Data and code from: Is a plant truly plastic? Nutrients and neighbours induce trait-specific responses, but performance depends on response direction

Plants live in a heterogeneous world, where nutrient and neighbour
distributions vary in space and time. Plants can respond to this variation
through plastic responses in individual organs, which are assumed to be
coordinated among traits to support a coherent, adaptive strategy,
maintaining plant growth in varying environments. However, this assumption
remains understudied. Here, we test coordination in trait plasticity and
its influence on plant performance. We do so among 27 naturally
co-occurring species under four different neighbour and soil fertility
contexts using data from two mesocosm experiments manipulating nutrients
and neighbour presence. We focus on commonly-studied resource-acquisitive
traits: specific leaf area (SLA), root tissue density (RTD), and specific
root length (SRL). We found species exhibited plasticity in SLA, RTD, and
SRL 50-75 % of the time and that responses to neighbours were stronger
than nutrients for SLA and RTD, but not SRL. However, plastic responses
were highly modular, correlated < 10 % of the time, and
had little coordination consistent with the trait economics paradigm.
Consequences of plasticity for plant performance depended on the trait,
the response direction, and whether plants were responding to nutrients or
neighbours. Plasticity in RTD was unrelated to performance, but species
that increased their SRL under low nutrient conditions performed worse
than those showing no SRL plasticity, while SRL responses to neighbours
had no effect. Similarly, species that increased SLA under low nutrients
or with neighbours showed reduced performance compared to those that
decreased SLA in those same conditions. Overall, plasticity in SLA, RTD,
and SRL rarely manifested as a correlated or coordinated response
promoting growth maintenance in our study. Instead, plasticity’s
consequences hinged on the direction of trait shifts, sometimes incurring
costs. Future studies should consider plasticity a directional phenomenon.