Canopy Position Has a Stronger Effect than Tree Species Identity on Phyllosphere Bacterial Diversity in a Floodplain Hardwood Forest

Martina Herrmann,Ronny Richter,Kirsten Küsel,Patricia Geesink

doi:10.1007/s00248-020-01565-y

Abstract

The phyllosphere is a challenging microbial habitat in which microorganisms can flourish on organic carbon released by plant leaves but are also exposed to harsh environmental conditions. Here, we assessed the relative importance of canopy position—top, mid, and bottom at a height between 31 and 20 m—and tree species identity for shaping the phyllosphere microbiome in a floodplain hardwood forest. Leaf material was sampled from three tree species—maple (Acer pseudoplatanus L.), oak (Quercus robur L.), and linden (Tilia cordata MILL.)—at the Leipzig canopy crane facility (Germany). Estimated bacterial species richness (Chao1) and bacterial abundances approximated by quantitative PCR of 16S rRNA genes exhibited clear vertical trends with a strong increase from the top to the mid and bottom position of the canopy. Thirty operational taxonomic units (OTUs) formed the core microbiome, which accounted for 77% of all sequence reads. These core OTUs showed contrasting trends in their vertical distribution within the canopy, pointing to different ecological preferences and tolerance to presumably more extreme conditions at the top position of the canopy. Co-occurrence analysis revealed distinct tree species-specific OTU networks, and 55–57% of the OTUs were unique to each tree species. Overall, the phyllosphere microbiome harbored surprisingly high fractions of Actinobacteria of up to 66%. Our results clearly demonstrate strong effects of the position in the canopy on phyllosphere bacterial communities in a floodplain hardwood forest and—in contrast to other temperate or tropical forests—a strong predominance of Actinobacteria.

Highlights

IntroductionIn forest canopies, they may play a central role in the bioremediation of air pollutants [8] and are in exchange with atmospheric and cloud microbiota, suggesting important implications for climate regulation [7]
Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.The phyllosphere is an important microbial habitat which spans about 108 km2 on a global scale [1]
Leaf samples were obtained from three tree species—Q. robur L., A. pseudoplatanus L., and T. cordata MILL.—in the Leipzig floodplain hardwood forest, located near the city of Leipzig in Germany (Supplementary Fig. 1a)

Summary

Introduction

In forest canopies, they may play a central role in the bioremediation of air pollutants [8] and are in exchange with atmospheric and cloud microbiota, suggesting important implications for climate regulation [7]. Beyond their role in biogeochemical processes, phyllosphere microbiota are passive inhabitants on surfaces of plants but interact with their host in multiple ways [9], resulting in plantmicrobe relationships that range from loose associations to defined symbioses [7]. They produce phytohormones or affect the production of these hormones by the plant [10,11,12] and they improve host resistance against pathogens [13, 14]

Methods

Results

Discussion

Conclusion