The Ecology and Natural History of Foliar Bacteria with a Focus on Tropical Forests and Agroecosystems

Abstract

Leaves of higher plants comprise perhaps the largest bacterial substrate on earth, yet we know very little about the bacteria that occupy these spaces. In this review, we first examine the ecology and behavior of bacteria that reside on leaf surfaces. Next, we discuss the ecological implications of foliar bacteria that reside in interior portions of leaf tissues. Later, we consider the studies on foliar bacteria in tropical habitats to date. Finally, we examine evidence regarding the potential roles of foliar bacteria in structuring tropical plant communities. Bacteria colonize the phyllosphere via animal vectors or passively from soil, wind, or rain, though there are too few data to determine the relative contributions of these sources to the phyllosphere. Additionally, the degree to which parent plants transmit bacteria to offspring via seed remains unknown. We predict that high temperature, high humidity, low UV radiation, and leaf architecture in the tropical understory enable tropical leaves to support more abundant and diverse bacterial communities compared to temperate leaves. While the extent of competitive interactions among bacteria remains poorly resolved, evidence from agricultural crop species and Arabidopsis thaliana suggests that these interactions cause niche partitioning based on carbon use. The degree to which phyllobacteria and endophytes of tropical plants are pathogenic versus mutualistic or neutral remains unexplored. We hypothesize, however, that the detrimental impact of bacterial pathogens ultimately increases as the abundance of single host tree species increases, which can promote and maintain plant diversity in tropical forests.