Julia Jimeno-Alda

and 3 more

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.