Plant neighbors differentially alter a focal species’ biotic interactions through changes to resource allocation

Plant resource allocation strategies are thought to be largely a
consequence of changing abiotic conditions and evolutionary history.
However, biotic interactions also influence how a plant allocates
resources. As a result, plants mediate indirect interactions between
organisms above- and belowground through resource allocation. Neighboring
plants can influence plant fitness directly through competition for
resources, and indirectly by altering associated community interactions
(associational effects). Given the importance of community interactions
for plant success, and the known ability for plant neighbors to change
these interactions, the goal of this “pandemic project” was to separate
inter- and intraspecific plant associations, above- and belowground, to
understand how different plant neighbors alter plant resource allocation,
and if this in turn alters biotic interactions. We specifically
investigated associational effects on herbivory and soil microbial
community interactions. To do so, we established a common garden
experiment, manipulating plant neighbors and extent of interactions
(aboveground only versus above- and belowground interactions, using
customized pot types), and measured changes to a focal plant and its
biotic interactions over two growing seasons. We found evidence of both
neighbor effects and pot type, showing that neighbor interactions affect a
focal plant through both above- and belowground processes, and how the
focal plant is affected depends on neighbor identity. Though neighbors did
not directly alter herbivory or most soil microbial interactions, they did
alter the relationship between belowground microbial communities and plant
function. Resource allocation responses were reduced with time, showing
the importance of extending experiments beyond a single growing season,
and is an important consideration when making predictions about plant
responses to changing conditions. This study contributes to a growing body
of work showing how the community context affects the above- and
belowground interactions of a plant through plant resource allocation
strategies.