Colonization timing plays an important role in community assembly. Priority effects provide early arriving species with an advantage, giving them first access to limited resources and space, negatively impacting later arriving species. Exotic plant species are less negatively impacted by interspecific priority effects, but intraspecific effects are unknown. Our study aims to understand how priority effects impact ‘early’ vs. ‘late’ arriving plant genotypes during population assembly to generate intraspecific variation and diversity. Increasing intraspecific diversity promotes ecosystem function similarly to increasing interspecific diversity. Therefore, our study also addresses how variation in mesocosm performance affects ecosystem function (NEE). We collected four grass species (native: Sorghastrum nutans, Schizachyrium scoparium; exotic: Sorghum halepense, Bothriochloa ischaemum) from across the precipitation gradient of Oklahoma, using four genotypes per species based on phenotypic similarity (low to high). Each mesocosm had one, two (‘early’ arrival treatments) or three individuals (control) and after 21 days one or two individuals (‘late’ arrival treatment) were added for three total individuals per pot. We measured mesocosm NEE and harvested above- and belowground biomass for each individual in each mesocosm. We calculated standardized effect sizes to determine the impact of “early” vs. “late” arrival on plant genotype performance for each species.
Results/Conclusions
Early arriving genotypes, for both native and exotic plant species, were either negatively positively or not impacted relative to the control treatments. S. scoparium genotypes, one of our native populations, was negatively impacted by early arriving suggesting facilitation occurs when genotypes are grown together. On the other hand, S. halepense genotypes benefited from early arrival due perhaps to antagonistic interactions among exotic genotypes. Late arrival into mesocosms negatively impacted all genotypes, native and exotic, relative to control mesocosms. Surprisingly, phenotypic neighbor similarity did not explain plant genotype performance. In other words, arriving in mesocoms with similar or dissimilar neighbors produced similar outcomes. Generally invasive mesocosms had greater total biomass production and NEE than native mesocosms. Taken together, our results indicate that priority effects act to reduce plant genotype performance during late arrival across both native and exotic plant populations with mixed results in terms of benefits of early arrival.