Climate change and intensive agriculture not only affect nature above the earth – there are also problems in the soil, as a study reveals. Accordingly, the decomposing small animals in the subsurface become smaller when the temperatures rise. Agriculture, on the other hand, reduces the density of these soil animals. Both of these factors cause the decomposition of organic material in the soil to decrease – and with it the nutrient recycling that is important for all ecosystems.
An army of tiny “service providers” works largely unnoticed and in secret: countless small insects, arachnids and other soil creatures are tirelessly busy decomposing dead plants and other organic material and recycling the nutrients contained therein. They form the basis for plant growth and the functioning of the above-ground ecosystems.
Double burden on the underground environment
But this very important underground world is under increasing pressure – in two ways. On the one hand, climate change is causing rising soil temperatures and increasing drought. On the other hand, intensive land use also affects soil organisms. Studies show that the underground biodiversity decreases through the use of fertilizers and pesticides, through plowing and mowing and also through the conversion of grasslands into fields. However, these negative effects can be mitigated, at least in part, by ecological, soil-conserving management of the land – this is also borne out by observations.
The problem, however, is that many areas in Germany and elsewhere have to cope with both negative influences at the same time – climate change and land use. How this double impact affects and whether they have the same consequences on soil animals has so far been unknown, as Rui Yin from the Helmholtz Center for Environmental Research in Halle and his colleagues explain. That is why they have now examined this in more detail in an ecological test facility using the example of soil-living microarthropods such as mites and springtails. In the facility, they put differently managed arable and grassland test areas to a simulated future climate: 0.6 degrees higher temperatures, ten percent more precipitation in autumn and spring, but 20 percent less rain in summer.
Climate change makes soil animals smaller
It turned out that both simulated climate change and intensive land use led to a significant decline in soil-living microarthropods. Their biomass decreased by 17 percent on areas with climate change, and by 37 percent on intensively cultivated arable land compared to grasslands. The surprise, however, is that although this shrinkage of soil-dwelling biomass occurred under both stressful conditions, the causes for it were very different and independent of one another, as Yin and his colleagues report. Artificial climate change caused the individual arthropods to shrink by around ten percent.
The researchers explain this because, on the one hand, a small body size makes it easier to give off excess heat – which is why tropical animals are often smaller than their relatives in the cold polar regions. In warm animals such as mites and insects, their metabolism and development take place more quickly at higher temperatures. “This creates new generations more quickly, which then remain smaller,” explains Yins colleague Martin Pestler. “Presumably, not only will smaller species prevail, but also smaller individuals within the same species.”
Organic farming cannot compensate for the climate change effect
Intensive agriculture, on the other hand, had a completely different consequence: it was not the size of the heavily cultivated arable land that decreased, but the number of microarthropods in the soil. The scientists found around 47 percent fewer mites and springtails in the soil of these arable land than under the hardly used grasslands. “The exciting and sobering thing about it is that the effects of climate and use hardly influence each other,” says Schadler. However, this means that even if you change agriculture in such a way that the soil is managed carefully and ecologically, this helps to prevent the density of soil animals from decreasing. But the negative effects of climate change cannot be offset.
“So not everything that threatens to break down due to warming can be saved by environmentally friendly land use,” says Schadler. In order to mitigate the consequences of climate change, one has to start directly with greenhouse gases – as quickly as possible. “We cannot rely on something else to come up with,” warns the researcher.
Source: Helmholtz Center for Environmental Research – UFZ; Technical article: eLife, doi: 10.7554 / eLife.54749