COS 76-3
Do foliar bacteria impact metrics of seedling performance along a nutrient supply gradient: Results from a long-term experiment in a tropical forest in Panama
Enemies of plants enhance plant diversity by altering competitive interactions among species. Foliar bacteria in particular may facilitate plant diversity maintenance if they vary in their impact on host species, however this remains unknown. We examined the degree to which foliar bacteria impacted seedlings in the understory of a tropical forest along replicated resource supply treatments. We specifically focused on seedlings because the interactions in the understory contribute substantially to the eventual canopy composition. Furthermore, seedlings may be particularly vulnerable to bacterial pathogens or conversely require these bacteria as mutualists. We tested the following hypotheses: 1. Foliar bacteria will cause a major reduction in plant performance in situ 2. Impact of foliar bacteria will be greatest when soil resources are low. To test these hypotheses, we used five host tree species (Alseis blackiana, Desmopsis panamensis, Heisteria concinna, Sorocea affinis, and Tetragastris panamensis) in the shaded understory of a lowland tropical forest in Panama. We used a 16-year nutrient enrichment experiment on the Barro Colorado Nature Monument where nitrogen, potassium, and phosphorus were added to large plots (40 x 40 m) in a fully factorial design (n=4). We applied commercial antibiotics to replicated individuals with paired untreated controls in the experimental plots.
Results/Conclusions
To address these hypotheses, we quantified growth, survivorship, leaf production and longevity, and herbivore and disease damage for over 900 seedlings across the plots for 29 months. Our results indicate that foliar bacteria significantly decreased plant performance in the field. The degree to which bacteria impacted performance as well as leaf longevity and herbivore and pathogen damage differed among tree species. Furthermore, soil fertilization mitigated their impact on plant hosts. Additionally, our results demonstrate that the negative effects of foliar bacteria are exacerbated in low nutrient habitats. These findings suggest there are potential implications for the maintenance of tree diversity in tropical forests. Specifically, foliar bacteria may promote plant diversity by decreasing the regeneration of dominant trees or reduce diversity by causing higher mortality of rarer species.