Root responses to neighbors depend on neighbor identity and resource distribution

In a complex soil environment, competitive and environmental factors will
interact with individual traits to influence a plant’s root growth
patterns and ability to compete for resources. Here, we examine how root
growth of a focal plant, Plantago lanceolata L., responds to resource
heterogeneity and to presence of two neighbor species, Centaurea jacea
L.and Poa pratensis L. A full factorial experiment tested the effects of
nutrient heterogeneity, neighbors, and their interaction on root responses
of Plantago. Roots in shared quadrants of a pot were harvested and
quantified by qPCR for plants grown alone or with a neighbor, in patchy or
even soil. The effects of experimental treatments on Plantago root mass
distribution were tested with two-way ANOVA. When soil resources were
evenly distributed, Plantago individuals increased root allocation to soil
shared with a Centaurea neighbor but not a Poa neighbor. When soil
resources were patchy, Plantago responded more strongly to Poa than to
Centuarea, and placed more roots in the high-resource patch. These results
demonstrate that plants can respond differently to neighbors depending on
species and that integrating multiple cues results in non-additive effects
on root behavior.