The accumulation of species-specific enemies around adults is hypothesized to maintain plant diversity by limiting the recruitment of conspecific seedlings relative to heterospecific seedlings1,2,3,4,5,6. Although previous studies in forested ecosystems have documented patterns consistent with the process of negative feedback7,8,9,10,11,12,13,14,15,16, these studies are unable to address which classes of enemies (for example, pathogens, invertebrates, mammals) exhibit species-specific effects strong enough to generate negative feedback17, and whether negative feedback at the level of the individual tree is sufficient to influence community-wide forest composition. Here we use fully reciprocal shade-house and field experiments to test whether the performance of conspecific tree seedlings (relative to heterospecific seedlings) is reduced when grown in the presence of enemies associated with adult trees. Both experiments provide strong evidence for negative plant–soil feedback mediated by soil biota. In contrast, above-ground enemies (mammals, foliar herbivores and foliar pathogens) contributed little to negative feedback observed in the field. In both experiments, we found that tree species that showed stronger negative feedback were less common as adults in the forest community, indicating that susceptibility to soil biota may determine species relative abundance in these tropical forests. Finally, our simulation models confirm that the strength of local negative feedback that we measured is sufficient to produce the observed community-wide patterns in tree-species relative abundance. Our findings indicate that plant–soil feedback is an important mechanism that can maintain species diversity and explain patterns of tree-species relative abundance in tropical forests.
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We thank G. Adler, M. Kaspari, E. Leigh, T. Lambert, I. Rubinoff, E. Tanner, M. Tobin, B. Turner, S. Van Bael and N. Wurzburger for providing discussions and comments on the manuscript. R. Kolodziej, K. Meyer, K. McElligott and T. Shirshac provided greenhouse and field assistance. Logistical support was provided by the Smithsonian Tropical Research Institute. The Center of Tropical Forest Science provided BCI tree abundance data published online at https://ctfs.arnarb.harvard.edu/webatlas/datasets/bci/abundance. This study was supported by a Smithsonian Tropical Research Institute (STRI) postdoctoral fellowship to S.A.M., a University of Wisconsin–Milwaukee (UWM) Research Growth Initiative grant to S.A.S., a fellowship from the UWM Research Foundation, and a grant from the National Science Foundation to J.D.B. We thank I. Rubinoff for his support of the STRI Soil Initiative.
This file contains Supplementary Tables 1-3, Supplementary Figures 1-2 with legends, a Supplementary Discussion, and Supplementary Equations.