title: Effects of environmental chemicals on soil and plant health
Creators: name: Caggìa, Veronica Lucia Luigina
Publisher: name: Universität Bern
Year: 2023
Subjects: subject: 580 Plants (Botany)

description: The world’s soils are threatened by intensive farming, industrial pollution, mining, and poor waste management that are poisoning them. All soils are under a lot of pressure, as 95% is used towards the production of food for human and animal consumption; consequently, and unsurprisingly this soil has extensive damage. Soil pollution is described as soils that contain toxic chemicals or elements, such as pollutants, can be present in high enough concentrations to constitute a risk for the environmental and human health. To understand environmental health more holistically – e.g., in the context of a food chain – we urgently need to understand decode the interactions of these environmental chemicals with soils, their intrinsic microbiomes as well as with their crops. Such understanding will allow to find possible solutions to reduce the negative impacts of contaminants in our food chain. Plants are extremely adaptable, despite their limited ability to move, and have developed multiple physiological strategies to tolerate and defend themselves against a vast array of external pressures and stresses. In recent years microbiomes are more and more recognized for their importance on environmental health. One hypothesis is that plants modulate their associated microbiomes to cope with and survive under soil contamination, for instance by enhancing degradation, transformation, immobilization, or safe storage. However, evidence for this phenomenon remains fragmented.
The aims of this thesis were to understand, taking a holistic One Health perspective, the microbiome-mediated chemical feedbacks on plant growth due to soil pollution. As contaminants we studied herbicides (Chapter I), arsenic (Chapter II) and the interaction between arsenic and benzoxazinoids (Chapter III). Soil herbicide contaminations were studied with glyphosate and terbuthylazine as chemical stresses of a healthy food chain. We found small effects on soil enzymes activities and that soil bacteria were more susceptible to herbicide contamination than fungi. However, investigation the food chain perspective, we did not find herbicide- or microbiome-mediated effects on the performance of maize plants (Chapter I). These results revealed that herbicides have a reduced impact on the surrounding environment without affecting maize growth, suggesting that herbicides present overall well-designed chemicals.
Taking arsenic contamination of soil as a second stress of a healthy food chain, we found a shift in soil bacterial microbial community, as a response to arsenic toxicity in soil (Chapter II). We did not detect any changes in leaves, root, and kernel microbiomes, as well as in enzyme activities when the soil was challenged with arsenic. These results illustrated the importance of microbiomes in a One Health concept. Interestingly, we discovered a clear positive impact on plant performance by root-secreted benzoxazinoids that help to cope with arsenic stress: plants exuding benzoxazinoids tolerated better soil arsenic toxicity and growth of benzoxazinoid-deficient mutant plants could be rescued by exogenous applied benzoxazinoids (Chapter III).
Hence, we confirmed the multifunctional and beneficial nature of benzoxazinoids, root exudates of grasses, to enhance plant resilience against arsenic in contaminated soils. This finding has a great agronomic potential in crop rotation systems, as it presents a tool to alleviate toxic effects due to soil arsenic contamination and therefore, ensuring better yield of crops in contaminated sites. Taken together the results of this thesis showed the importance of tackling the impact of chemicals introduced or present in the environment that potentially cause health problems to food chains.