is an advantage in the tropics, but easily leads to cooling in polar regions. In poikilothermal animals such as insects, high temperatures also stimulate metabolism and developmental speed.

According to the experiment, over-intensive land use can also trigger a very similar effect. This is because the biomass in the soil also decreases as a result. [A]round 47 percent fewer mites and springtails lived on GCEF plots cultivated conventionally compared with plots extensively used as meadows.

Until now, many experts had hoped that eco-friendly agriculture could offer some kind of insurance against the negative consequences of climate change. Yet when it comes to maintaining the performance of soil animals, this strategy does not seem to work: changes in temperature and precipitation reduce their biomass regardless of cultivation.