Fungicides affect the structure and function of soil microorganisms and the physiology of four riparian tree species, evidence from a pot experiment

Fungicides are a central part of the global plant protection strategy. Unintended side effects of fungicides are changes in soil microbial diversity and activity. However, their direct and indirect effects on plant health, particularly within riparian ecosystems, are hardly assessed. Here, we assessed changes in soil bacterial and fungal community structure and their carbon processing in terms of CO2 and CH4 emission under increasing fungicide concentrations crossed with four tree species, namely field maple (Acer campestre L.), rowan (Sorbus aucuparia L.), common oak (Quercus robur L.) and horse chestnut (Aesculus hippocastanum L). RNA metabarcoding data uncovered that the alpha diversity of fungal communities was more strongly affected by increasing fungicide concentrations relative to bacteria. The impact on fungal community structure was not only a function of fungicide concentration but also dependent on the tree species, a pattern reflected by carbon emissions. At the same time, fungicides directly affected tree height and perimeter negatively of all four tree species. Moreover, indirect effects on plant growth through changes in the soil microbial community are possible. As riparian zones in agricultural landscapes are not only regularly exposed to fungicides and other agrochemicals but also inhabited by riparian tree species such as those assessed in the present study, cascading effects on ecosystem functions such as organic matter decomposition and secondary production of consumers warrant further attention.