Testing the role of functional trait expression in plant–plant facilitation

Abstract

1. Positive biotic interactions between plant species may strongly affect species and community-level patterns, but the processes through which benefactor species alter the performance of interacting species (via, e.g. beneficial mechanisms like resource provisioning) are still inadequately understood. One poorly explored potential explanation is that plant-plant facilitation could occur through the impact of benefactor species on the functional trait expression of beneficiary species. Indeed, plant species that affect local conditions can modify functional trait expression of interacting species, thereby improving their performance and resulting in a facilitative interaction. However, the response of intraspecific trait variation to biotically driven microhabitat modification, and its role in determining the outcome of plant-plant interactions, has rarely been explored. 2. Here, we test whether growing with benefactor species affects the expression of functional traits of eight species, encompassing different plant growth forms, in two contrasting study systems. This is achieved using a paired sampling approach to compare values of seven functional traits of conspecific individuals growing within and adjacent to cushion plants (i.e. benefactor species which are known to strongly alter microhabitat conditions and to have positive effects on some of the focal species). In addition, we test whether the effect of biotic interactions on functional trait expression changes along elevational gradients, as the outcome of biotic interactions is expected to vary with elevation. 3. Contrary to predictions, in both systems, intraspecific trait variation was not well explained by the biotic interaction with the cushion plant species or the variation in abiotic conditions associated with elevational gradients. Where biotic interactions did affect functional trait expression and bivariate trait relationships, traits responded variably between species, suggesting that context specificity may be a constraint to predicting how intraspecific trait variation responds to plant-plant interactions, adding to the growing body of literature that challenges the generality and predictability of the drivers of intraspecific trait variation. 4. This research, therefore, suggests that benefactor species' facilitative process is likely not through an impact on intraspecific trait expression, and that instead other processes may be more important for translating beneficial microhabitat 256 | Functional Ecology van der MerWe et al.

Precipitation effects on grassland plant performance are lessened by hay harvest

“…These results show that these species are benefited by greater LAI and increased community richness when only precipitation increased; yet are not influenced by biotic variables if hay harvest co-occurs with changes in precipitation. Neighbors around focal plants ameliorate some or many environmental conditions, allowing species to grow despite harsh conditions 20 . Hence, we posit that microhabitat amelioration by neighbors’ presence was key for other species performance ( Ambrosia psilostachya , Croton monanthogynus , Symphyotrichum ericoides, Schizachyrium scoparium, Sorghastrum nutans and Sporobolus compositus ), including species that are known to be less abundant in the community.…”

“…Species in a community might ameliorate the environmental stress for other species by facilitating their coexistence, establishment or growth 17 – 19 . For example, neighboring species ameliorate some or many stressful environmental conditions, causing positive impacts on focal species 20 , and plants of different growth forms can alter the canopy structure of plant communities 21 , resulting in competitive hierarchies with effects on the plant performance due to the directional supply of light 22 – 24 . Plant communities thus exhibit a particular suite of varied species performance as a result of particular combinations of biotic structure 25 , 26 , yet under severe environmental change, biotic structure may become unimportant to determine plant performance, relative to the effect of the abiotic stress.…”

Shoot–Root Interplay Mediates Defoliation-Induced Plant Legacy Effect

“…The linkage of functional traits with plant adaptation and ecological functioning have been addressed in previous studies ( Garnier and Navas, 2012 ; van der Merwe et al, 2021 ). Results from the present study provided a new addition to this trait-based approach from the perspective of trait plasticity under defoliation.…”

“…Plant traits can reflect the general response and trade−offs (or coordination) of the ecological function of environmental fluctuations ( Abalos et al, 2018 ; van der Merwe et al, 2021 ). Thus, a trait-based approach allows a better understanding of how plants respond to external disturbance ( Garnier and Navas, 2012 ).…”

Directly quantifying multiple interacting influences on plant competition

“…Global meta‐analyses (Kunstler et al, 2016) suggest that the presence of any neighbour has the greatest negative effect on growth (an outcome of competition, as we define it), irrespective of particular traits the species in question can express, and that a neighbour of the same species is likely to have a bigger effect than a neighbour of another species. But locally, the interaction between neighbours depends absolutely on how both intra‐ and interspecific individuals respond physiologically and developmentally to their immediate location and to each other, and on the nature of the competed‐for resource, but trait expression is also highly context‐dependent (Van der Merwe, Greve, Olivier, & le Roux, 2020).…”