Plant root exudation is a crucial means through which plants communicate with soil
microbes and influence rhizosphere processes. Exudation can also underlie ecosystem
response to changing environmental conditions. Different plant species vary in their root
exudate quantity and quality, but our understanding of the plant characteristics that drive
these differences is fragmentary. We hypothesised that root exudates would be under
phylogenetic control and fit within an exploitative root nutrient uptake strategy, specifically
that high rates of root exudation would link to root traits indicative of exploitative growth.
We collected root exudates from plants grown in field soil, as well as leachates of the
entire plant-soil system, to assess both the quantity and quality of root exudates, and their
interaction with the soil metabolome, across 18 common grassland species.
We found that exudation varied with plant functional group and that differences were trait
dependent. Particularly, root diameter, root tissue density and root nitrogen content
explained much of the variation in exudate metabolome, along with plant phylogeny.
Specific root exudation rate was highest in forbs and was negatively correlated with root
tissue density, a trait indicative of conservative resource use strategy, and positively
correlated to root diameter, which is associated with microbial collaboration and resource
Synthesis: We provide novel insight into species-specific differences in root exudates and
identify root functional traits that might underlie these differences. Our results show that
root exudation fits, although not entirely, within current models of the root economic
space, with strong positive relationships to outsourcing traits like high root diameter.
Determining the role of root exudates as a key facet of the resource outsourcing strategy
necessitates further research into the fundamental controls on root exudation quantity and
quality, particularly during environmental change.