While antibiotics help us fight tough diseases, they leave our gut biomes in poor condition. It turns out that pesticides have a similar effect on arbuscular mycorrhizal fungi (AMF), a plant symbiont that is found in our soils and that helps plants acquire nutrients. That is what the Biodiversa-project Digging Deeper shows in its latest paper published in Nature Ecology & Evolution. Prof. Dr. Marcel van der Heijden from Agroscope and the University of Zurich and principal investigator of Digging Deeper summarises the findings of this study and their implications for European farmers and decision-makers.
Can you describe this study and why it is important?
While we have a pretty good understanding of the importance and roles of biodiversity above the ground, the consequences of biodiversity loss underground still bear many unanswered questions. We know that biodiversity declines upon intensive land use, both above and below the ground. It is also proven that biodiversity is crucial to maintaining key ecosystem functions such as soil carbon sequestration, nutrient uptake, plant yield etc.
In the Digging Deeper project, we studied whether crop diversification and changes in agricultural management can promote soil quality and its associated ecosystem services. We looked at soil samples from 210 grassland and croplands across a 3000 km North-South European gradient and studied the diversity and functioning of the symbiotic arbuscular mycorrhizal fungi (AMF). AMF are widespread plant symbionts present in soils and are especially important natural systems. We hypothesized that the more crop rotation, the more plan nutrient uptake is facilitated by AMF.
AMF play a big role in plant nutrition and are known to enhance plant biodiversity. In natural ecosystems, they can account for up to 80-90% of plant nutrient uptake. The contribution of AMF to nutrient uptake and plant growth in conventionally managed fields is still unclear. But experiments show that adding AMF to soil can increase the yield of some crops substantially, so they can also be important for plant growth in managed agricultural systems.
What are the main findings of this study? What is the novelty of these findings?
We expected the diversification of soil cover to play a major role in the diversity and functioning of AMF. We compared samples from grasslands, organically managed fields and conventional farms, and we actually found that the use of fungicides had a very strong impact on AMF diversity and functioning. The number of uses of fungicides in the field had a strong and negative effect on AMF abundance and diversity. It is the first time that this effect is consistently shown on such a big scale, over the whole of the North-South gradient in Europe.
Crop diversification has often shown to have a big impact on soil quality, AMF and yield, as varied plants offer a more diverse environment for AMF and soil life, and because resources are more efficiently utilised when different crops are grown. But besides crop diversification, our study showed that soil coverage was a more important factor to predict soil quality. Through year-round soil coverage, the symbionts in the soil can continuously access sugars from the plants, making the AMF populations stronger and better able to assist the plants in their nutrient uptake. This finding is especially interesting for organic farms that rely more on AMF for their plant growth since they have limited use of chemical fertilisers.
What effect can these findings have on the agricultural sectors?
Farmers should be vigilant with the use of fungicides and only use them when they are strictly necessary. When moving from conventional farming practices to organic farming, the rates and abundance of AMF become much higher. But it is not easy for farmers to eliminate fungicides altogether: a disease decimating their entire yield brings a bigger loss than having lower rates of AMF. However, farmers are increasingly moving towards pesticide reduction. In the EU Farm to Fork strategy, there is an ambition that “by 2030, the use and risk of chemical and more hazardous pesticides in the EU should be reduced by 50%.” This will have a positive impact on AMF and their benefits.
We also see that more and more, farmers plant so-called cover crops. These are plants that are grown after the main crops have been harvested, and are usually not used for commercial purposes. They also offer the benefits of reducing nutrient leaching and improving soil structure with their roots. However, cover crop yield is usually not sellable and there are additional costs for purchasing seeds, sowing and management. So not all farmers do this, even if it is beneficial for their soil’s health.
Policies can have a huge impact on the adoption of cover crops. In Switzerland for example, it is mandatory for farmers who harvest their crops (e.g. wheat, barley) early to plant a cover crop. Stronger policy regulations or dedicated subsidies could promote the use of cover crops and improve the soil health of agricultural land throughout Europe.
There is growing interest in sustainability and the public is receptive as well. But actions such as cover crops require additional resources and farmers that are more environmentally friendly often have a lower yield, especially in the short term, than conventional farming. This is reflected in the prices of these products and the public needs to be ready to pay a bit more for their sustainable food.
What are the next steps for this research?
The Digging Deeper project has come to an end, but we are preparing a follow-up project on the effects of climate change on soil diversity and functioning. Besides improved nutrient uptake for plants, it was shown that the symbiotic fungi could reduce crops’ risk of drought. We are also doing greenhouse experiments further studying the effects of pesticides on AMF.
What do you think is the added value of a transnational approach used in Digging Deeper, and more generally of international research programs such as Biodiversa?
If we had done our research in just one of the six countries we studied, the relevance and impact of our findings would have been much lower. Our results span the North-South European gradient, which allows us to generalise the results of the project, even if soils and climate are drastically different between Spain and Sweden, for instance.
Biodiversa also funds relatively small projects. This makes the projects easily manageable, and we can have intensive contact with all partners and researchers, while also benefiting from the specific expertise of all six countries involved.
Biodiversa also encourages the inclusion of early career researchers, and we also interacted with policy makers and with farmers. The diversity of people involved in our project enriched our perspectives and broadened our thinking spectrum. This multi-actor approach is highly relevant and interesting because we can, during our research phase, have an understanding of what information the policy-makers and farmers are after. What can be of use to them, but also evaluating the social and economic consequences of our findings.
About Digging Deeper:
While most studies on ecosystem functioning have targeted aboveground communities, a large part of biodiversity is literally hidden below ground. Thus, the consequences of soil biodiversity losses on ecosystem functioning are still poorly understood. The Digging Deeper project studied whether agroecosystem diversification (crop diversification) can promote soil biodiversity and the delivery of beneficial ecosystem services across Europe.
The Digging Deeper project was funded in the framework of the 2015-2016 Biodiversa call on “Understanding and managing biodiversity dynamics to improve ecosystem functioning and delivery of ecosystem services in a global change context”.