Intraspecific variation in plant traits mediated by neighborhood composition and its effects on ecosystem properties in a tree functional diversity experiment

Background/Question/Methods

One dominant hypothesis to explain over-yielding (or rates of ecosystem processing or stability) in biodiversity experiments is complementary resource use among species. An extension to this might be that individuals of a species plastically mold their traits such that their resource use is even more (or less) complementary to others in an assemblage. Here we asked whether species traits differ with assemblage composition and whether these differences scale to affect ecosystem properties. We focused on a single resource axis: light. We measured leaf- and plant-level traits and plot-level properties related to light capture for 12 tree species grown in monoculture and mixtures of varying species richness and functional diversity as part of a high-density tree diversity experiment near Montreal, QC, Canada. The experiment is part of the IDENT initiative.

Results/Conclusions

We found that species’ organ-level traits (e.g. specific leaf area) and leaf display (e.g. crown shape) differed with assemblage composition. For instance, the crown shape of some species differed among assemblages, reflecting the crown shape of neighboring trees. The magnitude and direction of trait shifts relative to monoculture depended both on the species and the composition of the assemblage. Differential shifts in the crown size and leaf display of species in mixtures compared with monocultures can account for differences among plots in leaf area index and light interception. These results suggest that the trait variation driven by species interactions within communities can scale up to affect ecosystem properties. These results open the door to examine whether such outcomes of neighborhood interactions follow predictable rules.