Facilitation from an intraspecific perspective – stress tolerance determines facilitative effect and response in plants

Abstract

Summary Plant–plant interactions are reciprocal and include effects on and response to neighbours. Distinct traits confer competitive effect and response ability, but how specific traits determine effect and response in facilitative interactions has not been studied experimentally. We utilized the model species Arabidopsis thaliana to test for trait dependence of facilitative interactions. Salt‐sensitive (sos) mutants or salt‐tolerant wild‐types were exposed to an experimental salinity gradient with and without intraspecific neighbours and the intensity of plant–plant interactions was measured for three performance variables. We tested whether salt tolerance can predict facilitative effect and response and whether a tradeoff exists between competitive ability and tolerance to stress. Interactions shifted very clearly from negative to positive with increasing stress. Salt‐sensitive genotypes were less negatively affected by competition but more dependent on facilitation than were wild‐types, indicating a tradeoff between competitive ability and stress tolerance. Surprisingly, sensitive genotypes imposed stronger facilitative effects, despite being much smaller under stress, probably because they retrieved more salt from the soil. Stress tolerance defined facilitative effect and response via distinct mechanisms. We advocate more controlled experiments with model species to advance our understanding of the trait dependence of biotic interactions and their consequences for community organization.

Density-dependence tips the change of plant–plant interactions under environmental stress

“…However, few existing studies have attempted to explicitly link density-dependence with changes of plant interactions along stress gradients. Facilitation involves benefactors and beneficiaries, i.e., stress amelioration by benefactors (facilitative effect) and sensitivity of beneficiaries to this amelioration (facilitative response) are equally important 34 . Nevertheless, most studies focus either on beneficiaries or on benefactors alone 35,36 and so are the few studies investigating density-dependence 24,27 .…”

“…Indeed, facilitation may be observed less easily among conspecifics due to larger niche overlap 19,20 and stronger intraspecific competition. However, the advantage is that it could provide a general framework, which is unconfounded by species-specifity of facilitative effect and response 34,39 . Namely, (conspecific) benefactors and beneficiaries do not differ in their niches and are affected similarly by any given stress factor and vice-versa, share the very same resources.…”

“…To that end, we conduct a parallel greenhouse experiment with the model plant Arabidopsis thaliana which are grown in a fullfactorial setting along both a density and a salinity gradient. Salinity is selected as the stress factor, because it is easy to manipulate quantitatively 34 and has been well studied 29,34,43 .…”

Can competitive asymmetries maintain offspring size variation? A manipulative field test

“…We provide some support for these modelssmaller offspring were advantageous when stress was reduced (albeit through facilitation, rather than fecundity), whereas larger offspring won when stress was not ameliorated (i.e., neighborfree conditions). Surprisingly, stress-tolerance models do not consider that facilitation may create spatial heterogeneity in stress for propagules (D'Andrea et al 2013;Muller-Landau 2010), despite well-established links between facilitation and stress tolerance more generally (Liancourt et al 2005;Zhang and Tielbörger 2019). Given our findings, explicit exploration of positive interactions may greatly extend these theories.…”

“…; Muller‐Landau ), despite well‐established links between facilitation and stress tolerance more generally (Liancourt et al. ; Zhang and Tielbörger ). Given our findings, explicit exploration of positive interactions may greatly extend these theories.…”