Microbial nitrification in throughfall of a Japanese cedar associated with archaea from the tree canopy.

Keiji Watanabe,Takejiro Takamatsu,Masami Kanao Koshikawa,Akio Takenaka,Seiji Hayashi,Ayato Kohzu,Mirai Watanabe,Wataru Suda,Shigeki Yamamura

doi:10.1186/s40064-016-3286-y

Abstract

To investigate the nitrification potential of phyllospheric microbes, we incubated throughfall samples collected under the canopies of Japanese cedar (Cryptomeria japonica) and analyzed the transformation of inorganic nitrogen in the samples. Nitrate concentration increased in the unfiltered throughfall after 4 weeks of incubation, but remained nearly constant in the filtered samples (pore size: 0.2 and 0.4 µm). In the unfiltered samples, δ18O and δ15N values of nitrate decreased during incubation. In addition, archaeal ammonia monooxygenase subunit A (amoA) genes, which participate in the oxidation of ammonia, were found in the throughfall samples, although betaproteobacterial amoA genes were not detected. The amoA genes recovered from the leaf surface of C. japonica were also from archaea. Conversely, nitrate production, decreased isotope ratios of nitrate, and the presence of amoA genes was not observed in rainfall samples collected from an open area. Thus, the microbial nitrification that occurred in the incubated throughfall is likely due to ammonia-oxidizing archaea that were washed off the tree canopy by precipitation.

Highlights

The phyllosphere is a hostile environment for microbes because the leaf surface is deficient in nutrients and exposed to dry conditions and strong UV radiation (Yang et al 2001)
For throughfall from Cj1 (Fig. 2), nitrate concentrations in the unfiltered sample increased during 4 weeks of incubation, whereas there was almost no nitrate production in samples passed through the 0.2, 0.4, and 2-μm-pore filters
Ammonium decreased in all samples during 4 weeks of incubation, the decreases were larger in the unfiltered samples and those that passed through 2- and 10-μm-pore filters

Summary

Introduction

The phyllosphere is a hostile environment for microbes because the leaf surface is deficient in nutrients and exposed to dry conditions and strong UV radiation (Yang et al 2001). Bacteria exist in the phyllosphere at an estimated average density of 106–107 cells cm−2 (Lindow and Brandl 2003). If phyllospheric microbes metabolize nutritional elements (e.g., N and S), they may play an important role in the biogeochemical cycles of these elements. Phyllospheric microbes have been well studied and include plant pathogens and their antagonists, ice-nucleation bacteria, decomposers, phytohormone producers, and nitrogen fixers (Fett et al 1987; Hirano and Upper 2000; Enya et al 2007; Fürnkranz et al 2008; Suda et al 2009; Vorholt 2012). There is limited information available regarding the contribution of phyllospheric microbes to elemental dynamics (e.g., Woods et al 2012)

Methods

Results

Discussion

Conclusion