Abstract
The outcome of plant interactions is strongly dependent on the set of
physiological, morphological, and reproductive traits harboured by the
interacting species. Two trait-based mechanisms are behind these plant
interactions: a) trait dissimilarities, when species with similar traits
compete more due to niche overlap, and b) trait hierarchies, when
species with more efficient traits outcompete species with inefficient
traits. Trait dissimilarities present a negative relationship between
plant functional distance and interaction strength, and a positive
relationship for trait hierarchies. We hypothesised that functional
distance between species affect the outcome of plant interactions
through both mechanisms. We established a manipulative experiment with
ten species growing in hetero- and conspecific pairwise combinations and
evaluated thirteen above- and belowground traits. We estimated neighbour
effect by measuring the relative change (RC) in trait values of a focal
species (RCfocal) caused by the presence of a heterospecific neighbour
(RCneighbour), contrasted with the changes induced by a conspecific
neighbour. We explored i) which traits were more affected by neighbours,
ii) which species were more affected as focal or neighbour, and iii) how
the neighbour effect varied with the functional distance between pairs.
Neighbour effects on focal traits showed a variable intensity,
contingent upon the specific identities of both plant species within the
pair. Despite the high variability in neighbour effects, species that
grew with a functionally similar neighbour exhibited larger traits than
those growing with a dissimilar one due to the prevalence of trait
hierarchies over trait dissimilarities. The heterogeneity found on the
neighbour effects responded mainly to differences between above- and
belowground traits, reinforcing the need to consider them both for a
mechanistic comprehension of community dynamics. Trait hierarchies
prevailed but trait dissimilarities were also detected on specific root
traits, indicating that both mechanisms simultaneously determine the
outcome of plant interactions.