Data from: Corrections for rooting volume and plant size reveal negative effects of neighbour presence on root allocation in pea

Plants are able to detect the presence of their neighbours belowground.
The associated root responses may affect plant performance, plant-plant
interactions and community dynamics, but the extent and direction of these
responses is heavily debated. Some studies suggest that plants will
over-proliferate roots in response to neighbours at the expense of
reproduction, which was framed as a “tragedy of the commons”. Others
proposed an “ideal free distribution” hypothesis, stating that plants
produce roots simply as a function of the amount of available nutrients.
However, experimental evidence for either hypothesis that is unbiased by
confounding effects of rooting volume and plant size in their experimental
setups is still lacking. We grew split-root pea plants in the presence or
absence of a belowground neighbour at a range of rooting volumes, while
providing equal amounts of nutrients per plant. Path analyses were used to
disentangle the direct effects of neighbour presence on allocation
patterns from the confounding effects of rooting volume and plant size.
Within the chosen range of rooting volumes, the presence of a belowground
neighbour generally reduced plant root mass by 21% and total mass by 9%. A
doubling of rooting volume generally increased plant root mass by 18% and
total mass by 11%. Pod mass was only directly and positively correlated
with vegetative mass. The presence of a belowground neighbour induced less
root allocation but more pod allocation, whereas increased rooting volume
caused a reduction in reproductive allocation. A large part of these
effects, however, was indirectly mediated through the influence on plant
total mass. Synthesis: Not considering the effects of rooting volume and
plant size may lead to misinterpretations of plant growth strategies in
response to neighbours. Accounting for these factors, we found pea
allocating less mass to roots in the presence of a belowground neighbour.
The obtained results can help to reconcile the various responses to
belowground neighbours as they are published in the literature.