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.