Patterns and consequences of plant trait variation: roles of plant spatial patterns, diversity, and drought

The diversity and spatial patterns of plants and environmental severity 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 and whether the conclusion varies between productive and severe environments remain unclear. To address this gap, we manipulated plant spatial patterns and diversity in an old field simultaneously under ambient watering and drought conditions. We collected data on leaf traits related to resource acquisition (leaf area, specific leaf area and leaf chlorophyll content) and those related to the conversion of acquired resources to masses (leaf dry matter content and leaf thickness) paired with plant performance (cf. plant biomass). We found a positive association between multitrait intra- or interspecific variation and plant diversity across ambient watering and drought conditions and a slightly lower degree of multitrait intraspecific variation for spatially structured (i.e., positively or negatively autocorrelated) plants than randomly occurring plants under ambient watering. Although multitrait interspecific variation did not vary between ambient watering and drought conditions, the multitrait intraspecific variation was significantly higher under drought than ambient watering conditions. Intriguingly, interspecific variation in resource acquisition-related traits (important for niche difference) was positively associated with plant performance across ambient watering and drought conditions, while intra- and interspecific variations in resource conversion-related traits (important for plant growth and persistence) were negatively associated with plant performance. However, when all traits were lumped, intra- or interspecific variation was negatively associated with plant performance, signaling a competitive hierarchy. Patterns and mechanistic interpretation of the trait variation-plant performance association may thus depend on trait choice and environmental contexts. Overall, this study presents one of the first experimental demonstrations of the joint effects of plant spatial patterns and diversity on plant trait variation and its consequences for plant performance in contrasting environments. Although the patterns and consequences of intra- and interspecific trait variations seem context-dependent (i.e., individual traits and environment-dependent), looking into trait variation through resource acquisition versus resource conversion axes can offer useful insights valuable for the progress of trait ecology.