Feedbacks in a mixed mycorrhizal rainforest in Sri Lanka are more stabilizing in the field than in the shadehouse

Background and Aims: Long-lived adult trees influence local biotic and abiotic properties that in turn influence tree seedlings. Such feedbacks are important stabilizing processes that maintain local-scale diversity. However, the role of these feedbacks in determining coexistence outcomes – measured as pairwise feedback – is poorly understood for long-lived trees, particularly in the tropics. We address this knowledge gap through pairwise experiments in the shadehouse and in the field within a mixed-mycorrhizal tropical forest of Sri Lanka. We predicted that pairwise feedbacks would be negative, and therefore stabilizing, because the selected tree species coexist in nature. Methods: In the shadehouse, we planted 402 seedlings of five species into soils conditioned by adult trees of each species. In the field, we planted 320 seedlings of four species beneath adult trees of each species. After ~1.3 years, we calculated survival-adjusted, final above-ground biomass to compute pairwise feedback values for all species pairs. Results: Based on vote counting, mean pairwise feedbacks were positive for 8 of 10 pairs in the shadehouse and negative in 4 of 6 pairs in the field experiment. Pairwise feedbacks were more negative in the field than in the shadehouse, suggesting feedbacks are due to above-ground enemies rather than soil-borne pathogens. These negative pairwise plant-neighbourhood feedbacks in the field appear to be due to contributions to stabilization among heteromycorrhizal but not conmycorrhizal pairs. Conclusion: Some stabilization among heteromycorrhizal pairs in the field may contribute to coexistence in Asia’s mixed mycorrhizal forests. Our study also demonstrates the importance of using in situ experimental approaches to assess the role of negative feedback in plant species coexistence in nature. These data help reproduce figures and tables in the article titled, "Feedbacks in a mixed mycorrhizal rainforest in Sri Lanka are more stabilizing in the field than in the shadehouse" in Plant and Soil