Our soils filter drinking water and produces food. Soils only carry out these services, because they harbour thousands fungal and bacteria species which work together like the wheels in a clock mechanism. These are the conclusions reached by a study published in the renowned by researchers from Agroscope and the University of Zurich. To summarise their findings: the more species-rich the microbial community, the more ecosystem functions remain intact, which in turn has a positive impact on agriculture.
"This is presumably the first study that shows that bacteria and fungi in our soils are organised into huge networks, and that these networks perform crucial functions" says Marcel van der Heijden, an agroecologist at Agroscope and the University of Zurich. "The more intertwined the network is, the more our soils can do for agriculture."
In brief, the more species of bacteria and fungi that were present in the test soils, the more nutrients the plants absorbed, and the greater the number of plant species that were able to grow in them. If, however, there were only a few microorganisms in the soils, or none at all, far fewer nutrients were absorbed, and only grasses grew.
But other important soil functions - for example, nutrient efficiency, the breakdown of dead plant material and carbon sequestration from the atmosphere - are also lost when there are too few bacterial and fungal species. "Without bacteria and fungi, the Earth would look like Mars" Cameron Wagg, primary author of the study, puts it succinctly.
Like an Enormous Factory
The many species of fungi and bacteria work together like employees in a huge factory: one is responsible for ’taking delivery’, one for ’warehousing’, one for ’equipping the conveyor belts’, one for ’welding’, and one for ’cleaning the building’. The system functions best when all posts are filled" van der Heijden explains. "The fewer ’employees’ the ’factory’ has, the less it can produce."
In fact, the bacterial and fungal species occupy each post several times over. "The advantage of this is that if one species is absent, the next can simply take over" explains van der Heijden. This means that soils function better during prolonged heat waves, drought stress, or other environmental impacts.
The More Biodiverse, the More Soil Functions
For the study, the researchers reduced the biodiversity of soil samples in stages and they worked with miniature grassland in special microcosms. This allowed them to measure how much nitrous oxide the various soils produced, thereby losing valuable nitrogen. They also investigated whether the microbial networks in the soil influenced the leaching of vital nutrients such as nitrogen and phosphates. A ’system analysis’ was then conducted, and several functions were analysed simultaneously (’multifunctionality’). The results showed that the more complex and biodiverse the microbial community of a soil was, the more ecosystem functions remained intact - which has a positive effect on agriculture and the environment.
Sieving It All Away
For the study, researchers used soil samples from a field in Zurich. A series of increasingly fine sieves was used in order to reduce the biodiversity of a soil. This meant that some samples had a wide variety of bacteria and fungi, whilst others had very few or even none at all. The experts then mixed the soil samples (’inoculum’) with sterilised earth in hermetically sealed chambers in which they had sown a grass-clover-herb mixture. The chambers allowed the gas exchange to be recorded.