Microbial community function increases host plant leaf growth in a pitcher plant experimental system

Abstract

Across diverse ecosystems, bacteria and their host organisms engage in complex relationships having negative, neutral, or positive interactions. However, the specific effects of leaf-associated bacterial community functions on plant growth are poorly understood. To address this gap, we explored the relationships between bacterial community function and host plant growth in the purple pitcher plant (Sarracenia purpurea). The main aim of our research was to investigate how different bacterial community functions affect the growth and nutrient content in the plant. Previous research had suggested that microbial communities may aid in prey decomposition and subsequent nutrient acquisition in carnivorous plants, including S. purpurea. However, the specific functional roles of these bacterial communities in plant growth and nutrient uptake are not well known. In this study, sterile, freshly opened leaves (pitchers) were inoculated with three functionally distinct, pre-assembled bacterial communities and effects examined over 8 weeks. Bacterial community composition and function were measured using physiological assays, metagenomics, and metatranscriptomics. Distinct bacterial functions affected plant traits; a bacterial community enriched in decomposition and secondary metabolite production traits was associated with larger leaves with almost double the biomass of control pitchers. Physiological differences in bacterial communities were supported by metatranscriptomic analysis; for example, the bacterial community with the highest chitinase activity had greater expression of transcripts associated with chitinase enzymes. The relationship between bacterial community function and plant growth observed here indicates potential mechanisms for host-associated bacterial functions to support plant health and growth.