Under pressure: elucidating soil compaction and its effect on soil functions

Modern agricultural practices have exacerbated soil compaction, largely due to the intensification of operations involving heavier machinery and tillage practices. Soil compaction increases soil bulk density and reduces porosity, limiting water and nutrient diffusion within the soil matrix. Soil compaction also alters bacterial and fungal communities in agroecosystems by favouring, for example, anaerobic prokaryotes and saprotrophic fungi. Under these conditions crop yields are reduced, affecting food security. We review recent advances in understanding the impact of compaction on soil physical and chemical characteristics and plant physiological response to this stress, with special emphasis on the effect of soil compaction on bacterial and fungal communities and their interaction with the plant. Additionally, we discuss recent findings on plant responses to compacted soils that affect the recruitment of root microbiota and how the microbiota could help the plant cope with this stress. We also discuss possible strategies to mitigate the consequences of soil compaction in agricultural settings. Research in soil compaction is far from conclusive about the mechanisms that plants use to respond to compaction. It is also not well understood how the microbiota inhabiting the roots participate in the plant response mechanisms to this stress. A better understanding of the mechanisms that drive the selection and establishment of the plant microbial community at the root-soil interface in compacted soils could help find new strategies that, together with existing ones, could improve crop production in compacted soils.