By influencing soil biota and nutrient cycling, plants can alter their
fitness and that of their neighbours through plant-soil feedbacks.
However, we need more detailed understanding of the biological causes of
such feedbacks. This includes identifying the soil microbial guilds
causing them. As most plant-soil feedbacks have been reported to be
negative, the dominant paradigm is focused on the accumulation of soil
pathogens. This neglects the full range of soil microorganisms likely to
influence plant performance. Here, we studied plant growth responses to
field-collected soil inocula in a large-scale greenhouse study coupled
with next-generation sequencing. Although we found a high prevalence of
negative plant-soil feedbacks, the microorganisms driving the responses
were largely saprotrophs and N-cycling prokaryotes, not pathogens. These
results show that negative plant-soil feedbacks need not be caused by
trophic interactions, highlighting the need to bring back nutrient
cycling as a central component of plant-soil feedbacks.