Trait variation and plant performance: Interactive effects of diversity and spatial patterning of plants across environmental conditions

The diversity and spatial patterning of plants and their environmental determinants can influence plant–plant interactions critical to generating trait variation in plants. However, how plant spatial patterns interact with plant diversity to shape intra- and interspecific trait variation and, in turn, shape plant performance remains unclear. It is also unclear how the availability of resources influences these relationships. We created experimental assemblages varying in the spatial distributions of the diversity of plant species under ambient watering and induced drought conditions and collected data on leaf traits and plant performance (cf. whole plant biomass). Our analyses revealed that multitrait intra- or interspecific variation (quantified as the coefficient of variation and averaged across species and traits) was positively associated with plant diversity regardless of environmental conditions. However, the magnitudes of multitrait intraspecific variation were slightly lower for spatially structured than randomly distributed plants under ambient conditions. While multitrait interspecific variation did not vary among environmental conditions, multitrait intraspecific variation was 13.64% higher under drought than in ambient conditions. Intra- and interspecific variations in individual traits generally agreed with the trends observed for the multitrait variation, but species-specific intraspecific trait variation was idiosyncratic. Further analyses of this data revealed that plant performance was negatively associated with multitrait interspecific variation across environmental conditions, but plant performance was negatively associated with multitrait intraspecific variation under drought only, suggesting trait variation (quantified as CV) as an indicator of competitive hierarchy in this experiment. For individual traits, however, intra- or interspecific trait variation and plant performance association varied from positive and negative to neutral depending on traits and environmental conditions. Our results highlight the importance of considering the environmental condition-dependent interaction between diversity and spatial patterning of plants for understanding the causes and consequences of trait variation under present or future global change scenarios. Read the free Plain Language Summary for this article on the Journal blog.